Darwin on animal tool use
Next time you hear that everybody knew that humans were the only toolmaker before Jane Goodall showed otherwise:
It has often been said that no animal uses any tool; but the chimpanzee in a state of nature cracks a native fruit, somewhat like a walnut, with a stone.23 Rengger24 easily taught an American monkey thus to break open hard palm-nuts, and afterwards of its own accord it used stones to open other kinds of nuts, as well as boxes. It thus also removed the soft rind of fruit that had a disagreeable flavour. Another monkey was taught to open the lid of a large box with a stick, and afterwards it used the stick as a lever to move heavy bodies; and I have myself seen a young orang put a stick into a crevice, slip his hand to the other end, and use it in the proper manner as a lever. In the cases just mentioned stones and sticks were employed as implements; but they are likewise used as weapons. Brehm25 states, on the authority of the well-known traveller Schimper, that in Abyssinia when the baboons belonging to one species (C. gelada) descend in troops from the mountains to plunder the fields, they sometimes encounter troops of another species (C. hamadryas), and then a fight ensues. The Geladas roll down great stones, which the Hamadryas try to avoid, and then both species, making a great uproar, rush furiously against each other. Brehm, when accompanying the Duke of Coburg-Gotha, aided in an attack with fire-arms on a troop of baboons in the pass of Mensa in Abyssinia. The baboons in return rolled so many stones down the mountain, some as large as a man's head, that the attackers had to beat a hasty retreat; and the pass was actually for a time closed against the caravan. It deserves notice that these baboons thus acted in concert. Mr. Wallace26 on three occasions saw female orangs, accompanied by their young, "breaking off branches and the great spiny fruit of the Durian tree, with every appearance of rage; causing such a shower of missiles as effectually kept us from approaching too near the tree."
That's Darwin (1871:51-52), in The Descent of Man. The footnotes are below.
For Darwin, it was important to establish that some non-human primates were capable of complicated behaviors and learning. Tool use and manipulation in other animals provided the possibility of evolutionary intermediates between apes and humans. In characteristic fashion, Darwin is able to bring in a range of observations from different species, some of them obscure (see notes).
The baboon stoning story seemed extreme to me, compared to what I had read about baboons, but Hamilton, Buskirk and Buskirk (1975) describe a very similar scenario:
Anecdotal reports of stone throwing by baboons have been dismissed on the basis of the unreliability of correspondents and the improbability of oriented throwing by a quadruped anatomically incapable of overhand throwing. In spite of several years of field study elsewhere in Africa, often in rocky terrain, there are no reports by professional field observers of deliberate stone throwing by baboons.
Nevertheless, in the course of a one-year study of three chacma baboon (Papio ursinus) troops living on the desert floor of the Kuiseb Canyon in South West Africa we observed numerous instances of stone release directed toward us.
Stoning by these baboons is done from the rocky walls of the canyon where they sleep and retreat when they are threatened by real or imagined predators. STones are lifted with one hand and dropped over the side. The stone tubles down the side of the cliff or falls directly to the canyon floor. We recorded the details of 23 such incidents involving the voluntary release of 124 stones towards us.
...
This frequently resulted in stones whizzing over our heads. usually we could dodge; but occasionally two or more individuals release stones at approximately the same time, complicating evasion. (Hamilton et al. 1975:488).
That doesn't sound quite as intense as the episode Darwin described, but definitely in the same neighborhood. A few words about Brehm's trip to Abyssinia can be found in his Wikipedia entry; the duke in question was Ernst II, Queen Victoria's brother-in-law.
I figure having rocks thrown at you by a baboon definitely beats bombardment by durian fruit.
Darwin's footnotes:
23 Savage and Wyman in 'Boston Journal of Nat. Hist.' vol. iv. 1843-44, p. 383.
24 'Säugethiere von Paraguay,' 1830, s. 51-56.
25 'Thierleben,' B. i. s. 79, 82.
26 'The Malay Archipelago,' vol. i. 1869, p. 87.
References:
Darwin C. 1871. The descent of man and selection in relation to sex. John Murray, London.
Hamilton WJ, Buskirk RE, Buskirk WH. 1975. Defensive stoning by baboons. Nature 256:488-489. doi:10.1038/256488a0
Fatness and scarcity revisited
Via Dienekes: Ember and colleagues (2005) address the question of whether cultural preferences for fatness or thinness in women are related to the prevalance of resource scarcity in a society. The hypothesis that these should be related comes from the work of Brown and Konner (1987). From the current paper:
In most cultures, the ideal female form is not thin. According to Brown and Konner (1987), 81% of societies in a Human Relations Area Files (HRAF) sample preferred plump or moderately fat women, and 90% preferred large or fat hips and legs. (Few anthropological reports discuss preferred male body types.) Brown and Konner suggest that plumpness is generally adaptive because fat stores allowpeople to survive periods of scarcity, as well as being associated with earlier menarche, successful pregnancies, and adequate lactation. But if this be so, why is thinness valued in some cultures (even some preindustrial ones)? At the least, one might expect that these will be cultures with little resource scarcity, and a study by Anderson, Crawford, Nadeau, and Lindberg (1992) supported this hypothesis. However, the research reported here does not (Ember et al. 2005:258).
In other words, the hypothesis is that people should recognize that fatness is adaptive to resource scarcity and should shape their cultural preferences accordingly. A fairly glaring weakness in the hypothesis is its failure to explain a preferences for thinness in many societies, which has no simple economic explanation.
The study finds a relatively strong negative correlation (on the order of -0.5) between valuation of fatness and three measures of scarcity. This contradicts the hypothesis that these should be positively related.
Ember et al. (2005:261-262) discuss the influence of food storage potential on these relationships:
Food storage is not significantly related either to the valuation of fatness in women or to any of our three measures of resource scarcity, but it does modulate their relationships to one another. In societies with little or no storage (score 1), high threat of disasters significantly predicts low valuation of fatness (in our combined samples, q= .56, P=.02, two tails, N=17), as we found in Sample 1, but in societies with some storage (scores 2Ð3), threat of disasters has no relationship to the valuation of fatness in women.
From their negative finding, Ember and colleagues (2005) consider several alternatives, ranging from the idea that thinness may help in some way, to the idea that groups may be selected on the basis of their total energy consumption, to the idea that male preferences are driven by their desire to dominate or control their mates. All of these are found wanting, although the most time is spent on the last.
This is a case where it is unclear how much a correlation can tell you. A relatively strong correlation of around 0.5 or so still explains only a quarter of the variance. In this case, the predicted variable is cultural preference, which means that even a significant correlation with scarcity still leaves many other factors to account for the preference.
And in this case, the "preference" consists of a score based on a few ethnographic interviews. How do individuals within a society vary in their preferences? How extensive is the overlap among societies in the range of variation? To test evolutionary strategies, this is the level of detail that is really necessary, but the available data simply aren't there. So there may be no point to considering the matter further, beyond saying that the "value" that societies place on fat women does not appear to reflect the pragmatic concerns of surviving resource scarcity or famine.
I would suggest an additional hypothesis, one that also focuses on the evolutionary importance of fatness, but in a different way. Fat women (and men) tend to have fat sons (and daughters). In a highly mobile society where running, hunting, competition with other people, or other traits are highly important to survival (and thereby highly valued), men will prefer mates that can give them healthy, fit, and competitive sons. This hypothesis has little to do with people's ability to predict who will survive a famine (which fatness may help a little with, but is not determinative) and much to do with their ability to understand simple heritability.
It is especially applicable to societies who keep domesticated animals, since these people not only have to survive shortfalls themselves, but also have to get their stock through them. And furthermore, fat stock are better tasting and better energy sources (both for meat and milk). If people can breed their animals with eye toward increasing their fatness, they can surely figure out that a fat wife will have similar famine-resisting properties. Thus, a cultural difference in mate preference as opposed to livestock breeding practices would be a clear sign that some other factor is judged more important in mating than famine survival value. My hypothesis is offspring qualities. This hypothesis might also be testable on the basis of other observable qualities, such as intelligence, personality, and facial proportions.
Ember et al. (2005:266) end their paper with a discussion of changing female fatness preferences in the United States:
In the United States, shifts towards valuing thinness versus fatness seem to have coincided with the rise of women's movements in the 1920s and late 1960s. Consider that Marilyn Monroe epitomized beauty in the 1950s; she was well-rounded, not thin. "Thin" became more popular when people (particularly women) began to question early marriage and staying home to be mothers of large families. They appear to have rejected male chivalry and preferred men who were sensitive and caring. (Dennis Werner, personal communication, suggested this argument.) Was machismo behavior also less acceptable at those times? We suggest that it was, particularly among intellectuals and the elite. Whether and how these changes are causally connected require further investigation.
This seems like a roundabout way of saying that style equals success. Are human biologists studying attractiveness missing the nose on the face of the issue?
References:
Brown, PJ and Konner M. 1987. An anthropological perspective on obesity. Ann New York Acad Sci 499:29-46.
