culture

Wired's science blog has a piece on cetacean culture and communciation: "Whales might be as much like people as apes are". Dalhousie University researcher Hal Whitehead and his students are the center of the story:

“My strong suspicion is that a lot of sperm whale life revolves around social issues,” said Whitehead. “They’re nomadic, live in permanent groups, and are dependent on each other for everything. Social structure is vital to them. The only constant thing in their world is their social group. I’d guess that a lot of their life is paying attention to social relationships.”

These relationships would be “interestingly different from ours, for a variety of reasons,” continued Whitehead. “There’s nowhere to hide, they can use sound to form an image of each other’s insides — whether you’re pregnant, hungry, sick. In a three-dimensional habitat, it’s probably much harder to say something is mine, or yours, whether it’s a piece of food or a potential mate.”

On the topic of cognitive prerequisites for tool use, the cetaceans seem another very interesting case. Opportunities for material culture are extremely limited (pretty much, sponge-manipulation by dolphins). Yet, other cetaceans have complex foraging behaviors (bubble-netting, for example) that rival the complex plant preparation we see in gorillas, who otherwise use tools rarely.

I've had this paper about "adoption speed" and cultural tastes on my desktop for more than a month, meaning to write something about it. Here's the abstract:

Products, styles, and social movements often catch on and become popular, but little is known about why such identity-relevant cultural tastes and practices die out. We demonstrate that the velocity of adoption may affect abandonment: Analysis of over 100 years of data on first-name adoption in both France and the United States illustrates that cultural tastes that have been adopted quickly die faster (i.e., are less likely to persist). Mirroring this aggregate pattern, at the individual level, expecting parents are more hesitant to adopt names that recently experienced sharper increases in adoption. Further analysis indicate that these effects are driven by concerns about symbolic value: Fads are perceived negatively, so people avoid identity-relevant items with sharply increasing popularity because they believe that they will be short lived. Ancillary analyses also indicate that, in contrast to conventional wisdom, identity-relevant cultural products that are adopted quickly tend to be less successful overall (i.e., reduced cumulative adoption). These results suggest a potential alternate way to explain diffusion patterns that are traditionally seen as driven by saturation of a pool of potential adopters. They also shed light on one factor that may lead cultural tastes to die out.

OK, so the basic idea is that people can tell when something is getting popular really fast, and they start to be less and less likely to adopt the trend. The study doesn't directly address whether that might be due to the availability of copycats -- once "Braden" gets popular enough, people start to divert to sound-alike names like Jayden, Aidan, and Kayden. I wonder how much companies actively try to invoke this process -- how much of an opening is there for a Microsoft Zune or Palm Pre from those who might sense the Apple iPod or iPhone growth has been too fast? And how much of a "slow build" happens because you build the appearance of "classic style" as opposed to fad. I remember how fast people stopped wearing "Jams" by 1990, whereas the Gap seems to have single-handedly generated a never-ending trend of khaki.

One interesting thing is that just after this paper came out, WolframAlpha went public. And you can basically do all the research for the paper on that interface with a simple one-phrase search. For example, here's a search result for the historical popularity of my twins' names in the U.S.:

Oh, yes. That's quite a time-waster we have there.

References:

Berger J, Le Mens G. 2009. How adoption speed affects the abandonment of cultural tastes. Proc Nat Acad Sci USA (early online) doi:10.1073/pnas.0812647106

Fig. 20 from Darwin 1872. "Terror"

While I was out of town for the holidays, a news story by Jeanna Bryner reported on research that looked at the facial expressions of blind Paralympians:

The analyses showed sighted and blind individuals modified their expressions of emotion in the same way in accordance with the social context. For example, in the Paralympics, the athletes competed in a series of elimination rounds so that the final round of two athletes ended in the winner taking home a gold medal while the loser got a silver medal.

The blind silver medalists who lost their final matches tended to produce "social smiles" during the medal ceremonies. Social smiles use only the mouth muscles. True smiles, known as Duchenne smiles, cause the eyes to twinkle and narrow and the cheeks to rise.

The "social smile" is interesting because it seems like a way of concealing emotions from others. The conclusion was that visual learning could not account for the socially correct use of these expressions, since people blind from birth follow the same rules.

When I read this story, I couldn't help but reflect on Darwin's description of facial expressions, in The expression of the emotions in man and animals. By taking up this topic, Darwin set out on new mode of psychological investigation, distinct in many ways from the experimental psychology tradition. In fact, the major figures in German experimental physiology, such as Wundt, are never mentioned in Expression. This clean separation may have been Darwin's deliberate attempt to establish psychological inquiry on new ground; his intent was marked in the last section of the Origin:

In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history (Darwin 577-578).

Darwin was not alone in pursuing a comparative approach and insisting on continuities between humans and other animals. In some details he followed Herbert Spencer's psychology. George Romanes picked up Darwin's own notes on animal behavior as he began to systematize the field; his Animal Intelligence ranged in its examples from invertebrates to man's best friend, the dog.

Darwin also spends substantial parts of Expression on the expressions of dogs. His analysis, like his description of sexual selection in The descent of man presages later work on signaling. But Darwin's human examples are some of the most interesting in the book. The picture at the top of this post was drawn "from a photograph by Duchenne" -- the same Duchenne (Guillaume-Benjamin-Amand de Boulogne) whose name is commemorated by the "Duchenne smile" as well as the eponymous muscular dystrophy. Duchenne was an experimental physiologist, who among other things used electrical stimuli to contort the facial muscles into their characteristic expressions.

