Mad alligators and, insert cliché here
On the topic of how to measure intelligence in different species, I found this passage on pp. 256-257 of Georg Streidter's textbook:
Over the last 50 years or so, it has become apparent that some nonmammals perform just as well as mammals in various learning and "intelligence" tests, as long as the tests are designed with the animal's "special needs" in mind. Davidson (1966), for example, showed that alligators fail to learn a simple discrimination task if the reward is food, but readily master the same task, in the same apparatus, if they are offered the opportunity to escape from excessive heat. Such a finding might have surprised Tinklepaugh or Edinger, but it makes perfect sense once you realize that alligators (as ectothermic creatures with low metabolic rates) can go without food for long periods of time but must frequently move out of the sun to prevent heatstroke. In other words, comparative psychologists have realized that it is blatantly unfair to run reptiles or other nonmammals through intelligence tests that were designed by mammals for mammals (Streidter 2005:256-257).
This is near the beginning of a chapter on mammalian brain evolution, the introduction of which ends: "After all, the subject of the book is the evolution of brains, not intelligence" (258). The focus on the functional and the adaptive is refreshing -- since the evolutionary utility of the brain is for solving adaptive problems.
Nevertheless, he later links expanding brain size on the mammal lineage with metabolic rate -- which may be the most straightforward of possible connections, since the sensory evolution of early mammals involved both complex gains (e.g., olfactory) and losses (e.g. chromatic vision) of function.
I'll probably be quoting more as I get into this.
References:
Davidson RS. 1966. Operate stimulus control applied to maze behavior: heat escape conditioning and discrimination reversal in Alligator mississippiensis. J Exp Anal Behav 9:671-676.
Streidter GF. 2005. Principles of Brain Evolution. Sinauer, Sunderland MA.
Red and black, antennae waving
I am more or less fascinated by these ants who count their steps to find their way home. It's just that we use such a massive amount of cognitive overhead for any kind of counting -- with our numeric symbol sets, and language acquisition, and so on -- and here these ants are counting perfectly well (and more accurately than us most of the time, I presume) by just using some kind of ticker.
That, and the whole concept of putting tiny stilts on the ants to screw up their stride lengths.
References:
Wittlinger M, Wehner R, Wolf H. 2006. The ant odometer: stepping on stilts and stumps. Science 312:1965-1967. Abstract
Waggle information
A nice post on bee dancing and the bee sensory system at Neurophilosophy. From an information perspective, here we have a good example of adapting a nervous and sensory system to maximize information transfer through a given channel. In this case, the channel is defined by the frequency of bee wingbeats, particularly during the waggle dance. The critical sensory apparatus of the antennae turns out to be a simple machine for picking up these signals.
It was found that the antennae of mature worker bees are most sensitive to sounds with a frequency of between 250-300 Hz, and that the frequency and timing of the flagellar vibrations are accurately translated into the neural responses of the sensory cells in the Johnson's organ. The worker bees' hearing is therefore perfectly tuned to detect the movements of other bees, and the auditory system is ideal for listening in on the sounds made by other workers performing a dance no more than several millimetres away.
The extra twist is that worker bees differentiate their activities by age, and only older bees can hear the waggle dance at maximal efficiency. Younger bees who don't forage for food also don't have the sensitivity in the right range of frequencies.
It's a simple model with ontogenetic change in information receptivity.
References
Tsujiuchi, S., et al (2007). Dynamic range compression in the honey bee auditory system toward waggle dance sounds. PLoS One 2: e234. doi:10.1371/journal.pone.0000234.
Elephants on the attack
Charles Siebert of the Times had a story this weekend about aggression by young bull elephants. It has a name now, HEC (human-elephant conflict). And it has taken a chilling turn:
Still, it is not only the increasing number of these incidents that is causing alarm but also the singular perversity -- for want of a less anthropocentric term -- of recent elephant aggression. Since the early 1990's, for example, young male elephants in Pilanesberg National Park and the Hluhluwe-Umfolozi Game Reserve in South Africa have been raping and killing rhinoceroses; this abnormal behavior, according to a 2001 study in the journal Pachyderm, has been reported in "a number of reserves" in the region. In July of last year, officials in Pilanesberg shot three young male elephants who were responsible for the killings of 63 rhinos, as well as attacks on people in safari vehicles. In Addo Elephant National Park, also in South Africa, up to 90 percent of male elephant deaths are now attributable to other male elephants, compared with a rate of 6 percent in more stable elephant communities.
Personally, I think that 6 percent is impressively high -- that is a huge toll in a species with such long life histories.
In human deaths:
In the Indian state Jharkhand near the western border of Bangladesh, 300 people were killed by elephants between 2000 and 2004. In the past 12 years, elephants have killed 605 people in Assam, a state in northeastern India, 239 of them since 2001; 265 elephants have died in that same period, the majority of them as a result of retaliation by angry villagers, who have used everything from poison-tipped arrows to laced food to exact their revenge. In Africa, reports of human-elephant conflicts appear almost daily, from Zambia to Tanzania, from Uganda to Sierra Leone, where 300 villagers evacuated their homes last year because of unprovoked elephant attacks.