Ember CR, Ember M, Korotayev A, de Munck, V. 2005. Valuing thinness or fatness in women: reevaluating the effect of resource scarcity. Evol Hum Behav 2:257-270. ScienceDirect
Attractive women have high estrogen?
This BBC story covers this paper (warning! PDF!) that found a correlation (r = 0.48) between attractiveness and estrogen level in women:
The findings make evolutionary sense - men are attracted to the most fertile women, the University of St Andrews team told a Royal Society journal.
Oestrogen levels during puberty can impact on appearance by affecting bone growth and skin texture, they said.
...
The team of psychologists at the University's Perception Lab photographed 59 young women's faces aged between 18 and 25 and analysed their sex hormone levels.
They then asked 30 volunteers - 15 male and 15 female - to rate the faces according to attractiveness.
Both male and female volunteers rated the faces of the women with the highest hormone levels as the most attractive.
My first reaction was that it just seems so...unlikely.
My more studied reaction is that I'm not sure that the results are as interesting as they look at first glance. The paper is conservative in its interpretations -- much more so than the comments in the BBC article would suggest.
The general idea is that males want to be able to assess female fertility, and if they can "read" estrogen levels through facial characteristics (which they perceive as "attractiveness") then it should have been adaptive.
This argument would have to be based on two correlations: a correlation between "attractiveness" and estrogen level during facial development, and a correlation of estrogen level during facial development and fertility. This paper reports the first of the two.
The second is (as far as I know) unknown, although there may be some hints in the opposite direction. There is this paper for example, describing the effect of estrogen treatment to reduce final stature in tall girls (estrogen promotes early epiphyseal fusion):
Fertility problems were more prevalent in women previously given estrogens to lessen their adult height....Among women attempting to become pregnant for the first time, the likelihood of conceiving every month was much lower for treated than for untreated women ( Fig. 1). Women treated for tall stature had a significantly lower age-adjusted per-cycle rate of conceiving a first pregnancy. Fecundability was impaired both in women treated with DES and those given EE, and the timing of treatment (before or after menarche) and its duration did not influence the findings.
It seems to me that if pubertal estrogen levels influence fertility, the strongest effect should be on the age at menarche -- since that influences the reproductive lifespan.
Menarche would be a much more important reason for men to be able to assess estrogen levels in developing women. In small human groups, most men probably would have had a very good knowledge of all the women who would be potential mates. Attractiveness might have made some considerable difference to mating decisions, but these would also have been subject to many other constraints. On the other hand, it would be of great value to be able to accurately assess when new maturing young women would become available to mating. A young woman would likely be well-served to provoke some competition between males. Signaling maturity through physical changes would be a way to spur this competition -- which in many cases would have played out over many months or even years.
A major influence on age at menarche is fatness, and fatness is related to estrogen levels in older women (Kaplowitz et al. 2001). Fatness may also significantly affect assessments of attractiveness, although not in an obvious way. I would guess that a slightly fuller face would be generally regarded as more "feminine", and in the study "feminine" ratings were correlated (r=0.97) with attractiveness. Certainly the average physiognomy of the 10 high-estrogen women in their sample has a fuller face than the average of the 10 low-estrogen women:
Left: 10 highest-estrogen average face. Center: 10 lowest-estrogen average. Right: Actress Lindsay Lohan giving come-hither look.
On the other hand, facial fullness -- especially in the lower face -- may not be a good guide to fatness generally. It's all just so confusing!
The pictures do give a good hint to the "make-up effect" that the article discusses:
"The findings about make-up are also interesting. The implication is that women are employing a deceptive strategy. They can fool the male visual system with make-up."
Yeah. They appear to fool "love bugs", too.
Making cooperation happen
James Fowler (UC Davis) has an article in the May 10 PNAS that presents a model explaining the benefits that may arise from "altruistic punishment." In this model, people can punish "free riders" in games in which public goods are available, but in order to impose punishment, the punishers themselves must pay a cost. If a punisher were strictly guided by his or her own interest, we might predict that they would tolerate free riders (at least to some extent) rather than pay a cost themselves to punish them.
The analogy with ordinary (i.e. non-game-related) social behavior in humans is fairly straightforward. It's the same problem faced by Jimmy Stewart in The Man Who Shot Liberty Valance. It clearly is better for the territory for Liberty to be killed. But anyone who steps up to do it is pretty likely to end up dead himself. By standing up to the outlaw, Stewart becomes an altruistic punisher: he is willing to accept a stiff cost in order to impose a penalty on the free rider. On the other hand, if he knew that John Wayne had his back, he would have been a non-altruistic punisher.
To demonstrate the potential of the altruistic punisher as a strategy, Fowler sets up a model society without them. In this society, the model interactors may contribute to cooperative activities, they may defect by taking the benefits without paying the cost, or they may simply decide not to participate, preferring to go it alone rather than pay for benefits that are ultimately stolen by defectors. Then, altruistic punishers are introduced into the society.
Fowler proceeds to test the boundaries of this strategy and the conditions under which it can spread. He finds that some combinations of costs and rewards can allow this strategy to completely dominate a population. Some of the interesting aspects of this strategy are that it reduces the amount of information interactors must have to punish effectively, in comparison with models that use a "reputation" or "standing" as a mediator for recognizing good cooperators. Another interesting aspect is that interactors need to coordinate their actions within groups for cooperative behaviors to persist:
To conclude, this model has several important implications. First, it shows how altruistic punishment can emerge in a population in which there is both an incentive not to contribute and an incentive not to punish noncontributors. Past work has shown that punishment strategies can persist under these conditions, but it has relied on group selection to explain how such prosocial strategies might evolve. In constrast, this model demonstrates that both the origin and persistence of widespread cooperation is possible with voluntary, decentralized, anonymous enforcement, even in very large populations under a broad range of conditions.
Second, the model suggests that the cycle of cooperation, defection, and nonparticipation recently identified by scholars is important for understanding the origin of cooperation but may not be useful for understanding its persistence. When altruistic punishment evolves, the cycle should disappear and cease to be observed in the population dynamics.
I like the last conclusion the best, because it directly relates to the common conception of punishment strategies in social interactions:
Last, the model questions a "folk theorem" result, which indicates that punishment strategies can enforce any other strategy, even those that yield a payoff disadvantage. Note that when participation is optional, punishers can evolve and persist only if they yield a payoff advantage b - c > sigma to the population. Thus, the model suggests that there are restrictions on what kinds of strategies punishment can enforce.
Of course any rational person knows this must be true. Any brutal despot may retain power if he exerts only a small cost on the vast majority of people. But if the cost becomes onerous beyond a point, the despot is like Liberty Valance: the people will rise up. The cost of altruistic punishment will be less, for many, than the cost of the continued tolerance of the despot. That is why one of the most important tools of the despot is psychologically isolating people from each other. This isolation makes people unaware that their neighbors are arriving at the same cost-benefit analysis that they are themselves. The realization that everyone has come to the same conclusion about the tyrant radically reduces the cost of resistance, by making it clear that the risk of individual punishment is much lower than they may have thought. It is then that revolutions happen.
The same is doubtless true in smaller-scale social groups, like the frontier towns in so many Westerns. The best example is The Magnificent Seven. The villagers pool their money to hire the professional gunmen, but we see a lot of reluctance and doubt among them when Yul Brynner and his buddies arrive. But the early success of Bronson, Coburn, and company show the benefits of their strategy to the village. Before long, the "altruistic punisher" strategy has spread to all the able-bodied men, and they succeed in fighting off Eli Wallach and his bandits.
It means something that all of our stories have these kinds of interactions in them. I usually tell my students that "Survivor" is a great way to see human social interactions in action. But I think in this case "Survivor" makes a bad analogy, because it is so short-term; there is no chance for the little society to reach an equilibrium. The Western is a much better model for these kinds of interactions, because the entire premise of a good Western is a microcosm of society that is out of balance in the beginning. The hero has to find a way to return the balance, which usually involves an act of self-sacrifice for the greater good. The ultimate altruistic punisher.
References:
Fowler JH. 2005. Altruistic punishment and the origin of cooperation. Proc Nat Acad Sci USA 102:7047-7049. PNAS Online
Genes and politics
Usually that's a title about something related to cloning or stem cells or something. But in this case, it's about the fact that your vote may be heritable! I'm posting this because I just lectured about heritability last week. Like usual, I noted that political affiliation exhibits strong familial effects, but that these are mostly due to shared environment and not genetic variance.
Little did I know that a new study would show that genes do play a substantial role. In a twin study that numbered over 8,000 sets of twins, researchers asked questions about political hot-button topics and general political preferences.
On school prayer, for example, the identical twins' opinions correlated at a rate of 0.66, a measure of how often they agreed. The correlation rate for fraternal twins was 0.46. This translated into a 41 percent contribution from inheritance.