Darwin used the photograph above in Expression, along with others of the same experimental subject. The experimenter at right is Duchenne.

Darwin had other means of obtaining information that the current researchers of Paralympians lack. For instance:

Dr. W. Ogle observed for me in one of the London hospitals about twenty patients, just before they were put under the influence of chloroform for operations. They exhibited some trepidation, but no great terror. In only four of the cases was the platysma visibly contracted; and it did not begin to contract until the patients began to cry. The muscle seemed to contract at the moment of each deep-drawn inspiration; so that it is very doubtful whether the contraction depended at all on the emotion of fear. In a fifth case, the patient, who was not chloroformed, was much terrified; and his platysma was more forcibly and persistently contracted than in the other cases. But even here there is room for doubt, for the muscle which appeared to be unusually developed, was seen by Dr. Ogle to contract as the man moved his head from the pillow, after the operation was over. (Darwin 1872:300-301).

His subsequent discussion is interesting, begun with a characteristic Darwin question: "...I felt much perplexed why, in any case, a superficial muscle on the neck should be especially affected by fear...."

Darwin particularly sought to distinguish the unconscious signs of emotions from the deliberate, and the culturally variable from the universal. In a time when the study of cultural variability was just beginning, Darwin does an admirable job.

His explanations of unconscious expressions presage some of the writings of behaviorists, notably John Watson:

Through steps such as these we can understand how it is, that as soon as some melancholy thought passes through the brain, there occurs a just perceptible drawing down of the corners of the mouth, or a slight raising up of the inner ends of the eyebrows, or both movements combined, and immediately afterwards a slight suffusion of tears. A thrill of nerve-force is transmitted along several habitual channels, and produces an effect on any point where the will has not acquired through long habit much power of interference. The above actions may be considered as rudimental vestiges of the screaming-fits, which are so frequent and prolonged during infancy.

In this case, as well as in many others, the links are indeed wonderful which connect cause and effect in giving rise to various expressions on the human countenance; and they explain to us the meaning of certain movements, which we involuntarily and unconsciously perform, whenever certain transitory emotions pass through our minds.

Darwin did discuss the issue of Duchenne smiles and false smiles in Expression. Here is a redacted section from pages 203-204:

Dr. Duchenne has given a large photograph of an old man (reduced on Plate III. fig 4), in his usual passive condition, and another of the same man (fig. 5), naturally smiling. The latter was instantly recognised by every one to whom it was shown as true to nature. He has also given, as an example of an unnatural or false smile, another photograph (fig. 6) of the same old man, with the corners of his mouth strongly retracted by the galvanization of the great zygomatic muscles. That the expression is not natural is clear, for I showed this photograph to twenty-four persons, of whom three could not in the least tell what was meant, whilst the others, though they perceived that the expression was of the nature of a smile, answered in such words as "a wicked joke," "trying to laugh," "grinning laughter," "half-amazed laughter," &c. Dr. Duchenne attributes the falseness of the expression altogether to the orbicular muscles of the lower eyelids not being sufficiently contracted; for he justly lays great stress on their contraction in the expression of joy.

He goes on to examine the muscles involved in the expression with more detail. Darwin's concern was to connect the smiles of humans with expressions of other primates, and to connect the actions of the facial muscles in a rational way. For example, Darwin suggested that the zygomatic muscles contract during pleasurable emotions, and attempted to relate the characteristic expressions of mental patients having delusions of grandeur to that pattern. Elsewhere, he examines the "grins" of dogs and their relation to play, as well as various reports of smiles in non-human primates.

So, I doubt Darwin would have been surprised by the research on blind athletes.

References:

Darwin CR. 1872. The expression of the emotions in man and animals. John Murray, London.

Darwin CR. 1869. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. John Murray, London. 5 ed.

If you're looking for a way to waste your time today, you might check out The Economist's online debate, which focuses on the question of whether the world is getting more or less cultured. Or as they put it, "smarting up or dumbing down":

Intelligent Life, The Economist's quarterly sister magazine, has been looking into what is happening to culture in Britain. The editor, Tim de Lisle, presents a mass of evidence that makes a seemingly irrefutable case: all over the country, more people are going to museums, visiting literary festivals and listening to classical music than ever before. If that isn't wising up, it is hard to know what is.

Susan Jacoby, a scholar whose career began as a reporter on the Washington Post and whose writing now focuses on American intellectual history, sees no reason for Westerners to pat themselves on the back. The education bar, in the Anglo-American world, at least, she says, is being set lower and lower. Fewer and fewer people read books; instead they just hoover up information on the internet. After she wrote an article for her former paper on the decline of reading, she received a deluge of emails from people who said they were proud that they never read books at all. They couldn't see the point.

The recurring issue in the debate seems to be whether people are using information in a deeper or more superficial way. Since both these terms are laden with moral value (always better to be deep than superficial, right?), one may wonder whether the real question isn't whether we feel better about ourselves or not.

Indeed, the two participants devolve immediately into schoolmarmy arguments about whether "high culture" is thriving or not. So we have "increasing attendance at museums" on one side the balance and "decreasing market for hardbound fiction" on the other. Blah.