It's a long story that goes into the study of elephant social behavior and relates psychological trauma in elephants to the mechanisms underlying it in humans. There's also a fascinating account of the time that a man-killing circus elephant was hanged (yes, hanged) for the crime.
UPDATE (10/10/2006): From Reuters:
Indians flee as elephants search for dead friend
RANCHI, India - Thousands of people in eastern India have fled their homes in fear as elephants crash through villages looking for one of their herd, which fell into a ditch and drowned over the weekend, officials said Tuesday.
Residents of Banta in Jharkhand state gave the 17-year-old female elephant a quiet burial three days ago, but 14 marauding elephants have been raiding the village ever since.
I find it eerily creepy the way that the journalists in these stories have chosen to anthropomorphize the elephants. Now, to be sure the elephant reactions may well involve a very similar psychological process to humans in similar situations (loss of companions, crowding in unfamiliar habitat). But here they are described in almost exactly the same terms that one would describe humans in the same situation (fighting off encroaching development, dealing with losses at the hands of other people):
With forest cover dwindling in eastern India, elephants and other animals regularly leave their forest homes in search of food, triggering conflict with locals.
The description of the rhino-raping is one of the few elements that really stand out as inhuman, and that's why it is so striking. But these stories have a very consistent theme, and it is a theme taken straight from Edgar Rice Burroughs. Somebody should teach these journalists better.
Elephants don't climb hills
At least, not willingly, says this article, citing a short study by Jake Wall et al. in Current Biology.
But the researchers calculate that the energy required to climb a hill could be a main factor. Climbing uphill for 100 yards would require a half-hour of foraging to replace the energy used.
References:
Wall J, Douglas-Hamilton I, Vollrath F. 2006. Elephants avoid costly mountaineering. Curr Biol 16:R527-R529. DOI link
Girlie fly necroMANIA!
You have to have a pretty weird science story to get traction this week, and Reuters serves one up:
Gene swap makes boy flies fight like girls
The researchers swapped the male and female versions of the gene in fruit flies and observed the consequences. Males with the feminine gene used female fighting tactics, while the females with the masculine gene fought like the boys.
The story doesn't explain why there are male and female "versions" of the gene, but the actual research by Vrontou et al. sheds some light:
We speculated that the fruitless (fru) gene might be involved in specifying these sex differences in aggression and dominance. This inference was based on fru's critical role in another sex-specific social behavior, male courtship, as well as on an earlier report of anomalous interactions in fru mutant males that were subsequently found to be characteristic of normal female fights. The fru gene produces multiple transcripts, all of which are thought to encode zinc-finger transcription factors. Transcripts from the distal P1 promoter are sex-specifically spliced, resulting in male-specific mRNAs that encode full-length Fru proteins (FruM) and female-specific mRNAs that are evidently not translated. We previously generated alleles of fru that are constitutively spliced in either the male (fruM) or female (fruF) mode, irrespective of the sex of the fly. An additional control allele (fruC) is subject to normal sex-specific splicing.
Anyway, doing the switch-up between the male expressed version and the female nontranslated version causes a reversal of gender roles in these fights. Actually, the research paper has a much more flavorful description of these than the Reuters article:
Under the appropriate conditions, pairs of male or female flies will fight each other, displaying a distinctive set of aggressive behaviors (Supplementary Videos 1 and 2 online). Some of these behavioral components are common to both male and female fights, such as low-intensity 'fencing.' Other components, particularly those of higher intensity, are much more frequent in one sex than the other. For example, 'lunging' and 'boxing' are mostly seen in male fights, whereas 'shoving' and 'head-butting' are characteristic of female fights.
Oh yes, you read that correctly. The supplementary info includes videos.
And how can you not watch with a set-up like this?
They set up the insect world's equivalent to a steel-cage match - a chamber with glass walls and a lid with air holes, a dish of fly food and a mate - and sent in the combatants. But when they used a live female fly as a lure for the males, she often would just fly off.
"My student discovered when he transferred the female to the dish and accidentally crushed her head that the males didn't care whether she had a head or not. That's a true story of what led us to cutting the heads of the females off in subsequent studies," Kravitz said. "They'll court the dead, headless female fly, and try to copulate with her sometimes."
I must admit, it is more interesting than I thought fruit fly fights would end up being. They actually do "box" each other!
I can't tell what they're fighting on, though -- maybe it's one of those new candles from Glah-day...
References:
Vrontou E, Nilsen SP, Demir E, Kravitz EA, Dickson BJ. 2006. fruitless regulates aggression and dominance in Drosophila. Nature Neurosci Early online DOI link
Meerkat teaching
It's all meerkats all over the place today. Here's an AP article by Randolph Schmid:
Researchers from the University of Cambridge in England observed meerkats gradually introducing cubs to prey, showing them how to handle captured insects and even removing the stingers from scorpions before giving them to youngsters.
"Although there are anecdotal reports of teaching in species from chimpanzees to killer whales, until this year solid evidence was really lacking," said Alex Thornton, co-author of the report appearing in Friday's issue of the journal Science.
