Female brains and male skin tone

It is well known that women feel attracted to certain visual, auditory, and olfactory characteristics of men. This attraction seems to be hormonally regulated, as suggested by psychosexual studies of women at different phases of the menstrual cycle. In general, women are more strongly attracted to male characteristics during the estrogen-dominant phase of their cycle (first two-thirds) than during the progesterone-dominant phase (last third).

This cyclical change has been most recently shown by Rupp et al. (2009). MRI scans were used to measure how female brains process pictures of male faces that morphing software had either masculinized or feminized. The subjects were tested on days 10-12 and days 19-23 of the menstrual cycle. Measurements were taken of their levels of estradiol, progesterone, free testosterone, and total testosterone. The subjects also filled out questionnaires about their psychosexual profile (propensity for short-term sexual encounters, for sexual excitation, for sexual inhibition, etc.).

During the first time window (days 10-12), five brain regions showed a stronger neural response to masculinized faces than to feminized faces. No brain region showed the reverse pattern. During the second time window (days 19-23), only one region responded more to masculinized faces than to feminized faces. For both windows, some regions showed significant correlations between neural activation and hormone level. Estradiol correlated positively with neural activation whereas progesterone correlated negatively. The correlations were negative or positive for free and total testosterone. In some brain regions, neural activation also correlated with psychosexual variables.

What was driving these neural responses? What facial feature was turning these women on? In response to an e-mail, the lead author, Heather Rupp, told me that the morphing software had varied the shape of the male faces and their skin tone. The masculinized faces were darker-skinned and the feminized faces lighter-skinned. Her results may thus dovetail with my own findings on female preferences with regard to male skin tone, i.e., my subjects more strongly preferred darker male faces during the estrogen-dominant phase of their menstrual cycle than during the progesterone-dominant phase (Frost 1994).

References

Frost P. (1994). Preference for darker faces in photographs at different phases of the menstrual cycle: Preliminary assessment of evidence for a hormonal relationship, Perceptual and Motor Skills, 79, 507-514.

Rupp, H.A., T.W. James, E.D. Ketterson, D.R. Sengelaub, E. Janssen, and J.R. Heiman. (2009). Neural activation in women in response to masculinized male faces: mediation by hormones and psychosexual factors. Evolution and Human Behavior, 30, 1-10.

Blond Inuit?

One of the mysteries of anthropology is the reported presence of ‘blond’ Inuit in the western Canadian Arctic, specifically on and around Victoria Island. They were first noticed by the explorer Sir John Franklin and by Alaskan whalers.

The travellers who have been most surprised by the appearance of the Victoria Island Eskimos are those who are most used to Eskimos of the regular or “pure” type. Such a party were Klinkenberg’s white and (Alaskan) Eskimo crew of the American whaling ship Olga … and it was through her captain and crew that I first half-realized that the people of western Victoria Island were conspicuously different from other Eskimos. … What half-convinced me that he [the captain] was right was the emphatic corroboration of the Alaska Eskimo members of Klinkenberg’s crew, who said that the Victoria Islanders were in appearance like a group of half-castes, although they were wholly Eskimo in language and customs. (Stefansson, 1908, pp. 375-376)

These impressions were confirmed by the anthropologist Vilhjalmur Stefansson for Victoria Island and by the anthropologist Knud Rasmussen for adjacent islands:

In reality these blond types are not peculiar to Victoria Island. In King William Island and on Back River, as well as on Kent Peninsula, I found types which had exactly the same outward characteristics, the same light complexion, the same reddish or brownish hair, the gray and even nearly blue eyes, and remarkably abundant beards—something which is elsewhere uncommon among Eskimos.
(Stefansson, 1908, p. 379)

Stefansson advanced four possible explanations: a) recent European intermixture with whalers or fur traders; b) ancient European intermixture with the Greenland Norse; c) ancient migration of a fair-haired Eurasian people from across the Bering Strait; and d) independent mutation. He was skeptical about the first two explanations:

… no whaler or other person familiar with it has ever suggested that any whaler came in contact with the Victoria Islanders before Captain Klinkenberg in 1905.