It would be more interesting to consider the biocultural question: If our culture presents us with more information, do we actually get better at using it over time? There's no mention of the Flynn Effect in the debate, but it seems very relevant -- especially considering the worry that the Brits are "dumbing down".

The Chronicle of Higher Education has a long article about the tentative pairing of genetics and sociology. The occasion for the article is a recent issue of the American Journal of Sociology that features studies that combine genetics with sociology in various ways. Some are finding interesting things:

North Carolina's [Guang] Guo looks at a gene that has been tied to levels of dopamine, a neurotransmitter linked to aggressiveness and sexual energy. One variant of the gene, which may tamp down dopamine levels, has a "robust protective effect" against early first-time sex among teenagers, he finds. The protective effect vanishes, however, when teenagers with that genotype find themselves in schools where early sex is the norm. Meanwhile, Bernice Pescosolido, of Indiana University at Bloomington — who, like Guo, has several co-authors — finds that a version of the gene Gabra2, implicated by other researchers in an increased risk for alcoholism, has no effect on women. Even among men, those with the risky version have no increased risk for alcoholism provided they have strong family bonds.

The theme of the article:

The psychologist Avshalom Caspi, with appointments at the University of Wisconsin at Madison and King's College London, has demonstrated that a gene associated with levels of the neurotransmitter serotonin can influence how resilient an individual is in the face of stressful life events. Caspi's widely cited work is nuanced enough to win respect even from genetic skeptics.

It helps, too, that psychologists have turned up "progressive" results. One example is the finding, by the University of Virginia's Eric Turkheimer, that IQ is far less heritable when a child's parents are poor than when they are well off. That kind of stuff goes over well in sociology, a left-skewing field.

Social scientists described in the article yearn to discover that things are "nuanced" or show hidden dependencies to environmental factors. Fair enough -- if you study hammers, why not look for nails? Still, it gets boring to find that every case ends with that "stinger" that shows how environment is the most important thing after all. Heritability is a ratio: If it's nonzero and nonunity, you'll have both environmental and genetic variance.

And some take skepticism to an extreme:

[Troy] Duster recalled sitting on various governmental review boards and watching as what he considered an inordinate amount of money flowed toward geneticists and other scientists who studied maladies like alcoholism. Why spend millions searching for a predisposition to alcoholism among Native Americans, he asked, when their mistreatment and oppression offered explanation enough?

Oh, hey, why spend millions "searching" for a predisposition to Type 2 diabetes, when you know that overeating is explanation enough? That "searching" thing? Some of us like to call that "understanding"! As in, when you understand something, maybe you could do something about it!

Well, it's a long article with a number of references to different research connecting genetics and behavior. Many of the examples have to do with adolescent behavior, because they draw upon the National Longitudinal Study of Adolescent Health, which was designed to examine heritability of various traits.

I think the most important potential of behavioral genetics is to let us understand the normal range of variation of behavior. The examples that look at the different reactions of genetically similar individuals in different environments are very interesting, and certainly confirm the importance of environments in such behaviors. But if we want to understand society, we need to understand how genetically different people tend to behave (or feel) differently in similar environments.

Peter Richerson and Robert Boyd are well-known for their studies of processes of culture change. They apply principles from biological evolution to form hypotheses about changes of cultural traits over time.

In the December 18 issue of Nature, Richerson and Boyd have an essay titled, "Migration: an engine for social change." In the essay, they advance the hypothesis that migration is a "selective" mechanism of social change:

As cultural evolutionists interested in how societies change over the long term, we have thought a lot about migration, but only recently tumbled to an obvious idea: migration has a profound effect on how societies evolve culturally because it is selective. People move to societies that provide a more attractive way of life and, all other things being equal, this process spreads ideas and institutions that promote economic efficiency, social order and equality.

This idea draws from an analogy with the evolutionary mechanism of gene flow. Migration of individuals may cause an adaptive gene from one population to enter another population where it had previously been absent. A population that is a net recipient of gene flow from other regions may thereby receive a large store of alleles for selection later to work upon.

In the context of Premo and Hublin's hypothesis that culture tended to impede migration in the Pleistocene, Richerson and Boyd's model of migration accelerating culture change is an interesting contrast.

Migration rates between historic hunter-gatherer groups were quite high. Minimal bands are exogamous units -- nearly all marriages occur between these small groups. The larger groups made up of several bands -- sometimes called tribes -- are endogamous, but rates of migration between them are nevertheless high. For example, Joe Birdsell estimated intermarriage rates between tribes of Australian hunter-gatherers at 14 percent (that is, 14 percent of marriages involved members of different tribes).

Richerson and Boyd mention migration in small-scale societies (they use the example of Papua New Guinea). But more broadly, they want to apply their idea to the recent large movements of people from poor nations into rich ones:

We believe that immigration generates far more cultural evolution today than does conquest. Flows of migrants are often substantial. Foreign-born people, mainly from Latin America and Asia, compose about 11% of the current US population, a figure close to historical averages. The richer countries of Europe, such as Sweden, Norway and Germany, once the source of streams of immigrants to the United States and elsewhere, are now receiving people from Asia, Africa and poorer European countries such as Poland and the Balkan states.