Here's the article by Thornton and McAuliffe. Much hangs on the definition of "teaching", in this paper that definition really comes at the end:
The results of this study provide strong evidence that the provisioning behavior of meerkat helpers constitutes a form of "opportunity teaching," in which teachers provide pupils with opportunities to practice skills, thus facilitating learning (3, 7). Helpers modified their behavior in the presence of pups, gradually introducing them to live prey, monitoring their handling behavior, nudging prey, and retrieving and further modifying prey if necessary. Dangerous items were more likely to be killed or disabled than other mobile prey. Helpers gained no direct benefits from their provisioning behavior and incurred costs through giving pups prey that was difficult to handle and might escape. Finally, there was strong evidence that helper provisioning behavior plays an important role in promoting the development of pup handling skills.
It is often assumed that teaching requires awareness of the ignorance of pupils and a deliberate attempt to correct that ignorance (5, 6, 20), but viewed from a functional perspective (3), teaching can be based on simple mechanisms without the need for intentionality and the attribution of mental states. By differentially responding to the calls of pups of different ages, helpers may accelerate pups' learning of handling skills without the need for complex cognitive processes. Additional post-provisioning behavior, such as nudging and retrieving prey, may then further enhance skill acquisition.
In the last paragraph, Thornton and McAuliffe place the meerkats in a broader context:
Evidence from ants (10) and meerkats suggests that teaching, as defined by Caro and Hauser (3), may have evolved independently in many unrelated taxa. Where individuals must acquire critical skills or information but individual learning is costly or opportunities to practice are lacking, selection may favor mechanisms whereby experienced individuals actively facilitate learning by naïve conspecifics. The paucity of evidence for teaching is likely to reflect difficulties in producing unequivocal support for strict criteria rather than an absence of teaching per se. As evidence for teaching in nonhuman animals emerges, research will be in a position to look in more detail at the conditions under which teaching is likely to evolve and to relate forms of teaching found in humans and other animals in a broad framework.
Personally, I think that "theory of mind", insofar as it exists, must consist precisely of the sorts of knowledge that allow teaching to happen. In other words, you have to be able to assess whether another individual "gets" the information you are trying to send with your efforts. And from that perspective, the only distinction between teaching and communication is the kind of effort that goes into it -- which in the case of teaching is generally either progressive or repetitive. Those kinds of cases are the ones that fulfill "strict criteria", at least; a simple communication may convey just as much information or more (to a suitably primed individual), but has less oomph to it in examining the behavior of the teacher.
But then, there are the ants. In case you missed that paper, here's the abstract:
The ant Temnothorax albipennis uses a technique known as tandem running to lead another ant from the nest to food--with signals between the two ants controlling both the speed and course of the run. Here we analyse the results of this communication and show that tandem running is an example of teaching, to our knowledge the first in a non-human animal, that involves bidirectional feedback between teacher and pupil. This behaviour indicates that it could be the value of information, rather than the constraint of brain size, that has influenced the evolution of teaching.
The key element in that definition of teaching is the bidirectional feedback. And bidirectional feedback does at least involve the concept of being able to read the signs that a learner is responding appropriately. For the ants, there is little information being exchanged to maintain the system. In a real sense, the teacher ant doesn't have to have very much information about the learner to assess that the learner is responding appropriately. We could imagine how a robot might be built to "teach" this kind of task. It's essentially what Lassie does whenever Timmy gets stuck in trouble somewhere.
But by the same token, the meerkat teachers may not need much information to judge their learners' responses. They just repeatedly present food to the learners; and the learners' eating, playing or whatever give the feedback. Now, there is something more complicated here -- the learner is learning signs. The desired outcome is that certain animals will be recognized by the learners as food, which requires the involvement of specialized visual, olfactory, and other cognitive subsystems. But the teachers aren't creating this entire system; they are only presenting a consistent set of associations. Nor do the teachers have to judge the workings of every stage of cognition -- "theory of mind" need not go anywhere near that far. They just have to rachet the teaching when they perceive appropriate responses by the learners.
So I think this is hardly less robotic than the ants. The additional complexity is not in the communication between teacher and learner, but in the perceptual systems necessary to carry out the communication.
And I think that's the point -- the feedback communication that enables the evolution of teaching (at least, this kind of teaching) is pretty simple (that is, it doesn't require a large channel). The story is that mammal brains (and primate brains in particular) do a very good job of abstracting this narrow channel of communciation out of the very broad sensory inputs available (vastly moreso than the chemical and tactile system used by ants). And that they are then so successful at using the limited communications to model other individuals.
References:
Thornton A, McAuliffe K. 2006. Teaching in wild meerkats. Science 313:227-229. DOI link
Franks NR, Richardson T. 2006. Teaching in tandem-running ants. Nature 439:153. PubMed
FoxP2 knockout mice
Yesterday's post on mice mating songs left with a final question: Do FoxP2 knockout mice sing?
Thanks to a kind reader, I have a probable answer: no.
Although nobody has looked specifically at ultrasonic vocalizations in response to mating (since they didn't know about the singing before), they have studied ultrasonic vocalizations in pups when they are separated from their mothers. This paper by Weiguo Shu and colleagues (2005) studied such vocalizations in both heterozygous and homozygous knockouts.