As found in previous studies, attitudes about issues like school prayer, property taxes and the draft were among the most influenced by inheritance, the researchers found. Others like modern art and divorce were less so. And in the twins' overall score, derived from 28 questions, genes accounted for 53 percent of the differences.
But after correcting for the tendency of politically like-minded men and women to marry each other, the researchers also found that the twins' self-identification as Republican or Democrat was far more dependent on environmental factors like upbringing and life experience than was their social orientation, which the researchers call ideology. Inheritance accounted for 14 percent of the difference in party, the researchers found.
And then there's this:
A mismatch between an inherited social orientation and a given party may also explain why some people defect from a party. Many people who are genetically conservative may be brought up as Democrats, and some who are genetically more progressive may be raised as Republicans, the researchers say.
So political party membership may not be strongly heritable, but the tendency to defect, given a conflict with the parental party, may be.
Much more good stuff in the article, including the speculation that the country may become increasingly polarized.
Imaging genomics
I'm noticing a lot of new uses of the word "genomics" in the last few days. I'm guessing that it's the new way to spice up grant applications.
"Genomics" doesn't really have a meaning different from "genetics", except that it usually means more than one locus. It seems to come in most often when people are using microarrays to characterize a large set of SNPs. In that case, you can kind of imagine it as "genetics + computers - laboratory".
But the "imaging genomics" story isn't really a multiple locus exercise, it just seems to be an MRI study of people with known genotypes for one gene, in this case MAO-A. I picked this NIH press release up from Science Blog:
A version of a gene previously linked to impulsive violence appears to weaken brain circuits that regulate impulses, emotional memory and thinking in humans, researchers at the National Institutes of Health's (NIH) National Institute of Mental Health (NIMH) have found. Brain scans revealed that people with this version - especially males - tended to have relatively smaller emotion-related brain structures, a hyperactive alarm center and under-active impulse control circuitry. The study identifies neural mechanisms by which this gene likely contributes to risk for violent and impulsive behavior through effects on the developing brain.
...
"These new findings illustrate the breathtaking power of 'imaging genomics' to study the brain's workings in a way that helps us to understand the circuitry underlying diversity in human temperament," said NIH Director Elias A. Zerhouni, M.D., who conducted MRI studies earlier in his career.
So I figure when the head of NIH is talking about it, it must be the new buzzword.
Several previous studies had linked increased serotonin during development with violence and the L version of MAO-A. For example, a 2002 study by NIMH-funded researchers discovered that the gene's effects depend on interactions with environmental hard knocks: men with L were more prone to impulsive violence, but only if they were abused as children. Meyer-Lindenberg and colleagues set out to discover how this works at the level of brain circuitry.
Using structural MRI in 97 subjects, they found that those with L showed reductions in gray matter (neurons and their connections) of about 8 percent in brain structures of a mood-regulating circuit (cingulate cortex, amygdala) among other areas. Volume of an area important for motivation and impulse regulation (orbital frontal cortex) was increased by 14 percent in men only. Although the reasons are unknown, this could reflect deficient pruning - the withering of unused neuronal connections as the brain matures and becomes more efficient, speculates Meyer-Lindenberg.
There's more to the study, in PNAS, including increased reactivity in the amygdala and hippocampus.
The thing I always worry about in these imaging studies is that they don't give a good impression of the variation in each sample. Sure, there may be a mean difference between them, but how great is that mean difference compared to the variation within each group? But that's just my pet peeve.
It's amazing we've come to the point where we genotype people, put them into a scanner, and check out anatomical and functional differences in their brains. But still, the hypotheses raised here are developmental hypotheses, and to test them we have to look at development. So far, and yet so far to go.
Inheritance of abuse in rhesus macaques
Dario Maestripieri (U of Chicago) has a paper in PNAS demonstrating the transmission of abusive parenting style from mothers to their offspring in macaques. The abstract:
Maternal abuse of offspring in macaque monkeys shares some similarities with child maltreatment in humans, including its transmission across generations. This study used a longitudinal design and a cross-fostering experiment to investigate whether abusive parenting in rhesus macaques is transmitted from mothers to daughters and whether transmission occurs through genetic or experiential factors. Nine of 16 females who were abused by their mothers in their first month of life, regardless of whether they were reared by their biological mothers or by foster mothers, exhibited abusive parenting with their firstborn offspring, whereas none of the females reared by nonabusive mothers did. These results suggest that the intergenerational transmission of infant abuse in rhesus monkeys is the result of early experience and not genetic inheritance. The extent to which the effects of early experience on the intergenerational transmission of abusive parenting are mediated by social learning or experience-induced physiological alterations remains to be established.
I think that nongenetic inheritance of behaviors is a very important, and usually underestimated, source of variation in survival and reproductive success. In mammals especially, individuals learn much from their mothers. Foraging strategies are the most obvious learned behaviors, but parenting styles are perhaps equally important. "Good" mothers can be expected to have more healthy offspring, who should be better prepared for interactions in social groups, and ultimately better able to raise their own offspring well.
The hard question is, what is good? Outcomes of individuals pursuing different parenting strategies are difficult to assess. In particular, in this case it might seem intuitive that the abusive parents would reduce the fitness of their offspring. But primates experience a range of stresses in social interactions, so it is not so easy to predict whether a particular kind of maternal abuse will further compound the negatives. Perversely, it might help prepare the juvenile for stresses later in life, or insulate them against stresses from other individuals. We just don't know. It could be that abuse is a short-term dysfunction that naturally would disappear, or it could be that it is an alternative evolutionary strategy that persists at some frequency in natural populations. Telling the difference would require observing natural populations for many generations
This pattern of inheritance is not usually considered to be cultural. Indeed, Maestripieri notes that he doesn't even know whether it is learned. An alternative is that it is a manifestation of innate psychological mechanisms after exposure to a childhood stressor, which may not be unreasonable since the exposure begins so early in infancy (within the first month after birth). But it has implications for the evolution of social learning and culture. Fitness differences that stem from learning ultimately must underlie the evolution of cultural capacities. The mind has patterns that make such learning possible, and these patterns are themselves complex adaptations.
So for the origins of culture from the initially noncultural, relatively complex inherited behaviors like this one may make a template with some predictable features.
References:
Maestripieri D. 2005. Early experience affects the intergenerational transmission of infant abuse in rhesus monkeys. Proc Nat Acad Sci USA 102:9726-9729. Full text online
In oxytocin we trust
It is essential to commencing labor contractions in pregnant women. It is implicated in behaviors related to maternal care, including milk letdown. It apparently helps to regulate social relationships in primates and other mammals.
And now, according to a study in Nature by Michael Kosfeld and colleagues (2005), oxytocin appears to be related to trust between people.
From the abstract:
Here we show that intranasal administration of oxytocin, a neuropeptide that plays a key role in social attachment and affiliation in non-human mammals causes a substantial increase in trust among humans, thereby greatly increasing the benefits from social interactions. We also show that the effect of oxytocin on trust is not due to a general increase in the readiness to bear risks. On the contrary, oxytocin specifically affects an individual's willingness to accept social risks arising through interpersonal interactions. These results concur with animal research suggesting an essential role for oxytocin as a biological basis of prosocial approach behaviour (Kosfeld et al. 2005:673).
Neuroscientist Antonio Damasio wrote an accompanying editorial.
There is also a story in the Economist on the paper. Damasio summarizes the logic of the conclusions:
Kosfeld et al. provide an engaging discussion of the possible mechanisms behind their finding. They reject the possibility that oxytocin has a nonspecific positive effect on social behaviour, because of its different influence on investors and trustees. Approach and trust possibly dominate the behaviour of investors, and that is where oxytocin works, whereas trustee behaviour is dominated by a principle of reciprocity, for which oxytocin seems irrelevant. Kosfeld et al. also reject the possibility that oxytocin merely reduces the sensitivity to risk, because in a control experiment in which the investors knew the trustee was a computer, they did not take any extra risks. The authors finally settle for an attractive pair of factors: that oxytocin overcomes the aversion to betrayal (which applies only to the investors), and that this is combined with the effects of reward that result from enhanced approach behaviour (Damasio 2005:571).
Damasio also points to some pretty interesting hypotheses about well-known pathologies, including autism and William's syndrome. The first is characterized by a relative lack of social bonding and trust; William's syndrome patients "approach strangers fearlessly and indiscriminately." He raises the question of whether this level of trust may come from excessive oxytocin release. One may alternatively ask whether it comes from an alteration in the underlying neural structures affected by oxytocin, but whether it is the first of the second, it seems likely that the trust-related mechanisms of the brain require both a structural and neurochemical input.
There has been a recent spurt of research on genes that may influence the structure or size of the brain, and their pattern of evolution in humans. These genes demonstrate the kinds of changes that may have generated the structural circuitry that underlies human behavior, although their workings are at present nearly completely unknown. But the influence of oxytocin on many aspects of human behavior illustrates an alternative route for the influence of genetic evolution. Oxytocin has multiple roles as a hormone, neuropeptide, and neurotransmitter. Instead of directly influencing the architecture of the brain, it may strongly modulate the functions of structural elements by predisposing or biasing certain kinds of outputs. Much remains to elucidate oxytocin's role, as well as that of other neuropeptides. But this kind of modulation makes it clear that the architecture of the brain must be adapted to work via the mediation of such molecules -- almost as if there were a "register shift" in the activity of certain neural substructures in response to the activity of these neuropeptides. Human brains differ from those of other primates not merely in their blueprint but also in their supply chain, as it were.