Eleven percent migrants would be a high value for historic tribes of hunter-gatherers -- where children are perhaps half the population. Considering adults only, it might not be so unreasonable for small-scale societies. If these people transplant successful cultural elements -- effective technologies or ecological knowledge, for example -- then such migration will be an important way of equalizing the cultural adaptation of different societies. In other words, gene flow as applied to ideas.

But I can think of at least two weaknesses with the biological analogy.

1. Gene flow may introduces alleles that would otherwise be absent in a small population. But a very large population would be likely to get those alleles anyway. Likewise, ideas may be subject to diminishing returns: a immigrants might make a large difference to the set of ideas available in a small backwater society, but even a very large store of migrants may make little additional difference to an already-large cosmopolitan society.

2. Cultural "institutions" include things like economic laws, education systems, dispositions of marriages, births and child care obligations, and political structures. Each is an invention involving the interaction of many ideas, and they work to the extent that ideas and behaviors are shared. A relatively small amount of graft and violence, for example in 1920's Chicago, can subvert a political and legal system that depends on widespread honesty and compliance. If we were to think of a biological analogy for such complicated systems, we would probably tend to think of "coadapted gene complexes" -- instances in which the adaptive value of one gene depends on the presence or absence of many other genes. Coadapted gene complexes are instances in which gene flow may not typically lead to any additional power for selection. At an extreme, gene flow may lead to disruptive selection, or reinforcement of slight genetic barriers may enhance or accelerate speciation.

The biological analogy loses force if these weaknesses apply. I tend to think that if we are looking for causes of "cultural evolution," we should attend carefully to cases where biological evolution may lead to similar conflicts where one force (migration) generates opposing effects (adaptive and maladaptive). Sometimes gene flow has a bad outcome -- at least to the extent that "bad" means "lower mean fitness."

In his 2003 book, Historical Dynamics,, Peter Turchin develops a model of culture change that emphasizes group solidarity. Following Ibn Khaldun, Turchin refers to the cohesive character of a group of people as asabiya. In his theory, relatively small societies forming in frontier regions are subject to intense selection. Societies that develop common feeling and solidarity tend to persist; those that remain dissolute tend to be absorbed by larger entities. Over time, a few or a single society may come to dominate a large region -- forming an empire. But these large societies slowly lose their common feeling over time, resulting in their eventual loss of political cohesion and overthrow at the hands of upstart peoples with higher asabiya.

I mention this theory not to explain it in depth, but to point out that it has roughly opposite predictions from the hypothesis Richerson and Boyd propose. In Turchin's model, widespread immigration may follow as a consequence of empire's spread and success, but this immigration is one of several forces that weakens or destabilizes the society. Richerson and Boyd's scenario, in which immigration strengthens a society, would seem relevant in Turchin's model only at times when the society is initially forming.

But immigrants, and their descendants, adopt some of the ideas and institutions that make their new homes better places to live and raise families. This integration promotes the spread of ideas and institutions that encourage order, justice and economic efficiency.

I think that integration is a difficult problem that demands its own solutions -- new ideas and institutions to facilitate the interactions of people who don't have the same background or necessarily the same language. Some societies have made this work, others have not, and they have done so using different ideas and institutions. In particular, "economic efficiency" and "justice" have different relations to immigration in the U.S. compared to Saudi Arabia. Or in the U.S. today compared to the U.S. in 1910. And some nations have made effective use of ideas from other cultures without massive immigration. Japan between 1860 and 1930 and Britain between 1700 and 1850 would seem to fall into this category.

We may say that the Chinese unwillingness to adopt Western ideas, trade, and immigration through the early twentieth century had a bad outcome. But are we measuring the outcome in terms of geopolitical position, in terms of the ability of entrenched elites to maintain power and order, in terms of territory? Or in terms of numbers -- something more akin to "mean fitness?"

Ultimately, we evaluate the strength of a hypothesis by its ability to predict or explain empirical evidence. Naturally in an essay of this kind Richerson and Boyd did not have the opportunity to draw in examples in a way that clearly support their hypothesis. But those examples they are able to include seem pretty weak:

Likewise, the growth of ancient empires seems to have owed much to the assimilation of border peoples. Conquering elites, such as the Mongols in China, the Mughals in India and the Goths in Rome, largely adapted to their highly successful host culture rather than the other way around. In every case, these durable systems had institutions — the Confucian merit-based bureaucracy, the Hindu system of self-governing castes, Roman law — that endure today in one form or another.

These examples support the idea that societies that attract immigrants tend to have ideas and institutions that cause them to be richer, less violent and less exploitative than the societies that supply them. The Goths were fleeing chaos on the steppe. Christianity, with its concern for the poor and humble, grew mainly by voluntary conversion to eventually become the official religion in the Roman Empire. Confucian humanism, with its concern for good government, replaced the predatory and quarrelsome landed elite as the backbone of Chinese society. Hindu tolerance and productive organization of cultural diversity led to one of the world's wealthiest societies in medieval times. Medieval Islam attracted converts spanning from North Africa to southeast Asia because it supported effective statecraft, intellectual advancement and trade on a vast scale.

This is a fairly Pollyanna-ish view of the growth of Christianity, Islam, and Confucianism. It seems close to claiming that the Goths were a net benefit to Roman cultural institutions.