The only tenable hypothesis in connection with whaling is that the European blood may have come from the east side of the continent through the Americans, Scotch, and others who have engaged in Hudson Bay and Baffin Bay whaling for centuries. Here we are dealing with no impossibility any more than we were in the case of the earlier and more numerous Greenland Norsemen. But if the mixing of races is so recent, it would appear that it should be most conspicuous farther east where the whalers had their headquarters, fading away as one goes westward. The opposite is the case.
(Stefansson, 1908, pp. 377-378)

Stefansson opted for the last explanation as the most probable: “It is possible that for some so-called accidental reason blond individuals may have been born from time to time in the past from parents of pure Eskimo blood, and that these may have perpetuated themselves” (Stefansson, 1908, p. 381).

Some new light has been shed by a team of researchers headed by Palsson (2008). They collected genetic data from 299 Inuit on Victoria Island and at adjacent locations, as well as from other Inuit or Inuit-related groups (Greenland Inuit, Chukchi, Siberian Yupiit, and Alaskan Aleut). No evidence of European admixture is apparent in the Victoria Island Inuit with respect to either maternally or paternally inherited lineages. But there is evidence of maternal lineages from a pre-Inuit source, possibly the Dorset people who inhabited the Canadian Arctic a thousand years ago.

What conclusion should we draw? Palsson (2008) concluded that the existence of blondism among the Victoria Island Inuit had been blown out of all proportion. Alternately, it may be that new alleles for hair and eye color arose independently through mutation, with some kind of selection pressure favoring these color traits over the original black hair and brown eyes. Finally, it may be that a pre-Inuit population of Eurasian origin, perhaps the Dorset or even the earlier Paleoeskimos, had a significant incidence of fair hair and fair eyes. Such traits might then have persisted through admixture in this Inuit group. The last possibility might not be so far-fetched, since fair hair has been reported among the Yukaghir of eastern Siberia (von Hellwald, 1882).

References

Palsson, G. (2008). Genomic anthropology. Coming in from the cold? Current Anthropology, 49, 545-568.

Stefansson, V. (1927). My Life with the Eskimos. New York: The MacMillan Co.

von Hellwald, F. (1882). Völkerkunde, Nurnberg.

Polygyny and X-chromosome diversity

Last year, a team of University of Arizona researchers found evidence of widespread polygyny in five different human populations: Biaka (Central African Republic), Mandenka (Senegal), San (Namibia), Basques (France), Han (China), and Melanesians (Papua New Guinea). In short, the maternally inherited X chromosome was genetically more diverse than the chromosomes inherited by both sexes (autosomes) (Hammer et al., 2008). So more women than men seem to have contributed to the gene pool. Surprisingly, there was little difference in this respect between the Mandenka (known to be highly polygynous) and the Basques and the Han (among whom the incidence of polygyny is much lower).

I was frankly skeptical. For one thing, maternally inherited genetic diversity reflects not only the number of women who contribute to the gene pool but also their own genetic diversity. If these women are drawn from a larger geographic area than the men are, the female gene pool will be more genetically diverse than the male gene pool. This is often the case. In a patriarchal society, land ownership is vested in the man’s lineage, so women are usually the ones who move to their mate’s community when they get married. We see this ‘patrilocality’ even in societies where land ownership is matrilineal. Among the Iroquois, wives were often abducted from other tribes through warfare.

In any case, the above findings have now been challenged. Another study has found much less maternally inherited genetic diversity in East Asians and Europeans than in West Africans (Keinan et al., 2008).

So what gives? The methodology is similar in both studies. John Hawks points out that the second study scales X-chromosome diversity to the human-macaque divergence whereas the first study uses the human-orangutan divergence. While this might explain differences in calculation of mutation rate and hence X-chromosome diversity, I don’t see how it could explain why one study found geographic differences (i.e., African versus non-African) and the other did not.

I suspect that the key difference is that the first study just did not have enough resolution to pick out these geographic differences, i.e., its dataset was too small. The second study used 130,000 loci (SNPs) whereas the first one used 40.