The research also points to the existence of strong subconscious influences on what might be classified as "rational" decision-making. This demonstration is not new, but it resonates as one that confounds more traditional analysis of human social bonds. Reciprocity is often conceptualized as a relation built on repeated interactions leading to trust. Humans are generally depicted within this framework as rational decision-makers who can examine their past history with other individuals (or make use of such information donated to them by other, known, individuals) and structure their future interactions accordingly. The role of oxytocin suggests that such decisions are not entirely, or perhaps even principally, made consciously. This is not to say that humans fail to make rational decisions, but instead to suggest that we have strong innate biases that reinforce certain kinds of decisions and weaken others.
Damasio's most interesting comments are in his last paragraph:
Some may worry about the prospect that political operators will generously spray the crowd with oxytocin at rallies of their candidates. The scenario may be rather too close to reality for comfort, but those with such fears should note that current marketing techniques -- for political and other products -- may well exert their effects through the natural release of molecules such as oxytocin in response to well-crafted stimuli (Damasio 2005:572).
In other words, all those pictures of babies on toilet paper advertisements are manipulating your trust. Or is that the babes in beer ads?
References:
Damasio A. 2005. Human behaviour: brain trust. Nature 435:571-572. Nature online
Kosfeld M, Heinrichs M, Zak PJ, Fischbacher U, and Fehr E. 2005. Oxytocin increases trust in humans. Nature 435:673-676. Nature online
Animal cognition minireview
If you get Science, there's a pretty good News Focus item by Elizabeth Pennisi describing recent experiments on animal social intelligence. The background is a little thin, but it is a good overview of recent work, on many different species.
Those studies are beginning, and by looking across the animal kingdom, researchers are gleaning the conditions that predispose a species toward social intelligence. For example, Kay Holekamp, an ethologist at Michigan State University in East Lansing, has observed hyenas for 18 years and concludes that these scavengers can recognize not just their own status relative to the pack leader but also the status relationships of other pack members. Other researchers are trying to measure social intelligence, albeit often in indirect ways, in ungulates, elephants, and dolphins. And in this week's issue of Current Biology, researchers demonstrated that fringe-lipped bats learn to listen for unfamiliar prey from fellow bats.
You do get a flavor of the difficulty of testing cognitive information in nonlinguistic animals, with many clever solutions in experiments. This, for instance, is a study I would not want to participate in:
For example, in a new study in Cognition, Hare and his colleagues designed another competition over food. They had chimps go head-to-head against a human who pulled food out of reach as a chimp went to grab it. If the chimps were given the option, they sneaked up behind a barrier to get to the food instead of approaching it directly. Thus, the chimps demonstrated not only that they knew what the human could see but also that they knew how to manipulate the situation to stay out of sight.
I don't do this kind of thing with my children more than once, and they don't have giant canine teeth.
And there is a note of skepticism:
Galef is particularly skeptical of researchers who have concluded that chimps respond to peer pressure, that wolves and capuchin monkeys have a sense of fairness, or that jackdaws are the avian equivalent of the Good Samaritan. "It's gotten a little out of hand," he complains. And not one species has yet passed the falsebelief test, he points out.
It is really hard to avoid a Clever Hans effect in some of this work -- subtle cues that animals may use that humans cannot pick up on. And the article points that out. It's a good short read on behavior.
Cooperation through repression
I've been meaning to write about the paper on primate policing by Jessica Flack and colleagues.
Using 'knockout' experiments on a large, captive group of pigtailed macaques (Macaca nemestrina), we show that a policing function, performed infrequently by a small subset of individuals, significantly contributes to maintaining stable resource networks in the face of chronic perturbations that arise through conflict. When policing is absent, social niches destabilize, with group members building smaller, less diverse, and less integrated grooming, play, proximity and contact-sitting networks. Instability is quantified in terms of reduced mean degree, increased clustering, reduced reach, and increased assortativity. Policing not only controls conflict, we find it significantly influences the structure of networks that constitute essential social resources in gregarious primate societies. The structure of such networks plays a critical role in infant survivorship, emergence and spread of cooperative behaviour, social learning and cultural traditions.
The paper cites a review by Steven Frank titled, "Repression of competition and the evolution of cooperation." From the abstract:
Repression of competition within groups joins kin selection as the second major force in the history of life shaping the evolution of cooperation. When opportunities for competition against neighbors are limited within groups, individuals can increase their own success only by enhancing the efficiency and productivity of their group. Thus, characters that repress competition within groups promote cooperation and enhance group success. Leigh first expressed this idea in the context of fair meiosis, in which each chromosome has an equal chance of transmission via gametes. Randomized success means that each part of the genome can increase its own success only by enhancing the total number of progeny and thus increasing the success of the group. Alexander used this insight about repression of competition in fair meiosis to develop his theories for the evolution of human sociality. Alexander argued that human social structures spread when they repress competition within groups and promote successful group-against-group competition.
In this way, Frank explicates the suppression of competition as a classic multilevel selection problem -- comparable to the problem of meiotic drive vs. meiotic fairness, in which chromosomes are selected for their fitness effects at the organismal level because there is no possibility for them to compete at their own level.
The paper opens with a great quote by Richard Alexander:
The function of laws is to regulate ... the reproductive strivings of individuals and subgroups within societies, in the interest of preserving unity in the larger group. ... Presumably, unity in the larger group feeds back beneficial effects to those ... that propose, maintain, adjust, and enforce the laws (Alexander 1979:240).
This raises a question: what are the beneficial effects of policing for the policer that outweigh its costs? Is it true, for instance, that they have more reproductive opportunities? Or that their efforts benefit their likely offspring?
Here is a prediction from Frank:
Repression of competition therefore contributes an immediate benefit to the group, enhancing the reproductive success of those that invest in policing selfish neighbors. Repressing selfish neighbors imposes a direct cost on those that police, thus policing spreads only when the beneficial effects of improved group success flow back to the policing individuals and their kin.
Policing increases from zero when r < 1 - c, where r is the relatedness of an individual to its group and c is the cost to an individual for investing its resources in policing. Note that low relatedness favors policing. When relatedness is high, selection favors self-restraint and cooperation without the need for policing by neighbors. As relatedness declines, selfishness tends to increase, causing a drop in group efficiency and the average success of each group member. Under conditions of poor group efficiency, policing increases because it enhances the quality of life and the success of those that police.
Now this is interesting. Policing can have the same effect as kin selection, in groups where the average relatedness of individuals is low. Its effect will be greater where the cost of policing is low.
But the Nature paper doesn't really discuss the issue of cost for the policer. It merely documents the social disruption that comes from "knocking" the policers out of the group.
In another 2005 paper in American Naturalist, Flack and colleagues discuss the issue of cost more directly. They begin by asserting that primate policing may be costly because it "requires intervention by third parties into ongoing contests." This entails the risk that one of the parties will attack the policer.
Yet, there are no quantitative data on the costs of policing, in terms of aggression received, to policers in primate or other mammalian species. Furthermore, although there are few quantitative data on the incidence of policing in primates, it appears that effective policing occurs in one-male groups, including gorillas (Gorilla gorilla; Watts et al. 2000) and golden monkeys (Rhinopithecus roxellanae; Ren et al. 1991), but, with the exception of chimpanzees (de Waal 1982), is rare in hierarchical multimale, multifemale societies (de Waal 1977; Ehardt and Bernstein 1992; Petit and Thierry 2000) like those of macaques and baboons. It is not understood why this is the case.
They develop the model that the effectiveness of policing is a function of power gradients -- single-male groups concentrate the power in one individual and allow lower-cost policing.
But their observations of pig-tailed macaques show that many of the most frequent policers are females, including one of the most effective ones. That seems to go against the single-male policing idea.
And there is this point:
Mathematical models of policing and of related intervention behaviors such as punishment are able to effectively reduce their number of state variables by assuming that all individuals pay the same cost for engaging in conflict management or repressing competition. Although this is a reasonable simplifying assumption, it makes the evolution of policing appear more difficult or improbable than actually seems to be the case. There is good evidence from the study of dominance relationships in animal societies for individual variation in resource holding potential or vigor (Clutton-Brock and Parker 1995) and, from this study, for individual variation in power. By allowing for variation in state, Frank (1995, 1996) has shown that small differences in individual vigor can lead to large variations in individual contributions to policing when relatedness is low. The claim that variation in individual vigor is related to variation in investment in conflict management requires the additional assumption that the cost of conflict management varies inversely with individual state. One of the findings of this study is that cost is not only a function of the individual intervening but also of the power values of the individuals engaged in the dispute. Thus, variation in individual vigor is not sufficient. A power structure must arise in which individuals also vary in the degree to which group members perceive them capable of successfully using force. It would be interesting to extend the Frank (2003) treatment to include this assumption.