Alexander the Great and Genghis Khan were successful conquerors, but they made a less durable impact on the world than, say, Mohammed, Buddha, Christ and the institution builders they inspired such as Constantine and the Umayyad caliphs.

Maybe there is a case here somewhere, but I'm not sure Constantine is really the example they wanted.

A good cultural conservative would point out that there is no surprise when an effective cultural institution survives for a long time. Effectiveness causes persistence. Random changes that affect the function of a long-lasting institution are likely to be bad. An institution that can tolerate changes in other cultural parameters (one that is modular) will tend to persist in the face of other changes -- like the substitution of an imperial elite for that of a conquering horde. Conquering hordes from the hinterland didn't come fully equipped with cultural mechanisms to govern cities, tax commerce, and ensure agricultural productivity. Of course they would have adopted the trappings of the empires they conquered.

Like biological adaptations, we should be skeptical that changes would make long-lasting cultural institutions more effective. We can also consider that their continued effectiveness depends on many other shared aspects of culture.

References:

Richerson RJ, Boyd R. 2008. Migration: an engine for social change. Nature 456:877. doi:10.1038/456877a

This is a complicated story with many interlocking parts. Telling the whole story may well take me fifty posts. There's a lot of new science hiding in here waiting to get out.

I'm starting now because of the new paper by Luke Premo and Jean-Jacques Hublin, titled "Culture, population structure, and low genetic diversity in Pleistocene hominins." This paper is not the final word on its topic, nor is it the first word. But it is very much worth reading.

It makes an excellent point of departure to explain what we know and don't know about the genetics of prehistoric humans. Premo and Hublin propose an interesting model with interaction between culture and natural selection, as an explanation for a 35-year-old problem in human evolution: Our low level of genetic variation.

Their model may be right. I certainly think there's a kernel of truth in it, shared with a number of other models, as I'll describe below. And it's testable -- a project to which we'll be returning in the next few months.

In last week's Science, Stanislas Dehaene and colleagues describe the relation of cultural invention to "universal intuition" about mathematical logic:

The mapping of numbers onto space is fundamental to measurement and to mathematics. Is this mapping a cultural invention or a universal intuition shared by all humans regardless of culture and education? We probed number-space mappings in the Mundurucu, an Amazonian indigene group with a reduced numerical lexicon and little or no formal education. At all ages, the Mundurucu mapped symbolic and nonsymbolic numbers onto a logarithmic scale, whereas Western adults used linear mapping with small or symbolic numbers and logarithmic mapping when numbers were presented nonsymbolically under conditions that discouraged counting. This indicates that the mapping of numbers onto space is a universal intuition and that this initial intuition of number is logarithmic. The concept of a linear number line appears to be a cultural invention that fails to develop in the absence of formal education (Dehaene et al. 2008:1217).

The idea is that children in Western societies have to learn that a number line is a linear representation; they begin by compressing the space devoted to large numbers:

When asked to point toward the correct location for a spoken number word onto a line segment labeled with 0 at left and 100 at right, even kindergarteners understand the task and behave nonrandomly, systematically placing smaller numbers at left and larger numbers at right. They do not distribute the numbers evenly, however, and instead devote more space to small numbers, imposing a compressed logarithmic mapping. For instance, they might place number 10 near the middle of the 0-to-100 segment. This compressive response fits nicely with animal and infant studies that demonstrate that numerical perception obeys Weber's law, a ubiquitous psychophysical law whereby increasingly larger quantities are represented with proportionally greater imprecision, compatible with a logarithmic internal representation with fixed noise (7, 20, 21). A shift from logarithmic to linear mapping occurs later in development, between first and fourth grade, depending on experience and the range of numbers tested (17-19).

They note that there's a problem testing these ideas in Western children, who are surrounded throughout their development by numbers -- in books, "elevators" and other places. Most of these numbers are small ones -- especially one through ten -- so they might naturally accentuate the ones they know.

They found when testing the Mundurucu that both adults and children tended to compress the high end of the number scale, even testing numbers between one and ten. This compression is logarithmic -- they accentuate contrasts between small numbers disproportionately. It makes sense logically -- we care more about detailed contrasts between small numbers than large numbers. They don't give an idea of which logarithm people are using; and in fact it may be different ones for different people. The important fact is the small number/large number contrast.

Dehaene and colleagues attribute this scaling to mapping at the neural level:

What are the sources of this universal logarithmic mapping? Research on the brain mechanisms of numerosity perception have revealed a compressed numerosity code, whereby individual neurons in the parietal and prefrontal cortex exhibit a Gaussian tuning curve on a logarithmic axis of number (27). As first noted by Gustav Fechner, such a constant imprecision on a logarithmic scale can explain Weber's law -- the fact that larger numbers require a proportional larger difference in order to remain equally discriminable. Indeed, a recent model suggests that the tuning properties of number neurons can account for many details of elementary mental arithmetic in humans and animals (21). In the final analysis, the logarithmic code may have been selected during evolution for its compactness: Like an engineer's slide rule, a log scale provides a compact neural representation of several orders of magnitude with fixed relative precision.

From that perspective, the Western conception of the number line appears as a very distinctive invention, capable of adjusting the logarithmic encoding to arrive at faster and more accurate mathematical conclusions about large numbers. The authors speculate that addition and subtraction (which display invariance between large and small numbers) and experience with measurement underlay the development of the linear concept in Western children.