Please check out my latest article: “Sexual selection and human geographic variation” in The Journal of Social, Evolutionary & Cultural Psychology.

References

Frost, P. (2008). Sexual selection and human geographic variation, Special Issue: Proceedings of the 2nd Annual Meeting of the NorthEastern Evolutionary Psychology Society. Journal of Social, Evolutionary, and Cultural Psychology, 2(4), pp. 169-191.
http://www.jsecjournal.com/articles/volume2/issue4/NEEPSfrost.pdf

Hammer, M.F., Mendez, F.L., Cox, M.P., Woerner, A.E., & Wall, J.D. (2008). Sex-biased evolutionary forces shape genomic patterns of human diversity. PLoS Genet, 4(9), e1000202. doi:10.1371/journal.pgen.1000202

Keinan, A., Mullikin, J.C., Patterson, N., & Reich, D. (2008). Accelerated genetic drift on chromosome X during the human dispersal out of Africa. Nature Genetics, early view December 2008; doi:10.1038/ng.303

Mental traits and human variation

An interesting article has come out in Edge by Jonathan Haidt, a University of Virginia psychologist and author of The Happiness Hypothesis. Essentially, he argues that science will soon embrace the idea that human nature evolved not only in the hunter-gatherer environments of the Pleistocene but also in the diverse social environments of the past 10,000 years.

Russian scientists showed in the 1990s that a strong selection pressure (picking out and breeding only the tamest fox pups in each generation) created what was — in behavior as well as body — essentially a new species in just 30 generations. That would correspond to about 750 years for humans. Humans may never have experienced such a strong selection pressure for such a long period, but they surely experienced many weaker selection pressures that lasted far longer, and for which some heritable personality traits were more adaptive than others. It stands to reason that local populations (not continent-wide "races") adapted to local circumstances by a process known as "co-evolution" in which genes and cultural elements change over time and mutually influence each other.

… No new mental modules can be created from scratch in a few millennia, but slight tweaks to existing mechanisms can happen quickly, and small genetic changes can have big behavioral effects, as with those Russian foxes. We must therefore begin looking beyond the Pleistocene and turn our attention to the Holocene era as well - the last 10,000 years. This was the period after the spread of agriculture during which the pace of genetic change sped up in response to the enormous increase in the variety of ways that humans earned their living, formed larger coalitions, fought wars, and competed for resources and mates.

… traits that led to Darwinian success in one of the many new niches and occupations of Holocene life — traits such as collectivism, clannishness, aggressiveness, docility, or the ability to delay gratification — are often seen as virtues or vices. Virtues are acquired slowly, by practice within a cultural context, but the discovery that there might be ethnically-linked genetic variations in the ease with which people can acquire specific virtues is — and this is my prediction — going to be a "game changing" scientific event.

Haidt predicts that the paradigm shift will occur as genome research uncovers evidence that many mental traits differ among human populations. These findings will be unexpected and disturbing to some. “Expectations, after all, are not based purely on current evidence; they are biased, even if only slightly, by the gut feelings of the researchers, and those gut feelings include disgust toward racism.” In making this prediction, Haidt feels some foreboding:

I believe that the "Bell Curve" wars of the 1990s, over race differences in intelligence, will seem genteel and short-lived compared to the coming arguments over ethnic differences in moralized traits. I predict that this "war" will break out between 2012 and 2017.

Predictions for 2009

Human genomics

The Neanderthal genome will be fully sequenced. There will be no evidence of interbreeding with modern humans (although proponents of the multiregional model will remain unconvinced). By comparing this genome with ours, we may reconstruct the genome of archaic humans who lived almost a million years ago and who were ancestral to Neanderthals and modern humans.

Meanwhile, work will begin on sequencing the genome of early modern humans (10,000 – 40,000 years ago). This project should ultimately prove to be more interesting by showing us how much modern humans have evolved during their relatively short existence. We will probably find out that John Hawks erred on the low side in concluding that natural selection had changed 7% of the human genome over the past 40,000 years.