Heterogeneity is what makes all these things complex to model mathematically. It's also why the Santa Fe Institute is interested in this kind of problem in social structure.
The social disruption resulting from lack of policing is interesting in its own right. The Nature study finds that the average level of aggressive interactions increases, the number of affiliative or reconciliatory behaviors (like grooming) decreases. The conclusion is the critical paragraph:
Conflict threatens to destabilize society. Its immediate consequences include injuries and damaged relationships. It has been demonstrated that policing can directly prevent this. We find that policing also has far-reaching indirect consequences, significantly altering construction of social resource networks that make group living advantageous. We demonstrated this by analysing changes to four network properties. We observe that when policing is operational, group members build larger social networks characterized by greater partner diversity and increased potential for socially positive contagion and cooperation. Without policing, high conflict frequency and severity leads to more conservative social interactions and a less integrated society. Mechanisms for buffering frequent conflicts are therefore essential for construction of stable social niches upon which individuals depend for behavioural resources.
What exactly is the problem with society being destabilized? One might speculate that the worst possible outcome is that different cliques of individuals will break apart into smaller groups -- in other words, the presence of policing enables the individuals to live in a larger group than would be possible without it. That might be a suboptimal solution for other reasons. For example, larger groups ought to carry some protection from predation. But many primates live in small groups anyway.
So are the policers an integral element of primate societies, or an emergent phenomenon more or less natural within large groups? In the latter case, policing might make some difference at an unstable boundary between stable, small group size and large groups that might break down without it.
If this were true, there would be no need to see policers as particularly selected for their function in group selection. Instead, there is a much simpler hypothesis: if the effect of policers is to maintain larger groups (at least in some cases), then policers are directly increasing their own mating opportunities (by keeping more females near them).
But that doesn't address why females would police. One idea about it would be that females face costs both ways. There is a cost to policing, but there is also a cost to living in a society without police. For females, this may come down to safety for offspring -- when aggression increases, juvenile mortality may increase with it.
This kind of behavioral variation might well be able to be studied in the wild. Behavioral traditions within groups probably lead to great heterogeneity -- especially if the number of policers in any given group is low. Some groups will have more aggressiveness than others, and juvenile survivorship may track that.
References:
Flack JC, Girvan M, de Waal FBM, Krakauer DC. 2006. Policing stabilizes construction of social niches in primates. Nature 439:426-429. Full text (subscription)
Flack JC, de Waal FBM, Krakauer DC. 2005. Social structure, robustness, and policing cost in a cognitively sophisticated species. Am Nat 165:E126-E139. Full text
Frank SA. Perspective: repression of competition and the evolution of cooperation. Evolution 57:693-705. PubMed
Snakes on the brain
Well, it hit Slashdot, so here goes:
Snakes as agents of evolutionary change in primate brains
Lynne A. Isbell
The abstract is really long. I'm going to quote all of it, but I'm separating into sections and adding numbers [in brackets] for further comment:
[1] Current hypotheses that use visually guided reaching and grasping to explain orbital convergence, visual specialization, and brain expansion in primates are open to question now that neurological evidence reveals no correlation between orbital convergence and the visual pathway in the brain that is associated with reaching and grasping. An alternative hypothesis proposed here posits that snakes were ultimately responsible for these defining primate characteristics.
In other words, you can reach and grasp with one eye closed. More below.
[2] Snakes have a long, shared evolutionary existence with crown-group placental mammals and were likely to have been their first predators.
Opportunity.
[3] Mammals are conservative in the structures of the brain that are involved in vigilance, fear, and learning and memory associated with fearful stimuli, e.g., predators. Some of these areas have expanded in primates and are more strongly connected to visual systems. However, primates vary in the extent of brain expansion. This variation is coincident with variation in evolutionary co-existence with the more recently evolved venomous snakes. Malagasy prosimians have never co-existed with venomous snakes, New World monkeys (platyrrhines) have had interrupted co-existence with venomous snakes, and Old World monkeys and apes (catarrhines) have had continuous co-existence with venomous snakes.
Not obvious that brain expansion and conservative fear pathways are really related to each other. Since there are many interconnections between different brain regions, it is not at all persuasive that some of the brain areas connected to fear response and learning are connected to neocortical areas that evolved within primates.
[4] The koniocellular visual pathway, arising from the retina and connecting to the lateral geniculate nucleus, the superior colliculus, and the pulvinar, has expanded along with the parvocellular pathway, a visual pathway that is involved with color and object recognition. I suggest that expansion of these pathways co-occurred, with the koniocellular pathway being crucially involved (among other tasks) in pre-attentional visual detection of fearful stimuli, including snakes, and the parvocellular pathway being involved (among other tasks) in protecting the brain from increasingly greater metabolic demands to evolve the neural capacity to detect such stimuli quickly.
Interesting...although the connection to snakes ("fearful stimuli, including snakes") isn't exclusive.
[5] A diet that included fruits or nectar (though not to the exclusion of arthropods), which provided sugars as a neuroprotectant, may have been a required preadaptation for the expansion of such metabolically active brains.
Possibly true, no obvious snake influence.
[6] Taxonomic differences in evolutionary exposure to venomous snakes are associated with similar taxonomic differences in rates of evolution in cytochrome oxidase genes and in the metabolic activity of cytochrome oxidase proteins in at least some visual areas in the brains of primates.
Interesting. But the number of primate lineages compared is only three (anthropoids before platyrrhine/catarrhine divergence, and platyrrhines vs. catarrhines after divergence). And the same relation could be explained in terms of brain size alone (if larger brained lineages need greater COX activity).
[7] Raptors that specialize in eating snakes have larger eyes and greater binocularity than more generalized raptors, and provide non-mammalian models for snakes as a selective pressure on primate visual systems.
I wonder why this is -- does it have to do with the motion patterns of snakes compared to other raptor prey (like quick-moving small mammals)? Or the shape and coloration of snakes against likely backgrounds?
[8] These models, along with evidence from paleobiogeography, neuroscience, ecology, behavior, and immunology, suggest that the evolutionary arms race begun by constrictors early in mammalian evolution continued with venomous snakes. Whereas other mammals responded by evolving physiological resistance to snake venoms, anthropoids responded by enhancing their ability to detect snakes visually before the strike.
Unanswered questions
I have to say, I approached this one very skeptically, but after reading it I have a lot of sympathy for the approach. But to start off, I will be very clear about questions that someone might reasonably ask that the paper really doesn't have great answers for:
Are primates really under that much predation from snakes? Venomous snakes in particular? Most primates are pretty big to be the intended prey of venomous snakes, after all...The paper devotes a section to this question. There have been some observed or suspected instances of snakebite in wild primates, and humans suffer a lot of snakebite -- especially in the tropics. But there just aren't any good numbers, such as relative importance of snakes compared to other predators or mortality risks.
My own feeling about this is that snakes probably are a significant risk to wild primates, but that they are one of many such risks. So the question is whether selection favored effective responses to snakes in particular or instead responses to many predation risks in general.
Distinguishing general from particular is a pretty hard problem -- most of the visual pathways discussed in this paper are useful for detecting all kinds of things, not merely snakes. For example, the paper includes this:
With its emphasis on object recognition, the P pathway would have initially helped those with a diet of fruits, flowers, and nectar to locate foods (and perceive snakes and other salient objects near them). Later, with its emphasis on color, the P pathway would have helped such primates locate foods with the highest levels of sugars (Sumner and Mollon, 1996), thereby more effectively protecting the expanding brain against excitotoxicity.
Or, maybe finding fruits just happened to help evade likely predators including snakes. In other words, there may be a link, but the direction of causation is far from clear.
Can coevolution with snakes really explain large patterns of evolution across the primate order? I mean, sure, maybe living primates have some snake-evasion responses, and better vision would help avoid snakes, but we're talking about the Paleocene here...All overarching single-cause hypotheses face this problem: the things they want to explain almost always happened at different times. Here, we have the evolution of larger brains and arboreality early in the Cenozoic (or even the Cretaceous), the evolution of the visual system through the Eocene and Oligocene, the evolution of brain size in different catarrhine lineages during the Oligocene and Miocene, and so on. This paper plays that problem as a strength: snakes plausibly exerted a mortality pressure across all those time intervals, when other hypotheses like nocturnal insect hunting didn't apply to most of them. On the other hand, nocturnal insect hunting doesn't really try to explain later events. A single grandiose over-arching hypothesis may claim a strength that it explains more things, but that is no substitute for testing each of its components. The relationships proposed here are plausible, but few of them admit any ready tests.