References:

Dehaene S, Izard V, Spelke E, Pica P. 2008. Log or linear? Distinct intuitions of the number scale in Western and Amazonian indigene cultures. Science 320:1217-1220. doi:10.1126/science.1156540

The June Scientific American (no link available) has an article on page 32 about the "therapeutic value of blogging." That's some relief, after the stories a couple of months ago about blogging being potentially deadly.

And it's no small irony, considering that the article I found on the previous two pages had great potential to give me therapeutic opportunities here.

In the article, titled, "Need for speed?" David Biello wrote up some of the human genetics results of the past 6 months, placing them as a point-counterpoint presentation of our acceleration result.

First, he cites Gregory Cochran, who does as good a job explaining our result in one sentence as I've seen:

"We found very many human genes undergoing selection" ... "We believe that this can be explained by an increase in the strength of selection as people became agriculturalists, a major ecological change, and a vast increase in the number of favorable mutations as agriculture led to increased population size."

In that form, it is hard to see how anyone could disagree. Clearly, agriculture was a major ecological shift for humans, and it imposed new selection pressures associated with diet, disease, social organization and other ecological factors. At the same time, the population grew and more people meant more mutations. That's the story; the rest is detail filled in by anthropology, genomics, and math.

Biello then cites another recent study that partially confirms our results. That study, by Lluis Quintana-Murci and colleagues, found a much smaller number of selected genes (55), but what is important is that every one of these genes has an F_ST greater than 0.65. In other words, in every one of these cases, an allele that is vanishingly rare in most of the world has reached a frequency over 80 percent in one population. As allele frequencies go, these are extreme differences -- much, much larger than the average genetic difference between populations, characterized by an F_ST around 0.1. We also found a few such alleles in our survey of selected genes, but the vast majority of genes have not generated such extreme differences in frequency -- mainly because they haven't been around long enough. In other words, the Quintana-Murci study confirms the distribution of positively selected alleles, across the range where it overlaps with other studies, including ours.

Then Biello turns to the doubters. Noah Rosenberg coauthored a study earlier this year that reported polymorphism data from a sample of populations around the world.

"We are a young species," remarks geneticist Noah Rosenberg of the University of Michigan at Ann Arbor, who participated in a comprehensive study of genetic variation that appeared in Nature in February. "Different human populations have not been separated for long enough periods of time to develop their own new alleles."

Now, I never hold quotes in the press against people, because they represent a very small portion of what they may have said to a writer, and there are many opportunities for miscommunication. Still, I have to write about this, because it's about my work! So I'll try to describe the misconceptions illustrated by the article.

I am pretty sure that Rosenberg must know that his statement in the article is false. For one thing, "developing" a new allele is simply mutation, and mutation occurs continuously. All human populations have rare alleles that have originated recently and remain distributed only across small areas. Rosenberg's surveys of gene variation have identified many such alleles.

But more important to the current question, positive selection carries an allele to high frequency very rapidly -- much more quickly than the 50,000-year or longer span of time we are talking about. An allele with a five percent fitness edge can go from zero to fixation in several hundred generations -- in humans, they can make very large frequency changes in a thousand years.

If we took the quote at face value, Rosenberg would be saying that human evolution is impossible -- and that new selected alleles like lactase persistence and sickle cell simply cannot exist. We may be a young species (although I would argue the point), but that doesn't mean that we have stopped evolving!

Two prominent geneticists quoted in the article suggest that a bottleneck may explain the pattern of human genetic variation. Here also, I have to be cautious interpreting their quotes -- because even though they may seem relevant, they are referring to their own research papers, which don't actually address the question of linkage disequilibrium and positive selection.

Marcus Feldman suggests that a series of bottlenecks are a likely explanation for the pattern of human genetic variation, in particular, the decreasing gradient of genetic diversity with increasing distance from Africa. This is the "serial founder effect" scenario that I have written about before. I criticized Feldman's and other papers on this subject this spring, referring to "the Stanford school of genetic orthodoxy." My basic point is that all of the results are assumed to support the idea of bottlenecks: no one has yet tested the hypothesis. Even simulations that show the credibility of the concept do not test the hypothesis, because they do not examine credible alternatives, either demographic or selective.

More important, bottlenecks during the dispersal from Africa 50,000 years ago cannot possibly explain linkage blocks concentrated in coding genes with a mean age of 5500 years!

Why is there such difficulty understanding natural selection? I find it quite incredible that many of the scientists who would rail against ignoring Darwin in public schools at the same time actively root out Darwin's theory from their graduate students. Still, there it is. One prominent geneticist (I won't give the name) recently asked me, "You don't really think that lactase was selected, do you?" Many really believe that natural selection has stopped and that recent human evolution reflects nothing more than the cumulative effects of bottlenecks.

What is amazing to me is that these same geneticists embrace hypotheses of population history that cannot possibly have happened. The other geneticists quoted in the article, Carlos Bustamante and his graduate student Kirk Lohmueller, wrote a paper earlier this spring arguing that deleterious mutations have reached high frequency in Europeans (moreso than Africans) because of a bottleneck during European history. The press reported this work as "Whites genetically weaker than blacks, study finds." The hypothesis in the paper is that protein-coding sites otherwise conserved in most mammals may differ among humans because of relaxed selection in a bottleneck.