Darwin remembered

With the 150th anniversary of The Origin of Species, much will appear in 2009 about Charles Darwin and his life. We already know how he came up with his theory of evolution (Darwin salted away almost everything he wrote), although a few questions remain unanswered. What would he have done if he had lived longer? What did he have in mind for future projects?

Probably not much. He had said everything he wanted to say. The Origin of Species (1859) came out of a backlog that had built up in his mind during the previous twenty years. Then came The Descent of Man (1871), which used material left out of The Origin. Finally, The Expression of the Emotions in Man and Animals (1872) was largely a spin-off of The Descent. With this trilogy completed, he had little more to say. A younger Darwin might have addressed one of the dilemmas of evolution. How do selected characteristics perpetuate themselves? What keeps them from being blended away into non-existence with each generation of sexual reproduction? Darwin might have learned about another contemporary scientist, Gregor Mendel, and together the two of them might have proposed a particulate theory of genetics—more than thirty years before later evolutionists rediscovered Mendel’s work. The field of genetics would have developed much faster and, under Darwin’s guidance, may have avoided some of its later blind alleys (e.g., mutation pressure, saltationism, etc.).

Perhaps. But Darwin was unprepared for success. He had finally got to tell the world everything he had so long held back. And the world listened. From then on, a sense of emptiness took over, as if his remaining years were little more than an epilogue.

The Crisis?

The Second Great Depression will not begin in 2009. In any case, what scares me is not the prospect of a sudden drop in the standard of living. Rather, it’s that of a gradual decline to almost half its current value. That scenario is scarier and likelier. And it’s probably already started. For the past fifteen years, median wages have stagnated despite decent economic growth. What will happen when growth stays in the 0-2% range?

Neanderthals in my sinus?

About two years ago, Gregory Cochran teased GNXP readers with a suggestion that Neanderthals might still be living among us. There was a flurry of speculation. Sasquatches? Yeti? Scottish redheads? Finally, the answer has come out. Greg thinks there may be infectious organisms that originally developed from Neanderthal tumors several tens of millennia ago. These organisms might look like amoebae, but genetically they would be Neanderthals.

The general idea is that host cell line infections can occur (TVT, Tasmanian devil facial tumor, and a contagious leukemia in Syrian hamsters), can mutate into something that is nonlethal and/or chronic if selection favors that (TVT usually goes away with time), can infect related species (TVT can be experimentally transmitted to wolves, jackals, coyotes and red foxes), and might exist in humans today. There are human diseases that appear infectious for which the transmissible agent has not been identified - sarcoidosis, for example. So modern humans might suffer from infectious organisms directly derived from Neanderthals or other archaic humans. As far as I know, no one has yet thought of looking for Neanderthal-derived cells inside people. Since such cells would have the required genetic code for making human signal molecules, they might be particularly likely to employ baroque forms of host manipulation.

… there _could_ be Neanderthal-derived cell line infections, and this is really the only scenario I've been able to come up with that gives us live Neanderthals - hiding in your sinuses, or maybe your prostate. The only one so far. There are other known infectious diseases in which some metazoan has completely chucked complexity and gone back to being a germ: whirling disease in fish, for example.

Will it then be possible to resurrect Neanderthals à la Jurassic Park? Another GNXP commenter, Eric J. Johnson, poured cold water on the idea:

… the problem would be a lack of purifying selection on all the morphogen genes, not to mention all the neuron-specific genes, etc. The tumor doesn't need any of that stuff. How fast they would all turn to garbage, I don't know. Probably pretty fast.

Gene-culture co-evolution and evolutionary psychology

How much do human populations differ from each other in real, functional terms? The question remains open, but an answer is starting to unfold. In 2007, a team led by anthropologist John Hawks found that natural selection seems to have modified at least 7% of the human genome over the last 40,000 years, i.e., during the period when modern humans spread out of Africa and peopled the other continents. In addition, as they moved into these different physical and cultural environments, the pace of genetic change seems to have speeded up, particularly after the advent of agriculture 10,000 years ago. The rate of change may then have been over a hundred times what it had been during most of human evolution (Hawks et al., 2007)

We do not fully know the nature of these recent genetic changes. John Hawks suggests they may reflect adaptations to new ecological and cultural settings, specifically to cold, to new diets (cereals, milk, etc.), to new epidemic diseases associated with the spread of agriculture (smallpox, malaria, yellow fever, typhus, cholera), and to new forms of “communication, social interactions, and creativity.”