Because FOXP2 has been directly implicated in speech and articulation, we examined the incidence of ultrasonic vocalizations in pups removed from their mothers. Ultrasonic calls are important for motherÐinfant social interaction (16) and represent important markers for neurobehavioral development (17). At postnatal day 6, the incidence of vocalization over time was dramatically reduced in both heterozygous and knockout animals as measured by automated vocalization monitoring (Fig. 4a). Repeated measures analysis demonstrated differences in mean number of vocalizations (P < 0.0005 for wild-type versus knockout and P = 0.008 for wild-type versus heterozygotes).
Based on these results, we performed a spectrographic analysis of an independent group of animals at postnatal day 10 (e.g., Fig. 4b). There was a profound decrease in the number of ultrasonic vocalizations in heterozygous and homozygous knockout animals (Fig. 4c). The duration, peak frequency, and bandwidth of these vocalizations in the heterozygous animals were indistinguishable from wild-type animals (data not shown). In the course of these analyses, we also examined broad-spectrum clicks made by the mice. These clicks are of unknown function (18), and the information content of them has not been studied. Heterozygous and homozygous knockout animals were able to produce clicks, but the homozygous knockout animals produced clicks at a reduced incidence (Fig. 4d). The duration, peak frequency, and bandwidth of these vocalizations in the heterozygous and homozygous knockout animals were indistinguishable from wild-type animals (emphasis added).
Homozygote knockouts died prematurely, by 21 days after birth. Heterozygotes lived, but exhibited developmental delays.
The paper included histological study of the brains of the knockout mice, with this interesting finding:
No overt abnormalities were detected in the histologic appearance of the cerebral hemispheres and the subcortical structures, including the midbrain and pons. However, the knockout mice demonstrated the presence of a 3- to 4-cell thick external granular layer (EGL) at postnatal days 15Ð17, well after the normal resolution of the EGL (Fig. 3 aÐf). The heterozygous animals retained a one-cell-thick EGL at this age, whereas the wild-type mice were free of this early developmental feature. By adulthood, the EGL was absent in heterozygous animals (data not shown).
...
Granule cell progenitors in the EGL migrate to their final position in the granule cell layer along the radial fibers of the Bergmann glia (14). To determine whether the persistence of an EGL in the knockout animal might be at least, in part, explained by a failure of radial glial development, we stained radial glial fibers in cerebellar sections from postnatal day 17 animals with GFAP immunostaining (Fig. 3 jÐl). Radial glial fibers were visible in all genotypes. However, in contrast to the regularly aligned radial glial fibers in the wild-type animals, fibers in the heterozygous animals were in some areas thinner and less well aligned. In the knockout animals, there were often gaps in the radial glial network as well as areas where fibers appeared to be clumped into aggregates.
It's interesting to me that neural cell migration appears to be (at least one) important effect of the gene. This is the developmental step that forms the circuits in the brain.
References:
Shu W, Cho JY, Jiang Y, Zhang M, Weisz D, Elder GA, Schmeidler J, De Gasperi R, Sosa MA, Rabidou D, Santucci AC, Perl D, Morrisey E, Buxbaum JD. 2005. Altered ultrasonic vocalization in mice with a disruption in the Foxp2 gene. Proc Natl Acad Sci U S A 102:9643-9648. Full text (free)
Who's the leader of the club that's made for you and me?
According to this PLoS Biology paper by Timothy Holy and Zhongsheng Guo, mice can sing.
Previously it was shown that male mice, when they encounter female mice or their pheromones, emit ultrasonic vocalizations with frequencies ranging over 30Ð110 kHz. Here, we show that these vocalizations have the characteristics of song, consisting of several different syllable types, whose temporal sequencing includes the utterance of repeated phrases. Individual males produce songs with characteristic syllabic and temporal structure. This study provides a quantitative initial description of male mouse songs, and opens the possibility of studying song production and perception in an established genetic model organism (Holy and Guo 2005:e386).
The songs are ultrasonic, but share characteristics of organization with certain bird songs:
The richness and complexity of mouse song appear to approach that of many songbirds. For example, in the zebra finch, a widely used model organism for studying song production, individuals have a number (3Ð7) of syllable types [25,33] similar to the number of common types we find in mice (Table 1). There are other species, for example, canaries, whose vocal repertoire would appear to exceed that of mice [34]. Both mice (see Figure 6) and birds [25,33] exhibit regular temporal structure in their songs, including the production of repeated themes with sharp transitions between syllable types. However, mice also exhibit more gradual changes in syllable structure (see Figure 1). Overall, the tendency to repeat a syllable, with sharp transitions between types, appears to be stronger in some birds [34] and whales [3] than in mice. However, in birds these sharp transitions are a feature of the adult "crystallized" song; juvenile or isolation-reared birds are more experimental and less predictable in terms of the temporal structure of their song [33,35]. Indeed, our pitch-shifted recordings of mouse song sound similar to the early "plastic" song of species such as swamp sparrows (Audio S5). For this reason, any comparison between birds and mice should consider the development of mouse song over the lifetime of the animal. Such a study has been undertaken for properties like mean pitch and cadence over the first 2 wk of life [12], but is lacking for the more complex features that compose song (ibid.).