Here's why they're wrong: their bottleneck is impossible. They propose that the European population was a small, isolated population of 5,700 effective individuals from 214,000 years ago up to the Last Glacial Maximum. I suppose I should take some encouragement that they believe Neandertals were European ancestors (because otherwise, where exactly would this small, isolated population of Europeans have lived). But it's still quite impossible -- it implies no gene flow between Africans and Europeans across that entire span. You see, that is the only way that genetic drift can lead to this kind of result -- large differences in frequencies between continents for hundreds of deleterious alleles. It takes a bottleneck of exceptional length, along with complete isolation.

In what has become a troubling trend, these details were hidden away in the online supplementary information of the paper. It is no surprise that most people read only the paper's conclusions, without critically evaluating the methods. But when the assumptions are hidden so that it takes an effort to look at them, you can understand that the paper does not receive the kind of scrutiny that it deserves. These are not obscure laboratory techniques; they are the basic evidence on which the conclusions were based.

Now, Bustamante knows that positive selection has been very important in recent human evolution, because he wrote an important paper on the subject in 2005. I wrote about the paper at the time -- it was one of the works that really got us thinking about acceleration in the first place. So why in the world did their more recent paper adopt such a ridiculous model of population history?

In any event, I don't think that either of these studies from earlier this year are relevant to our acceleration results. They address different aspects of genetic variation. However, acceleration may help to explain the high frequencies of some gene variants conserved in other mammals -- the results explained by Lohmueller and colleagues as relaxed selection under a bottleneck.

The acceleration of recent positive selection would predict that many otherwise conserved gene variants may be segregating in humans, because they are the targets of positive selection. These conserved sites are among those most likely to show a strong sign of recent selection, because adaptive changes on them are necessarily rare (we know they're rare, because they haven't happened very often among other species). Most such sites are still conserved in humans -- it's just not possible to change their function in adaptive ways. But the massive ecological changes of recent human history have created the opportunity for adaptive responses that are not present in other mammalian lineages. We shouldn't be surprised to see that some such changes are currently underway.

Now, that's a different interpretation of the same data, and it's a testable hypothesis. Are these conserved sites in regions that show other signs of positive selection? If they are, then acceleration explains the data. I'm looking into it now.

I'm doing some research for an essay, which relies quite a bit on the work of Dobzhansky and a few of his contemporaries. There are some great quotes that I won't be using, but thought it would be worth passing on. Probably to the greatest extent among the architects of the Synthesis, Dobzhansky concerned himself with the relationship between genetic evolution and human cultural evolution.

In 1963, he published an essay in Current Anthropology addressing the relationship of anthropology and the natural sciences -- part of a forum that also addressed the relation of anthropology with the social sciences and humanities.

Man is a highly variable polytypic and polymorphic species. The genetic variability affects behavioral traits no less than physiological and structural ones, and it is false to imagine that these three categories are clearly separable. The chief reasons why so many people are loath to admit the genetic variability of social and culturally significant traits are two. First, human equality is stubbornly confused with identity, and diversity with inequality, as though to be entitled to an equality of opportunity, people would have to be identical twins. Human diversity is not incompatible with equality. Secondly, it is futile to look for one-to-one correspondence between cultural forms and genetic traits. Cultural forms are not determined by genes, but their emergence and maintenance are made possible by the genetically conditioned human diversity. The division of labor in human societies is primarily a cultural rather than a genetic phenomenon, but could it be sustained in a population consisting of persons genetically as similar as identical twins? This is not entirely a vain question, since at least one great geneticist has recently envisaged the possibility of bringing about such genetic uniformity (Dobzhansky 1963:147).

Later in the essay, Dobzhansky raised the problem of an excess of success -- namely, that human population growth and technology made it possible to avoid mortality that once selected against various "bad" genes. Various beliefs about this trend gave the impetus to early-20th-century eugenics, and were a continuing concern for "well-thinking" people. Would humans become victims of their own success? Dobzhansky responded in two ways. First, by noting that natural selection is hardly a savior:

Neither do I need to retell here the story of the alleged relaxation or suspension of natural selection in civilized mankind. The dangers from this source, although not necessarily exaggerated, have often been presented in a wrong perspective. A notion, which is less frequently stated explicitly than implied in many writings, is that the progress of mankind would be safe and even irresistible if only the natural selection were permitted to operate unobstructed by civilization and its amenities. This notion does not stand critical examination. Natural selection does not even insure that the species on which it acts will survive, let alone that it will improve, in any sense of the word "improvement." Dinosaurs became extinct, despite their evolution having been piloted by natural selection, quite unhampered by culture, medicine, or charity (Dobzhansky 1963:148).

Second, Dobzhansky addressed the real question: whether the current direction of genetic change is desirable:

Reproductive fitness is assuredly not the only virtue which we admire in men and would like them to possess. By its maintenance of the reproductive fitness, natural selection brings results which we, men, do not necessarily hold desirable. But to say that natural selection is suspended in mankind because we are not sure that man's biological evolution has assumed a direction to our liking, is to make the word "natural" selection biologically meaningless. Natural selection is automatic, mechanical, blind. It has brought about the evolution of the living world and the emergence of man with his capacity for culture, but it has no purpose because purposes are human prerogatives (Dobzhansky 1963:148).