So those are some problems for the hypothesis that the paper really doesn't answer well. It might well be that snakes really were such an important mortality risk that ancient primates had adaptations specially to defend against them, and that those adaptations themselves contributed to later primate evolution. But it's not easy to sort out the causes -- maybe those apparent "snake-adaptations" were really initiated for other purposes and happen to be useful for resisting snakes, or maybe they really don't have much to do with snakes one way or the other.
Stuff I liked
But there's lots of clever stuff in this paper, making surprising connections between visual processing, diet, and predation risk. For example, I like this:
The hypothesis that constricting snakes favored larger brain size via greater visual specialization in primates identifies a diet of ripe fruit or nectar as a requirement for, and as a cause of, visual specialization and brain enlargement, but not as the ultimate cause. Recall that high CO [cytochrome oxidase] activity reflects high levels of neuronal metabolic activity and that brains are highly metabolically active tissues. Heightened CO activity is, however, potentially costly in that it can lead to excitotoxicity and neuronal death (Lucas and Newhouse, 1957, Olney, 1969, Olney, 1990, Choi, 1988 and Meldrum and Garthwaite, 1990) without protection against overexposure to glutamate, the main excitatory neurotransmitter in the central nervous system (Orrego and Villanueva, 1993). Glutamate is an amino-acid derivative of glucose (Feldman et al., 1997: 392), and it has widespread effects on the brain. Of particular relevance here is its ability to enhance fear-related learning in the amygdala (Walker and Davis, 2002) and to enhance learning in color discrimination tasks (Popke et al., 2001).
Overexposure to glutamate can be minimized by eating glucose, a sugar found in flowers and ripe fruit (Henneberry, 1989, Romano et al., 1993 and Guyot et al., 2000). If frugivores indeed have larger brains and higher basal metabolic rates than folivores or insectivores of the same body size (Clutton-Brock and Harvey, 1980, Armstrong, 1983, Barton et al., 1995 and Martin, 1996), the difference could be a result of the neuroprotectant property of glucose, obtained from a diet of fruits and flowers.
It seems like fruit-seeking behavior would be adaptive for a primate that maintained high cytochrome oxidase levels, not only globally but in local brain regions (here, the visual system is the focus, but possibly other regions might be implicated). People tend to take for granted that sugar-rich foods would be good for primates, but that is really not obvious -- fruits tend to have low protein levels, for example. So an evolutionary specialization on fruits has costs, and it is important to sort out how and why early primates bore those costs.
The paper has a really good section (called "Frequently asked questions!") that presents strong critiques of a couple of oft-cherished theories of primate evolution. It argues that the "nocturnal visual predation" hypothesis is weak because there is evidence that the key primate characteristics ("orbital convergence, enhanced vision, grasping hands and feet, nails, and large brains") did not evolve together.
And I love this paragraph in the "What about sociality" section:
First, [the social intelligence hypothesis] must explain why sheep (Ovis aries), which are not known for having large brains, are still able to visually recognize and remember as many individuals as there are in a typical baboon group, even after a year of separation (Kendrick and Baldwin, 1987 and Kendrick et al., 2001). In both primates and sheep, the temporal cortex is a major site of facial recognition and memory (Gross et al., 1972, Damasio et al., 1982, Perrett et al., 1992, Kanwisher et al., 1997 and Kendrick et al., 2001).
This is a telling sentence:
Critics of the inclusiveness of this [snake] hypothesis are challenged to explain why it would be easier, or more likely, for primates to evolve large bodies or large, complex groups in response to predators than to modify the mammalian visual system in response to the same threat.
There has been a lot more attention to the evolution of brain size, body size, and group size, and comparatively little to the evolution of the visual system (aside from color). Primates have long life spans compared to other mammals, which means that primates have low average mortality rates as adults. One way to get low mortality is to maximize avoidance of predators. To the extent that large brains facilitate evading predators, they will be correlated with low adult mortality. To the extent that large social groups resist predation, they will be correlated with larger brains.
The interesting relations must be inside the brain -- for instance, are larger neocortex sizes specifically adaptations to group living? Or are they involved with interpreting and acting upon visual signs? Visual signs would include those associated with predators, foods, and other individuals. It's not obvious to me that visual cortex allometry is going to give you a good test of these relations, since adaptation would require interpretation and action upon visual signals, and not merely sensing them.
Anyway, those are some thoughts on the primates vs. snakes paper.
References:
Isbell L. 2006. Snakes as agents of evolutionary change in primate brains. J Hum Evol 51:1-35. DOI link
Cat parasite makes people act like cats
OK, this is just weird. But on the topic of modulating normal brain activity, I have to point out this article in the Times Online (UK).
Dangerrrr: cats could alter your personality
THEY may look like lovable pets but Britain's estimated 9m domestic cats are being blamed by scientists for infecting up to half the population with a parasite that can alter people's personalities.
The startling figures emerge from studies into Toxoplasma gondii, a parasite carried by almost all the country's feline population. They show that half of Britain's human population carry the parasite in their brains, and that infected people may undergo slow but crucial changes in their behaviour.
Infected men, suggests one new study, tend to become more aggressive, scruffy, antisocial and are less attractive. Women, on the other hand, appear to exhibit the "sex kitten" effect, becoming less trustworthy, more desirable, fun-loving and possibly more promiscuous.
Here's another weird thing: the parasite is passed cyclically from cats to rats, and when rats are infected, they tend to lose their natural fear of cats. But the effects on humans are subtle and very interesting:
The study into more subtle changes in human personality is being carried out by Professor Jaroslav Flegr of Charles University in Prague. In one study he subjected more than 300 volunteers to personality profiling while also testing them for toxoplasma.
He found the women infected with toxoplasma spent more money on clothes and were consistently rated as more attractive. "We found they were more easy-going, more warm-hearted, had more friends and cared more about how they looked," he said. "However, they were also less trustworthy and had more relationships with men."
By contrast, the infected men appeared to suffer from the "alley cat" effect: becoming less well groomed undesirable loners who were more willing to fight. They were more likely to be suspicious and jealous. "They tended to dislike following rules," Flegr said.
He also discovered that people infected with toxoplasma had delayed reaction times -- and are at greater risk of being involved in car accidents. "Toxoplasma infection, could represent a serious and highly underestimated economic and public health problem," he said.
In other words, whatever this parasite is doing, it is hooking into the natural human neural processes and modulating them in ways that alter otherwise normal outputs. In some respects, it appears alcohol-like by reducing inhibitions and reaction times. In others, it is highly distinctive. But most interestingly, it is distinctive in ways that are clearly related to the regulation of social interactions. In other words, the parasite exerts the (apparently accidental) effect of driving human mental processes slightly haywire.
One startling fact to emerge from research is the great differences in levels of infection. In France and Germany, for example, about 80%-90% of people are infected -- nearly twice that in Britain or America.
"I am French and I have even wondered if there is an effect on national character," Berdoy said.
Dr Dominique Soldati, a researcher at Imperial College in London, is studying ways of blocking toxoplasma from getting into cells. "Once you are infected you cannot get rid of this parasite and the numbers of them slowly grow over the years," she said. "It's not a nice thought."
There's not a one-liner that even approaches this one...
More on the "suicidal feline attraction"
I covered this story earlier, here's a bit more (from Science Blog):
Researchers have found stronger evidence for a link between a parasite in cat faeces and undercooked meat and an increased risk of schizophrenia.
...
The researchers tested anti-psychotic and mood stabilising medications used for the treatment of schizophrenia on rats infected with T. gondii and found they were as, or more, effective at preventing behaviourial alterations as anti-T. gondii drugs. This led them to believe that T. gondii may have a role in the development of some cases of schizophrenia.
So (here's a reverse) they found that treating the neurological symptoms had the same effect as treating the infection. It reads like another iteration of the H. pylori-gastric ulcer connection, although they are careful to note that it can explain at best a fraction of cases of schizophrenia.
Hopefully the treatment will work on some people. The story says that clinical trials on humans have already begun.
Australopithecine cave match
LiveScience reports on David Carrier's current paper in Evolution:
"The old argument was that [apes] retained short legs to help them climb trees that still were an important part of their habitat," said the study author David Carrier, a biologist at the University of Utah. "My argument is that they retained short legs because short legs helped them fight."
I won't be able to get the paper for awhile. The thesis is that short legs are adaptive to aggressive interactions because short, stout bodies are better for fighting. In addition to the primates mentioned in the article (of which there are only nine), Carrier has in previous papers (Pasi and Carrier 2003, Kemp et al. 2005) studied the relation of limb length and fighting ability among dog breeds.
It looks like Carrier is arguing that the biomechanical advantage of short legs in climbing doesn't really predict arboreality:
As indicators of aggression, Carrier looked at the weight difference between males and females and the male-female difference in length of canine teeth, which are used for biting during battle. Studies have shown greater aggression in primate species in which males tipped the scales relative to females.
Primates with the stoutest figures also ranked high on both aggression measurements. For instance, the gibbons boasted longer legs than other apes and also ranked low on the aggression scale. In contrast, male gorillas, which are more than double the size of females, were stout.