And I find this suggestion really interesting:
Because mouse songs are ultrasonic and therefore inaudible to human ears, it is worth noting that laboratory domestication has probably not acted to preserve the full richness of mouse song through generations inbreeding. One study documented considerable variability in the amount of vocalization by different laboratory strains [36]. In contrast, domesticated bird populations have been subject to song selection, and indeed sub-strains such as the Waterschlager canary have been bred for particular vocal qualities. It therefore seems possible that wild mice might exhibit considerably greater diversity and/or more complex structure in their songs. Future comparisons between the songs of mice and birds may benefit from using wild mice (ibid.).
Mouse song is a previously unobserved aspect of biology suddenly discovered after decades of selection that ignored it completely. Different laboratory strains (that differ both because of drift and because they were selected for different things) potentially have different song capabilities. I wonder if all the good singers are related? Or if mice bred for delayed mating still sing?
Next probable step: do FoxP2 knockout mice sing?
UPDATE (11/2/05): I love it when answers fall from the e-mail tree! See second post for the answer to the final question.
References:
Holy TE, Guo Z. 2005. Ultrasonic songs of male mice. PLoS Biol 3:e386. Full text (free)
Reciprocity and rats
Rutte and Taborsky report in PLoS Biology that their rats know how to be nice to others:
The evolution of cooperation is based on four general mechanisms: mutualism, where an action benefits all partners directly; kin selection, where related individuals are supported; "green beard" altruism that is based on a genetic correlation between altruism genes and respective markers; and reciprocal altruism, where helpful acts are contingent upon the likelihood of getting help in return. The latter mechanism is intriguing because it is prone to exploitation. In theory, reciprocal altruism may evolve by direct, indirect, "strong," and generalized reciprocity. Apart from direct reciprocity, where individuals base their behavior towards a partner on that partner's previous behavior towards themselves, and which works under only highly restrictive conditions, no other mechanism for reciprocity has been demonstrated among conspecifics in nonhuman animals. Here, we tested the propensity of wild-type Norway rats to help unknown conspecifics in response to help received from other unknown partners in an instrumental cooperative task. Anonymous receipt of help increased their propensity to help by more than 20%, revealing that nonhuman animals may indeed show generalized reciprocity. This mechanism causes altruistic behavior by previous social experience irrespective of partner identity. Generalized reciprocity is hence much simpler and therefore more likely to be important in nature than other reciprocity mechanisms.
In the discussion of the paper, the authors describe the results of other experiments that suggest rats are even more cooperative when repeated interactions occur:
In a follow-up study we tested whether the propensity to cooperate would be increased further when Norway rats interacted with a known partner who had helped them before [32]. As expected, this direct reciprocity caused even higher levels of cooperation than generalized reciprocity, i.e., a rat was 50.7% more likely to help a conspecific who had helped her before than an unknown rat after experiencing cooperation with anonymous partners. This is compatible with a "hierarchical information hypothesis" assuming that specific information about the helping propensity of a partner is used if available, but if not, anonymous social experience is used when deciding whether to cooperate or not [32], i.e., cooperation may ensue also when specific information is limited or costly to be obtained. A similar mechanism might operate in humans [29]. Theoretical models showed that the existence of direct reciprocity in a population will induce the evolution of generalized reciprocity [22], entailing much higher levels of cooperation overall.
Well, lab rats aren't necessarily the same as wild rats, so I suppose it's possible that these rats are doing unusual things compared to their natural habitat. But I'm not really surprised that rats would be capable of either general or direct reciprocity. The game theoretic basis of reciprocity is very simple, and can easily be implemented in a short algorithm. The hard part is when you try to be choosy about it -- determining exactly the right social situations in which a bias toward reciprocity pays off. Evolving the bias in a social species might be very easy. Finding that rats exhibit the behavior under some circumstances tends to confirm that this class of altruism may evolve readily, in even a modestly social species.
I take it as a suggestion that this probably isn't the main reason why humans evolved large brains...
References:
Rutte C, Taborsky M. 2007. Generalized reciprocity in rats. PLoS Biol 5:e196. doi:10.1371/journal.pbio.0050196
Rat races
Read Nick Wade's article about Siberian rat breeding experiments. Two strains of rat: one tame and one aggressive. Now they're screening their genomes to see what's up.
"The ferocious rats cannot be handled," Mr. Albert said. "They will not tolerate it. They go totally crazy if you try to pick them up."
When the aggressive rats have to be moved, Mr. Albert places two cages side by side with the doors open and lets the rats change cages by themselves. He is taking care that they do not escape to the sewers of Leipzig, he said.
Well, those might be some nasty rats, but odds are they wouldn't do too well in a natural sewer. Their Siberian rat cages protect them just as much as their tame relatives; their alleles probably are already present in the wild population, and the pattern of selection on them almost certainly wouldn't change just because of their release.
(I know what you're thinking. The rats from NiMH were entirely different! They had some kind of special pharmaceutical alteration.)
The article covers Belyaev's experiments, which are best known for the tame foxes:
The experiment did not become widely known outside Russia until 1999, when Dr. Trut published an article in American Scientist. She reported that after 40 years of the experiment, and the breeding of 45,000 foxes, a group of animals had emerged that were as tame and as eager to please as a dog.