He ends the essay on the most remarkable note -- well, read it for yourself:

Being an anthropologist only by avocation, I may perhaps venture to claim for anthropology more than most anthropologists dare claim for themselves. The ultimate function of anthropology is no less than to provide the knowledge requisite for the guidance of human evolution (Dobzhansky 1963:148).

Shades of Hari Seldon, to be sure, but especially humorous in light of later events in the field. Still, one wonders how an anthropology directed toward this goal would be organized...

References:

Dobzhansky T. 1963. Anthropology and the natural sciences -- the problem of human evolution. Curr Anthropol 4:138+146-148.

Current Biology is running an interview with biologist and Mutants author Armand Leroi. I found this part interesting:

What important questions remain to be answered in your field? I can think of two. The first is: can we predict the course of organic evolution in the long term? The short term is easy: that's just the breeder's equation. But understanding the longue durée requires a theory that predicts what phenotypes mutation will produce. I am, of course, talking about 'the correlation of parts', 'developmental constraints', 'mutational bias', the 'integration of development with evolution', 'the real reason pigs can't fly' -- every generation since Darwin has considered, and failed to solve, the problem, though they've usually given it a new name.

The second question is rather like the first: can we predict the course of cultural evolution in the long term? (One might add: or even in the short term?) Darwin saw the analogy between cultural and organic evolution; theoretical population geneticists worked out the mathematics of the transmission of cultural traits years ago. Despite this, the field really didn't take off. I think it is taking off now. Culture is the New World of evolutionary science. To be sure, anthropologists discovered it long ago, but rather like Vikings in America, they never made much of what they found.

Well, I suppose nobody ever accused Kroeber of being Hari Seldon, but to anyone knowledgeable in the least about anthropology, this last remark seems a little dippy. Cultural evolutionist theories have come into fashion several times in the last 150 years. The reason that evolutionist ideas tend to go out of fashion is that they really fail to predict any particulars. Now, maybe somebody will find a way to do better, but I'd say any would-be Columbus has some pretty steep problems to overcome.

References:

Leroi, A. 2007. Q & A. Curr Biol 17:R619-R620. doi:10.1016/j.cub.2007.06.006

Ann Gibbons reports on the upcoming article in Current Biology:

[Jill] Pruetz's team, working at the Fongoli research site in the wooded savanna of Senegal, observed chimps breaking off green branches and in four cases using their incisors to sharpen the points. The chimps, which typically weigh 26 to 60 kilograms, were hunting nocturnal bush babies, 100- to 300-gram primates that hide by day in holes in trees. In all, Pruetz and Paco Bertolani, a graduate student at Cambridge University, documented 10 different chimps thrusting the tools into holes in 22 instances. "This is habitual," says Pruetz, whose team logged 2500 hours of observations.

Sucks to be a bush baby.

References:

Gibbons A. 2007. Spear-wielding chimps seen hunting bush babies. Science 315:1063. doi:10.1126/science.315.5815.1063

Here's a LiveScience story by Heather Whipps, about the discovery of chimpanzee nutcracking stones dating back to 4300 years ago:

Though there were no chimpanzee remains at the settlement, testing by archaeologists revealed the tool-laden camp was most likely used by the Great Ape. The stones were much bigger than anything a human could use comfortably and bore the residue of nuts that modern chimpanzees like to snack on.

"This is the only case of any prehistoric, non-human Great Ape tool use ever discovered," [archaeologist Julio] Mercader told LiveScience.

That's very cool. The news piece claims that this is great vindication for the idea that chimpanzees developed this ability without exposure to humans. That is, some people had argued that chimpanzees might have been "acculturated" to crack nuts by watching nearby people. Personally, I never thought there was much to that idea, since nutcracking is so widespread among chimpanzees and clearly learned by chimps with minimal or no human contact.

The most interesting part to me is the possibility that archaeologists will develop a search strategy for stone tools older than flaked stone tool manufacture.

The NY Times writer Benedict Carey has an interesting short article about research into repressed memories. There is a group of researchers who claim that the phenomenon is a cultural construct that emerged very recently:

In a paper posted online in the current issue of the journal Psychological Medicine, a team of psychiatrists and literary scholars reports that it could not find a single account of repressed memory, fictional or not, before the year 1800.

The researchers offered a $1,000 reward last March to anyone who could document such a case in a healthy, lucid person. They posted the challenge in newspapers and on 30 Web sites where the topic might be discussed. None of the responses were convincing, the authors wrote, suggesting that repressed memory is a "culture-bound syndrome" and not a natural process of human memory.

They're saying that the character Madame de Tourvel in Naturally, other researchers dispute the idea -- some even claim to have evidence from ancient Greek literature.

If I have an informed opinion, I've repressed it. But what I find interesting is the idea that a popular literary trends lead scientific research, sometimes to wrong results. It may be hard to rule out that something imagined in fiction could actually happen -- think of the number of people who have tried to find loopholes in special relativity that could lead to faster-than-light travel. There was no science fiction in 1800, but developing ideas about the mind provide their own equivalent.

We know that science can proceed along a false or misleading path for a long time when the cultural biases of the scientists lead research. Fictional plot devices are clever just insofar as people are willing to "suspend disbelief" about them -- which is a function of the readers' cultural biases. So the two combined might make for some interesting history!