The lengthy legs didn't keep gibbons away from canopies either. "Gibbons are the best acrobats in the animal kingdom. There are no other animals that can move through the canopy the way a gibbon can," Carrier told LiveScience. "And they contrast male gorillas, which hardly ever climb. When they do climb they stay close to the trunk, they spend most of the time on the ground."
I don't know -- australopithecines don't have long canines, and their level of dimorphism has been subject to debate. So the comparison may not work. I'll have to see what the paper says.
References:
Pasi BM, Carrier DR. 2003. Functional trade-offs in the limb muscles of dogs selected for running vs. fighting. J Evol Biol 16:324-332.
Kemp TJ, Bachus KN, Nairn JA, Carrier DR. 2005. Functional trade-offs in the limb bones of dogs selected for running versus fighting. J Exp Biol 208:3475-3482.
Jared Diamond on vengeance cycles
In the New Yorker, Jared Diamond writes a long article with an interesting personal account of revenge cycles in Highland New Guinea:
Hiring, supporting, and rewarding all those allies was a complex logistical operation. Daniel had to feed them during the actual days of combat, to arrange for houses in which they could sleep, and even, as he delicately phrased it, "to provide ladies for the warriors when they were homesick." Daniel estimated that, in the three years that it took him to get his revenge, he had to furnish about three hundred pigs. By custom, the pigs to be slaughtered during that long phase of preparation should be not one's own but, rather, stolen from the enemy clan. Yet Daniel had to be careful to steal only Ombal pigs and not to make the mistake of stealing pigs from other clans; otherwise, he would acquire new enemies.
Many students of anthropology may have seen videos of the large, showy, and ineffectual-seeming "public fights" between groups, and taken away the impression that such small-scale warfare could not be very dangerous. But in the context described by Diamond, this is only the surface of a deeper, more earnest pursuit:
Daniel emphasized the importance of distinguishing between long-range public fights and close-range private ones. He contemptuously described the former as a "small boys' game shoot." As he explained it to me, "Public battles are open not just to experienced fighters but also to new trainees, new allies hired to come and gain confidence, and fun-seekers. In a public battle, the fight-owners have the opportunity to see who really are the best marksmen, with the necessary experience to make quick but correct decisions." Such warriors are selected for the much more dangerous task of private fights, in which hired teams of stealth killers prepare ambushes. "That requires nerve, judgment, and presence of mind, to select the right target, and not to panic and shoot the first man who moves into a shootable position," he said. "Boys and young men are prone to make such mistakes and hence are excluded from the stealth parties."
At the outset of his essay, Diamond suggests that revenge cycles in small-scale societies are equivalents of the dehumanization induced by wars between states. I think this part of the essay is simplistic: he might have profitably explored the differences, the depth of which is suggested by the different psychological reactions that he mentions.
But the end, a personal account from a different culture, is much more evocative.
Spoofing baboons
Nicholas Wade profiles the work of Dorothy Cheney and Robert Seyfarth in this article, "How Baboons Think (Yes, Think)."
Dr. Cheney and Dr. Seyfarth have summed up their new cycle of research in a book titled, after Darwin's comment, "Baboon Metaphysics." Their conclusion, based on many painstaking experiments, is that baboons' minds are specialized for social interaction, for understanding the structure of their complex society and for navigating their way within it.
The shaper of a baboon's mind is natural selection. Those with the best social skills leave the most offspring.
"Monkey society is governed by the same two general rules that governed the behavior of women in so many 19th-century novels," Dr. Cheney and Dr. Seyfarth write. "Stay loyal to your relatives (though perhaps at a distance, if they are an impediment), but also try to ingratiate yourself with the members of high-ranking families."
In other words, Jane Austen would be right at home. I suppose they could have chosen baboons for a "reality" series instead of meerkats, if baboons didn't live so long. It seems like the meerkat deaths generate much of the drama.
The article describes their recent work, playing back sounds at controlled intervals to try to establish when baboons are using social cognition of various flavors.
In some of their playback experiments, Dr. Cheney and Dr. Seyfarth have tested baboons' knowledge of where everyone stands in the hierarchy. In a typical interaction, a dominant baboon gives a threat grunt, and its inferior screams. From their library of recorded baboon sounds, the researchers can fabricate a sequence in which an inferior baboon's threat grunt is followed by a superior's scream.
Baboons pay little attention when a normal interaction is played to them but show surprise when they hear the fabricated sequence implying their social world has been turned upside down.
If they were computers, this would be known as "spoofing." I suppose if they strung together all their wild vocalizations at once, it would be like a Denial of Service attack. Anyway, I think the computer network analogy is helpful -- Cheney and Seyfarth attempt to discover the workings of each node by watching its reactions to various inputs.
The difficulty of field research continues to be the researchers' inability to set up replicated trials of a given sequence of events, and for this reason field primatology has been primarily descriptive. Cheney and Seyfarth mess around with their animals more than most field researchers are willing to do; that provides the opportunity to test certain kinds of hypotheses, but alters the animals' behavior in the process -- precisely why many researchers hesitate to conduct similar playback experiments.
But unlike many other primates, these baboons are not threatened, and their population is healthy. So spoof 'em.
Buller on mental adaptations
I'm reading through David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. It's a back-burner read for me; I pick it up when it's time for the twins to nap. Still, it is hard to put it down in the middle of a chapter.
The book is a critique of evolutionary psychology as practiced now, and an attempt to redirect the field to a better evolutionary grounding. I should mention that throughout Buller refers to "evolutionary psychology as commonly practiced now" as "Evolutionary Psychology" with a big "EP". This is because he has the ambition of establishing an "evolutionary psychology" with a little "ep" by purging all the flaws of the present form. I find this very irritating myself; I would rather he just have come up with another name, just as the "Evolutionary Psychologists" came up with that to replace "sociobiology". So I will try to avoid this confusion by never referring to the field as it "should" be, but only as it exists.
In any event, Buller has an admirable thesis. Unlike other critics, especially Stephen Jay Gould, Buller does not believe that evolutionary psychology has a fatal flaw. Nor does he look for one; he is basically sympathetic with the aims and scope of evolutionary psychology. Instead, Buller thinks that almost every one of the substantive claims of evolutionary psychology are wrong, and that the problems lie in the details of these arguments. So he sets out to deal EP the death of a thousand cuts: outline the major empirical claims of evolutionary psychologists, and explain one-by-one why they are wrong.
Buller on massive modularity
Chapter 4 of David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature is a critique of the concept of massive modularity applied to the human mind. To me, this chapter is weaker than chapter 3, on adaptation, not because the critique is necessarily wrong but because the examples are less compelling.
Buller on mating preferences
Chapter 5 of David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature is mostly about the critique of studies that purport to demonstrate human mate preferences, covering males and females in turn. Buller's critique here is not that the theoretical basis for differences in male and female preferences is weak, or that there is no theoretical reason to suppose the mate preferences asserted by evolutionary psychology (males prefer young fertile females, females prefer high-status males). He does argue against both theoretical points later in the book, however, and here he reiterates his doubt that such preferences might be adaptations and part of a universal developmental program.
But the focus here is to refute the specific evidence that is supposed to demonstrate human mate preferences. Most of the chapter therefore takes the form of a batting practice, as Buller takes pitches from many different studies and clubs them down one by one. It's therefore not the most interesting piece of writing, but it does carry a sort of emotional satisfaction -- sort of like a long game of Whack-a-mole.
Evolutionary psychology responds to Buller
A reader forwarded me a reference to this website, which is a placeholder for present and future critiques to David Buller's book, Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature:
What about David Buller's book, Adapting Minds?
Cultivating a persona of fairness and impartiality, David Buller has written a critique of theory and results from evolutionary psychology. To those unfamiliar with the primary literature, some of his claims may seem plausible. That has not, however, been the reaction of those who know this literature intimately.
Over the next few months, we will be developing on this website a collective response to Buller. It will be collective because we think each scientist should respond to the research that he or she knows best. We will try to provide links to primary sources, so that interested readers can see for themselves what the literature says.
It will take some time. In the meantime, we will post links to the very short replies to Buller to appear in Trends in Cognitive Sciences...
I want to say first that I am a relative outsider to these exchanges. I study human cognitive evolution, and teach it from a broad perspective. As such, I am fairly well aware of the literature in evolutionary psychology, although clearly not as extensively so as its primary participants.
So my biases are my own, and are idiosyncratic compared to many who may care more about the accuracy of particular predictions of evolutionary psychology. As for myself, I find many of the theoretical underpinnings of EP to be unobjectionable, although I think some are very wide of the mark. In my opinion, Buller does good work exposing these and arguing against them for sound evolutionary reasons.
As someone researching the evolution of the mind, I find a large proportion of the specific hypotheses of EP to be useless to me: they make no substantial testable predictions about human fossils, archaeology, or genetic variation. Moreover, although I think it is possible that such cognitive circuits as a "cheater detection module" may have evolved, I see no necessity on the grounds of evolutionary theory or primate comparative biology to suppose that they should have done so.
Buller attacks hypotheses like the "cheater detection module" idea for reasons that I consider to be well-founded. And he does what I consider to be a remarkable job in showing the actual empirical weakness of the data that are supposed to support such hypotheses. Yet, he does not present much positive evidence in support of his own alternative hypotheses. This, I feel, is a drawback of the book. While he does promote alternatives that, by his account, are better explanations of the data, for the most part these alternatives remain to be tested.
In their website, critics of the book present arguments that Buller has misrepresented the evidence for their evolutionary psychology hypotheses. They claim that he has failed to cite studies -- important studies -- that refute his specific views. If this criticism is true, it is indeed a serious flaw.
But a closer look at their website and Buller's book shows that this criticism just isn't true. Here is what the website says about the "cheater detection" issue (hyperlinks available in original):
Here is our response to Buller's attack on the evidence for cheater detection, based on the book and his article, which appeared in Trends in Cognitive Sciences. Because we were limited to 700 words, we could only address the fact that Buller has ignored 15 years worth of evidence showing that his favored alternative hypothesis is false. As time permits, we will expand this response to deal with the other problems with his argument (see Fiddick, Cosmides, & Tooby (2000) on why logic + background assumptions cannot explain our results) and the other ways in which he has misrepresented the empirical literature (e.g., it is not true indicatives need only be "natural" to elicit good violation detection). For a more complete review of the literature on cheater detection and social exchange reasoning--including a review of the evidence that refutes Buller's alternative, deontic, hypothesis-- see Cosmides & Tooby (2005), Neurocognitive adaptations designed for social exchange. Click here for a more complete (and annotated) set (annotated) of publications on this topic.
Perhaps they don't expect people to actually take them up on their "challenge" to read these papers. Perhaps they haven't read Buller's book themselves. The fact is that Buller does discuss Fiddick, Cosmides, and Tooby (2000) -- in fact he devotes well over a page of discussion to it, along with a prominent role in his later argument. If they don't agree with his assessment of that work, it's one thing, but they cannot say he doesn't treat it seriously.
What I find an insult to my intelligence is their apparent assumption that readers of their website cannot use Google to find the relevant literature that they exclude. For example, why don't they themselves refer to this 2002 comment by Sperber and Giotto that argues against the methods and conclusions of Fiddick, Cosmides, and Tooby (2000)? Abstract:
Sperber, Cara, and Girotto (Cognition 52 (1995) 3) argued that, in Wason's selection task, relevance-guided comprehension processes tend to determine participants' performance and pre-empt the use of other inferential capacities. Because of this, the value of the selection task as a tool for studying human inference has been grossly overestimated. Fiddick, Cosmides, and Tooby (Cognition 77 (2000) 1) argued against Sperber et al. that specialized inferential mechanisms, in particular the "social contract algorithm" hypothesized by Cosmides (Cognition 31 (1989) 187), pre-empt more general comprehension abilities, making the selection task a useful tool after all. We rebut this argument. We argue and illustrate with two new experiments, that Fiddick et al. mix the true Wason selection task with a trivially simple categorization task superficially similar to the Wason task, yielding methodologically flawed evidence. We conclude that the extensive use of various kinds of selection tasks in the psychology of reasoning has been quite counter-productive and should be discontinued.
Why is there no citation to that work in Cosmides and Tooby's (2005) "more complete review"? Why does the "more complete review" fail to discuss the weaknesses of their research with Fiddick? Why does it persist in the fallacy that "social exchange" and "social contracts" are the same thing? Why does it exclude the later argument of Fodor (2000), which ends thusly:
What seems clear, in any case, is that Cosmides and Tooby's original assumption that requirement-hypotheticals and regularity-hypotheticals have the same logical form was unsound. I'm grateful to Beaman for thus demonstrating empirically what I had urged on a priori grounds.
Now all of these arguments could be wrong. Perhaps they really pose no problem to Cosmides and Tooby's preferred interpretation.
But it seems to me that the failure to acknowledge them is not a good sign. Not a single critical article is listed on the "complete (and annotated) set (annotated) of publications". Clearly anyone going to that website is going to get a far more one-sided view of the issue than Buller's book has presented.
They have every right to present whatever they want, but it is especially galling that in a response to a book that does include their arguments, they claim "Buller has ignored 15 years worth of evidence", when they can't appear to be bothered to cite, much less discuss other papers critical of their views.
I'm no shill for Buller. I don't know him, have never met him, and my only extensive experience with his arguments is from reading his book. I have expressed some of my own reservations about his arguments in my reviews, which nevertheless have been broadly positive. As with the weblog in general, these are my mostly unvarnished reactions and notes; if I didn't have a positive opinion, I certainly wouldn't write one.
Whether he is right about every specific hypothesis he critiques remains to be seen, and hopefully tested. But with the exchange developing as it is, I wouldn't lay much money on him being wrong.
Buller on Buller
On the subject of objections to Buller's book, I should point out that Buller himself has a website where he has additional work and some responses to critics (particularly this reply to the short comments in TiCS).
Also on the subject, does anybody else think this debate is looking very much like the crocodile vs. python deathmatch from last week?
Like father, like son
If you've ever noticed that kids have the same facial expressions as their parents, you're not alone. The usual explanation for this similarity is learning -- kids watch their parents' facial expressions and then take them on themselves. This seems like a natural hypothesis considering another well-worn observation: that couples tend to resemble each other more and more over time. What more rational basis for this resemblance than subconsciously adopting each others' facial expressions?
But so far, we're really in "old wives' tale" territory. There is another hypothesis for similarity between parents and kids -- that their genes make them look similar. Peleg and colleagues (2006) have examined facial expressions in families to test whether genes underlie the variation to an observable extent.
The really interesting part is that they test a sample of blind subjects for similarities in facial expressions with their relatives.
Here's the abstract:
Although facial expressions of emotion are universal, individual differences create a facial expression "signature" for each person; but, is there a unique family facial expression signature? Only a few family studies on the heredity of facial expressions have been performed, none of which compared the gestalt of movements in various emotional states; they compared only a few movements in one or two emotional states. No studies, to our knowledge, have compared movements of congenitally blind subjects with their relatives to our knowledge. Using two types of analyses, we show a correlation between movements of congenitally blind subjects with those of their relatives in think-concentrate, sadness, anger, disgust, joy, and surprise and provide evidence for a unique family facial expression signature. In the analysis "in-out family test," a particular movement was compared each time across subjects. Results show that the frequency of occurrence of a movement of a congenitally blind subject in his family is significantly higher than that outside of his family in think-concentrate, sadness, and anger. In the analysis "the classification test," in which congenitally blind subjects were classified to their families according to the gestalt of movements, results show 80% correct classification over the entire interview and 75% in anger. Analysis of the movements' frequencies in anger revealed a correlation between the movements' frequencies of congenitally blind individuals and those of their relatives. This study anticipates discovering genes that influence facial expressions, understanding their evolutionary significance, and elucidating repair mechanisms for syndromes lacking facial expression, such as autism.
Turns out that Darwin had the idea first:
About 130 years ago, Darwin mentioned facial expressions in blind-from-birth individuals in the context of heritability: "The inheritance of most of our expressive actions explains the fact that those born blind display them, as I hear from the Rev. R. H. Blair, equally well with those gifted with eyesight" (Peleg et al. 2006:15922).
Still, the study is incomplete -- it has a small sample of subjects, and doesn't have the data to try to estimate the heritability of these expressions. Indeed, as "gestalts," the expressions themselves are statistically difficult to work with.
And speaking of facial expressions -- tonight's "Dancing with the Stars" show featured a body language expert examining how each of the competitors responds subconsciously to being judged. Mario Lopez takes a submissive posture when he is about to hear what the judges say, while Joey Lawrence licks his lips compulsively out of nervousness. They'd better stay out of poker games!
References:
Peleg G, Katzir G, Peleg O, Kamara M, Brodsky L, Hel-Or H, Keren D, Nevo E. 2006. Hereditary family signature of facial expression. Proc Nat Acad Sci USA 103:15921-15926. DOI link
Monkey signal modulation
A current paper by Flack and Frans de Waal (2007) shows one of the main reasons why monkeys are a bit more sophisticated than fish in their signaling about dominance. They studied the way that pigtailed macaques (Macaca nemestrina) use a submission signal in the context of a fight and also in other contexts.
The submission signal is a "silent bared-teeth display". This display is given by individuals who are confronted by threat or aggression from other individuals; it reduces conflict by signalling an unwillingness to fight.
The bottom line of the paper is that these macaques sometimes use the submission signal in entirely peaceful contexts where no threat or aggressive behavior has occurred. Individuals who use the submission signal with each other are significantly more likely to groom each other, and groom more often than nonsignalers. So it appears that the silent bared-teeth display is a signal the meaning of which depends on social context -- in the context of aggression it signals submission, while outside the context of aggression it signals subordination.