As Belyaev had predicted, other changes appeared along with the tameness, even though they had not been selected for. The tame silver foxes had begun to show white patches on their fur, floppy ears, rolled tails and smaller skulls.
Sure, the founding of the breeding population would have gotten a few rare alleles by chance, but we're really talking about the selection of alleles that are mostly already fairly common in wild foxes (common enough to get into a small sample of them, anyway). So this breeding experiment has concentrated a few alleles that are generally present into a single group where they are always coexpressed.
Anyway, nobody ever seems to talk about the other colony of "vicious" foxes. The article covers a few surprising correlates of tameness, like the ability to follow gaze. But what are the surprising correlates of aggressiveness? Are these foxes and rats sociopaths?
The root question is whether humans domesticated themselves, and therefore have some of the same genetic changes as these domesticated rats and foxes. But then, the rats and foxes haven't so much undergone genetic changes as simple enrichment of alleles that are already common. Which means that they may have unusual phenotypes as a result of these alleles being coincident at high frequencies, but those alleles already are doing something in normal, wild (and mostly solitary) animals. This doesn't mean that the tame phenotype should already exist -- even if all these alleles are independently common, if there are enough of them they may never all be present in any single wild individual.
So the interesting question is why these alleles that permit domestication in combination should already be common. Do they all contribute to variant behavioral strategies -- such as a proper balance of fear, aggression, tolerance, and sociality? Are they all in selective balance? They aren't all present because they make animals tame, at least, not if tame animals are naturally rare. But each has some advantage on the wild genetic background, or they wouldn't persist as common functional variants.
And if these genes did change in identifiable ways during human evolution, well then, what started the process? It is easy to imagine sociality evolving in parallel in humans and domesticated animals -- at least in certain respects -- but widespread changes in systems that are often found in selective balances would be sort of surprising. With domesticated animals there is a huge fitness cost to aggression. Is that really true of people?
It's a great topic, and a great story. Considering how much money there is in beef, it seems like it would be a small investment to raise 40,000 bison, or pronghorn, or eland, or any number of other wild animals to select for tameness. Maybe Ted Turner could do it.
The cockroach poll
It's minor election day here in Wisconsin, and I see this story (discovery.com) about how cockroaches "make group decisions":
Cockroaches govern themselves in a very simple democracy where each insect has equal standing and group consultations precede decisions that affect the entire group, indicates a new study.
The research determined that cockroach decision-making follows a predictable pattern that could explain group dynamics of other insects and animals, such as ants, spiders, fish and even cows.
Now, what kind of decision are we talking about?
Halloy tested cockroach group behavior by placing the insects in a dish that contained three shelters. The test was to see how the cockroaches would divide themselves into the shelters.
After much "consultation," through antenna probing, touching and more, the cockroaches divided themselves up perfectly within the shelters. For example, if 50 insects were placed in a dish with three shelters, each with a capacity for 40 bugs, 25 roaches huddled together in the first shelter, 25 gathered in the second shelter, and the third was left vacant.
When the researchers altered this setup so that it had three shelters with a capacity for more than 50 insects, all of the cockroaches moved into the first "house."
This isn't really a roach democracy. But it is sort of analogous to much simpler human decisions, like the snap judgment about which bathroom stall to use, for example. It's based on observing what someone else is going to do, and making a quick assessment of the best option, and often leads to that quick hesitation. It's a bit more complex than working out who goes at a four-way stop, since there is the issue of optimizing the individual outcome.
I'm beginning to wonder if there's anything that humans do culturally that some insect didn't also evolve to do. Now, that's not to say that any insect has the full set of things, just that they seem to have explored a wide swath of the possibilities of social interactions, and have come to many of the same solutions that people do.
And what's the deal with the roach "house"? Shouldn't that be "hotel"?
How to move like a vertebrate
Neurophilosophy has really come to life in the last few weeks. A post earlier this week described the neural circuitry that controls swimming in zebrafish, from work published in Nature. Today's post takes the evolution of motion up to tetrapods, with a description of a robotic salamander and what it tells scientists about motor control systems.
And this post about rat metacognition covers the Current Biology paper by Foote and Crystal so I don't have to:
Jonathan Crystal and Allison Foote, of the University of Georgiaâs Department of Psychology, taught rats to associate two different auditory stimuli with different levers. A short burst of static, lasting around 2 seconds, was associated with one lever, and a longer burst, lasting up to 8 seconds, with another. In the second phase of the trials, the sounds were played back to the rats. When the lever associated with each sound was correctly pressed, the rats were given a large reward - 6 food pellets. But if the wrong lever was pressed, they received no reward. The rats were also given the option to decline taking the test - they learnt that they could retrieve a smaller reward - 3 food pellets - without making a decision about which lever to press, by poking their snout through an aperture in a food trough.
During the test phase, the rats were presented with the short and long bursts of static, as well as with bursts of intermediate length, and their responses were recorded. When the length of the sound burst was unambiguous (i.e. either short or long) they ignored the food trough and pressed the lever associated with the sound, so that they received the large reward. But when sounds of an intermediate length (approximately 3 seconds) were played, the rats frequently declined to take the test, and chose instead to retrieve food pellets from the food trough, suggesting that the rats knew that they did not know how to respond in the duration discrimination test.