There thus seem to have been multiple EEAs in relatively recent times, and not simply one situated in the Pleistocene. Some of them would correspond to the different physical environments that modern humans moved into as they spread out of Africa 40 to 50 thousand years. Most however, seem to have arisen in the past 10 thousand years and correspond to different cultural environments.

John Hawks is certainly not the first one to suggest that culture has been a key part of the human adaptive landscape. Usually referred to as ‘gene-culture co-evolution’, this paradigm has had many proponents, notably Pierre van den Berghe, Charles Lumsden, and E.O. Wilson. It has nonetheless remained marginal, even among evolutionary psychologists. This is partly because of the influence of John Tooby and Leda Cosmides, whose influence was critical during the early years of evolutionary psychology:

It is no more plausible to believe that whole new mental organs could evolve since the Pleistocene—i.e., over historical time—than it is to believe that whole new physical organs such as eyes would evolve over brief spans. It is easily imaginable that such things as the population mean retinal sensitivity might modestly shift over historical time, and similarly minor modifications might have been made in various psychological mechanisms. However, major and intricate changes in innately specified information-processing procedures presentover brief spans of historical time. (Tooby & Cosmides, 1989)

In a more recent article, they have backed away from this position: “Although the hominid line is thought to have originated on edges of the African savannahs, the EEA is not a particular place or time.” Each biological adaptation has its own EEA, which is simply a composite of whatever selection pressures brought it into being (Tooby & Cosmides, 2005). There are thus potentially as many EEAs as there are adaptations. It follows, then, that some EEAs may have existed later in time than others.

How much later? Tooby and Cosmides considered complexity to be one limiting factor. The more complex the adaptation, the more genes it would involve, and the longer the time needed to coordinate the evolution of all those genes. Therefore, recent biological evolution has probably only involved simple traits, certainly nothing as complex as mental ones. Such traits could have arisen only through a faster process, notably cultural evolution.

The problem with this argument is that complex traits do not arise ex nihilo. They arise through modifications, deletions, or additions to existing traits. And such changes can occur through a single point mutation at a regulatory gene. As Harpending and Cochran (2002) point out:

Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted.

Gene-culture co-evolution also presents difficulties that are inherent to the paradigm itself:

1. The linkages between genes and culture tend to be remote, indirect, multiple, and complex. There are some straightforward ones, such as between lactose intolerance and consumption of dairy products, but such linkages are probably unrepresentative of gene-culture co-evolution.

2. With only a few minor exceptions, gene-culture co-evolution is specific to humans. Cross-species comparisons, so common in other fields of evolutionary study, are thus of little help (van den Berghe & Frost, 1986).

These difficulties are not insuperable. To some degree, they reflect an unconscious desire to study human evolution with the same conceptual tools that have been used to study the evolution of other species. Other tools will have to be developed, or simply borrowed from the social sciences of psychology, sociology, and anthropology. Thus, there are no real barriers to renewed use of this paradigm, particularly as we move beyond the single-EEA model and investigate this 7% of the human genome that has apparently changed over the past 40,000 years.

References

Harpending, H. & G. Cochran. (2002). "In our genes", Proceedings of the National Academy of Sciences, 99(1), 10-12.

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, & R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA), 104, 20753-20758.

Tooby, J. & L. Cosmides. (2005). Conceptual foundations of evolutionary psychology, in: D. M. Buss (Ed.) The Handbook of Evolutionary Psychology, Hoboken, NJ: Wiley, pp. 5-67.

Tooby, J. & L. Cosmides. (1989). Evolutionary psychology and the generation of culture, Part I. Theoretical considerations, Ethology and Sociobiology, 10, 29-49.

van den Berghe, P.L., & Frost, P. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.