The paper concludes that the rats have a concept of what they know they know -- that is, a metacognitive concept. My students this week told me that rats are smart; I suppose it's true enough.
References:
Foote, AL, Crystal, JD. 2007. Metacognition in the rat. Curr. Biol. doi:10.1016/j.cub.2007.01.061
Rodent tool use
It's not just any rodents, but the "highly social, intelligent" degus. And they don't use tools in their natural habitats, but were taught specially by researchers. But it's still pretty interesting:
After two months of practice, researchers say, the degus can move the rake as smoothly and efficiently as croupiers in any Las Vegas casino.
This is first time rodents have been trained to wield tools, said Atshushi Iriki, a neuroscientist, who led the experiments at the Laboratory for Symbolic Cognitive Development at the Riken Institute in Tokyo. But other species may soon join them.
While it has long been thought that tool use is a hallmark of higher intelligence, Dr. Iriki said, the brain structures that underlie such abilities may lie dormant in many animals with good hand-and-eye or paw-and-eye coordination. Training them to use tools in captivity provides insights into the plasticity of their brains, he said, and may shed light on how early humans evolved tool use in the first place.
A high degree of sociality also probably makes a difference to the ability to learn these behaviors.
In separate studies, they are examining gene expression in the brains of macaques and marmosets trained to use tools.
Scrub jays scrub breakfast
This is interesting:
Scientists had previously placed the skill of "future-planning" into the exclusively human category. Recent studies have revealed some planning smarts in primates such as apes, but most other animals were perceived as only capable of putting their immediate needs on center stage.
Nicola Clayton et al. rigged it so that some scrub jays had a diet that was predictable in certain ways:
On alternate mornings for six days, eight scrub jays experienced one of two compartments. In one compartment, the birds were always given breakfast, and in the other they were not.
In the evening, after this training period, the scientists allowed the birds to feast freely on pine nuts, which are suitable for hoarding. The birds planned for a breakfast-free morning by hiding much more food in the bare compartment compared with the "breakfast" one. The prudent squirreling away reveals an understanding of future needs, the researchers say.
In a similar experiment, the scrub jays hung out in either a compartment with peanuts or one with dog kibble on alternate mornings. After several days, the birds were allowed to travel between compartments. This time the forward thinkers planned for a balanced diet and buried peanuts in the kibble enclosure and kibble in the peanut compartment.
Thoughts:
1. There are plenty of people willing to argue that Neandertals couldn't do this kind of planning. That's clearly wrong -- planning isn't all that difficult under the right informational circumstances. The birds surely aren't alone, although their caching behavior does prime them for diet-relating planning.
2. Here, the utility of planning is not only to ensure adequate total food intake, but also to enable a better balance of different foods. From the standpoint of nutritional ecology, it makes sense that an animal would be adapted to plan its activities to broaden diet, where possible. This also is very relevant to early hominids.
How carnivorous were cave bears?
Charles Q. Choi reports on a new paper by Michael Richards and colleagues:
For the past 30 years, studies of their skulls, jaws and teeth suggested cave bears might have been largely herbivorous. In addition, the bones of central and western European cave bears matched those of vegetarians in having low levels of nitrogen-15, whose atomic nucleus has one more neutron than common nitrogen-14 does. Animals accumulate nitrogen-15 in their bodies, and animals that eat animals -- that is, carnivores -- build up more nitrogen-15 than herbivores do.
Still, black bears and brown bears are omnivores. This suggested that although some cave bears were largely vegetarian, others might have been more carnivorous.
New data from the Pestera cu Oase ("Cave with Bones") in the southwestern tip of the Carpathian mountains in Romania now hints most of its cave bears were significantly carnivorous, due to their high nitrogen-15 levels.
It's PNAS, so we won't see the paper for a while. I'll comment more fully here when it is available. Nitrogen-15 is the primary evidence for Neandertal carnivory also, although as I've noted (here and here), those interpretations face some complications.
A large source of nitrogen-15 is fish, which seems a likely source for the cave bears.
UPDATE (2008/01/08): I got the paper. The results show that the Oase cave bears have nitrogen-15 values ranging from a low overlapping with red deer up to a high midway through the wolves -- where higher means more carnivorous. There was one outlier with a very low nitrogen-15 ratio. The impressive thing is the range of values, which apparently exceeds the ranges in other species.
In comparison with other European cave bear samples, the Oase specimens are not alone in showing evidence of carnivory, but the vast majority of specimens from other sites (n=105) have values in the red deer range or lower.
Axes of variation
The paper suggests that the high nitrogen-15 in the Oase cave bears could not have come from the local ungulates (red deer and ibex) because their carbon-13 ratios are extremely different from those species. I think that's a fair speculation, but really there are too many dietary parameters to get an estimate from these two ratios. For example, a primarily vegetarian diet that included a significant amount of fish might explain both ratios (and the wide variation in nitrogen-15, since bears compete for fishing access).
But there are other possible axes of variation. Life history and behavioral variation can affect the isotope ratios. Some of the cave bears across Europe have very low (lower than ungulate) nitrogen-15 values. Hibernation has been suggested previously to explain the correlation of nitrogen-15 values with estimates of temperature, the idea being that bears facing colder winters are dormant for longer periods.
The hibernation story raises the question of the impact of long-term climate change on isotope ratios. The channel through which climate changes may affect the uptake of different isotopes into plants and animals is unclear -- it seems to involve temperature and rainfall as they modulate diet availability. Here's a chart of the carbon and nitrogen stable isotopes in Pleistocene Europe in three different carnivores:
Carbon (top) and nitrogen (bottom) stable isotopes in European herbivores (horse, cattle, and deer) over time. Figure 1 from Hedges et al. 2004.
None of this casts any doubt on the paper's results -- the Oase cave bears simply seem to have been higher on the food chain than most other cave bears sampled across Europe. I just raise them to note the demands that paleoecologists are placing on these isotope ratios. Especially when the species in question has substantial dietary flexibility, like bears, we should probably figure that diet choices are the largest component of variation. That means that we should probably be skeptical about the impact of smaller-scale variations, such as climate, unless there is very strong evidence for dietary stability over the relevant time scales.
Since many large European mammals were undergoing large range contractions or extinctions during this time period, we should expect that the surviving species may have undergone substantial changes in niche partitioning and dietary choices. Humans -- whose isotope ratios are in many ways the most interesting -- would be included in this number.
Bear paleoecology
I think the best passage from the paper is the end of the discussion, where the authors compare the dietary and ecological flexibility of extant ursids as a way of contextualizing the cave bears.
As a consequence of these 15N values, the dietary ecology of modern, higher-latitude bears (excluding polar bears) is relevant for that of cave bears, especially the North American brown bears (U. arctos, including the Kodiak and grizzly bears) given their high-latitude range, body-size variation, occupation of regions with less human ecological impact than most of Eurasia, and extensive database. Brown bear diets range from almost completely vegetarian, including ones with substantial amounts of fruit/berries, to ones containing a substantial amount of fish and/or ungulate meat (19-21, 29, 30, 44, 45). All aspects of their omnivorous diets have limitations in availability, potential feeding rates, and nutritional value in any given environment; adequate weight gain for survival, reproduction, and hibernation therefore depends on a mix of as many food resources as are available (19, 21). Meat consumption, in particular, varies widely among and within brown bear populations, due, among non-maritime bears, to the availability of ungulate fauna (29, 30, 44, 45). Large adult males also appear to be more carnivorous than females or subadult bears (28, 29). North American black bears (U. americanus) appear to have similar plant/meat dietary proportions as brown bears (29), except that the larger brown bears are frequently more carnivorous when the prime meat is maritime (e.g., salmon) (46). This ecological flexibility of modern brown bears therefore makes an appropriate model to understand the range of isotopic values now available for European cave bears, both within and between site-specific samples (Richards et al. 2008:4).
Europe presents a problem of bear competition similar in many ways to the current North American case, in that different ecologically flexible species are differentiated by size. In North America, the larger brown bears exclude access to salmon fishing sites from the smaller black bears.
But in Europe, the brown bears were the smaller species. That helps to make sense of the isotope results on Pleistocene European brown bears, which have even lower nitrogen-15 values than the cave bears (Bocherens et al. 2004).
As for the cave bears, I suppose not even pic-a-nic baskets are out of the question....
A genetic afterthought
There is also this:
Genetic Affinities. To provide additional confirmation of the morphological evidence, mitochondrial DNA (mtDNA) was extracted, amplified, and sequenced from 19 ursid samples (SI Table 2). All 19 individual sequences of the Peçstera cu Oase ursids show clear affinity to central European cave bear sequences (35) rather than to brown bears. They do not form a monophyletic group within cave bear mtDNA variation, and the range of the Oase bear haplotypes is spread throughout most of the variability known for central European cave bear populations from southern Germany, Austria, Croatia, and Slovakia (35-37).
If we expect to have any hope of working out the phylogeography of ancient humans (like Neandertals), then we have to be able to work out the movements of many ancient mammals. That's the only chance of cross-The cave bears look a bit like the Neandertal pattern -- probably not surprising since they are both medium-bodied omnivorous mammals. That's encouraging.
References:
Bocherens H, Argant A, Argant J, Billiou D, Crégut-Bonnoure E, Donat-Ayache B, Philippe M, Thinon M. 2004. Diet reconstruction of ancient brown bears (Ursus arctos) from Mont Ventoux (France) using bone collagen stable isotope biogeochemistry (13C, 15N). Can J Zool 82:576-586.
Hedges REM, Stevens RE, Richards MP. 2004. Bone as a stable isotope archive for local climatic information. Quatern Sci Rev 23:959-965. doi:doi:10.1016/j.quascirev.2003.06.022
Richards MP, Pacher M, Stiller M, Quilès J, Hofreiter M, Constantin S, Zilhão J, Trinkaus E. 2008. Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Peçstera cu Oase, Romania. Proc Nat Acad Sci USA (online early) doi:10.1073/pnas.0711063105
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks