Tag Archives: evolution

Sex and Evolution?

I like Michael Stoddart’s books in general–he has some great contributions to make and is one of a few popular scientists promoting olfaction. While reading his most recent book, I have been a bit frustrated by the simplistic view of human evolution and behavior. A recent Guardian piece by him “Smell evolution and the sex brain: Why we’re monogamous and use perfume” captures the source of my frustration. As a biological anthropologist, I find it hard to read the following sentence:

To keep male and female together to provide protection for babies, a suite of anatomical and physiological features evolved to promote the constant availability of sex throughout the year – irrespective of the monthly ovulation cycle.

The argument is that a suite of traits evolved (e.g., reduced sexual dimorphism, hidden estrus) to render human females receptive to sex at any time and this has led to monogamy–meanwhile male receptivity to sex is used as an explanation for purported male promiscuity. Huh! The constant male bias in science is at the heart of taxonomy–our class is called mammal because male scientists felt the key trait of mammals was the use of mammary glands to feed offspring.

Increasing the diversity of voices in academia has allowed us, slowly, to move away from teleological explanations for human behavior based on western society. In biological and evolutionary anthropology, human reproduction is a hot topic and more complicated. Stoddart does qualify his statement a bit:

Yet Homo Sapiens is the only species among the 5,500 kinds of mammal to maintain monogamous family relationships – or at least serially so – and to live in densely populated areas. This combination is extremely rare in nature.

Marriage, as an institution is barely thousands of years old (our species is 200,000 years old) and the concept of marrying for love younger still. Divorce is higher today partly because there are fewer economic and political structures keeping people together–religion is what is left and that doesn’t appear strong enough for most people–divorce was central in Henry the VIII’s split with the Pope. Most cultures are polygamous even if most end up practicing monogamy (mainly due to financial and/or political constraints–not enough money or power to gain more spouses). Perhaps the clearest statement we can make on pair-bonding is that humans can, and often do, come together in a pair-bond for a period of time with a goal of child rearing but this shared interest isn’t immediately linked to sexual monogamy–they are separate issues. The period of shared interest (if it occurs) enables the child to reach a point where the ‘village’ can take on some of the burden through formal and informal education. But, even western society regularly abandons its children–part of the year, I live next door to a youth shelter and drop-in center so I see it daily.

I suppose most humans are humanists–Jon Marks is a biological anthropologist who has written many books on the subject from an evolutionary perspective with a goal to distinguish us from all the other primates. I am not a humanist even if I do appreciate what we have accomplished as a species (there’s a lot to be ashamed of too…). I think there is an inherent fallacy in not recognizing that we are animals and that we cheat and lie and love and, yes, react to odors just as animals do. We may be enculturated to curb instincts but the instincts that we are enculturated to curb and how we do so vary cross-culturally. The goal to overcome our instincts with reason is a cultural one, not a biological or evolutionary one.

And, contrary to this blanket statement:

Today we have a global fragrance market equal to the GDP of a medium-sized country. But because our nose (unlike the VNO) ultimately sends all smells for rational analysis by the brain, we do not slavishly respond to sex smells in the way dogs or mice do. An alluring perfume may help a relationship, but no perfume comes with a guarantee!

odors are first processed in the areas of the emotional center of the brain where memories are also deal with–we react to odors before the frontal lobe (where reasoning attempts to modulate instinct) gets the data and formulates a response. Maybe we wear perfume because it smells good–it takes us to places we want to be or reminds of us of memories we love or smells like things we love to eat–maybe wearing perfume is about sensuality not mating. Why is so much academic work reductionist? But, perhaps that is why I am a biological anthropologist, rather than a biologist. Still, I take the point that we may not react to odors with the full behavioral response other animals might, but we react nonetheless. The closing statement of the piece is perhaps the strangest, and to an anthropologist, the most off-putting:

And so we can live in at least relative harmony with our fellows, benefitting from the long-term genetic and evolutionary advantages provided by monogamy, while participating socially in everything society has to offer.

There probably should be more biological anthropologists writing popular press books on human evolution and this gives me even more motivation to get my long overdue book Smell of Evolution out!

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Filed under anthropology, Anthropology and Evolution, Olfaction, primate social life, religion, Science, Senses, sex

The piggy smell of Eurasian genetic landscapes

Between 6000-4000 years ago (according to study published in Nature Communications), indigenous Mesolithic hunter-gatherers acquired pigs from Neolithic farmers immigrating to Europe. I have been interested in Pleistocene pigs for a while (and their continued association with humans into the Holocene). The reason for my interest is that pigs produce a lot of androstenone (a sex steroid), especially males, and humans vary in their genotypic/phenotypic perception of androstenone.

Human variation in androstenone perception depends on two non synonymous SNPs (Keller et al. 2007), R88W and T133M. These SNPs appear to play a role in meat preference: Lunde et al. (2012) found that wild type humans (RT/RT) rated the meat of non-castrated male pigs less favorably than those with variant alleles (RT/WM and WM/WM). HapMap and 1000 Genomes are great resources but do not capture the variation local human populations, let alone the anthropological underpinnings of variation. In my lab and using a wide mix of global human populations, I found significant variation in androstenone perception frequencies, with higher frequencies of mutations throughout Eurasia–an area heavily invested in pig meat throughout human prehistory; in Japanese and Northern Europeans, the frequency of homozygote recessive mutations is much higher and these areas have a rich history with pigs–especially Japan.

Currently, I am working through the archaeological data for human-pig interaction in Europe and Asia (with a special focus on Asia as the origin of all pigs–see here and here for starting places) to interpret the results of the genetic data. Both the archaeological data and genetic data are thin when taken across such a huge space but they are a starting point; a neat study would be to find a locale with a rich archaeological record, human population to test for the gene and perception, and a good ethnohistory on the relationship with pigs–something I am working on right now.

Combining data from the archaeological record and the genetic history of human populations adds depth to what could, on their own, be interesting but uncontextual datasets. Taken together, these datasets can paint a more detailed picture of the evolutionary inter-relationship between genes and diet.

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Filed under Analysis, anthropology, Anthropology and Evolution, Food, Olfaction, Senses

Evolution, Emotion, and Language

In a study on Meerkats in the Kalahari Desert, a team from the University of Zurich found that young meerkats respond to vocalization information about “threat urgency” (via tone) earlier than “threat type” (via variation in vocalization) as compared to older meerkats who can distinguish both pieces of information. The researchers argue this association between tone and urgency/emotion is hard-wired. This interests me because primate vocalizations have been studied extensively. For instance, the ververt monkey has eight different vocalizations for threat, each one referring to a different type of predator (such as chattering teeth for a snake). If the findings of the meerkat are observed in additional species, detection of emotion (as they interpret urgency in utterance) might indicate an evolutionarily conserved trait.

In a seemingly unrelated article from Scientific American, linguists at the University of Edinburgh have found a link between two genes (ASPN and microcephalin) involved in brain development and language in a study of 49 different populations. (The original study was published in PNAS this week.) The genes studied are active during embryonic brain development (influencing brain size). Developmentally, they may also serve a function in brain structure. Previous research has found no relationship between popular mutations of these genes and intelligence, social ability, and brain size. They appear to affect the cerebral cortex (which plays a role in understanding language). Researchers tested for a relationship between many genes and many aspects of language. They found a positive relationship between these mutations and language tone. Most languages fall into one of two categories (tonal or non-tonal). Exceptions include Japanese, some Scandanavian dialects, and Basque. Tonal languages are ones where the pitch of the spoken word makes a difference in meaning. Nontonal languages are ones where the pitch does not make a difference in meaning. The mutations date to about 37,000 years ago and are found in abundance in nontonal language speakers. Tonal language speakers do not have these mutations.

A note of caution in interpreting these findings from the article:

Northwestern’s Wong says that in a field in which researchers struggle to determine whether differences arise from experience or genetics, the new study “gives us an idea that there is a genetic side to things.” He says the research indicates that small differences in brain organization determined by genetic makeup may be amplified by cultural factors and contact with other languages through war or migration, creating today’s dichotomy in language tonality.

“Even remarkable correlations can arise by coincidence—or, in this case, possibly by prehistoric migration factors that are currently unknown to anthropology and archaeology—so we can’t rule that out,” Ladd says. “The next step is to attempt to correlate individual genotypes with measurably different behaviors on experimental tasks that are plausibly related to language and speech.”

The latter study has many components that require further study but the initial findings are interesting especially in light of the meerkat findings. This developmentally early comprehension of tone is likely to be evolutionarily conserved in mammals (dating back to a mammalian common ancestor and not lost in the majority of subsequent species derivations). So, if we accept the findings of the linguistic study for heuristic purposes, tonal languages would be ancestral to nontonal languages since nontonal languages are associated with a recent mutation and tonal language speakers lack it. But, this is counterintuitive to the meerkat study (that already has a strong base of supportive research). Why? If tone is evolutionarily conserved because it is associated with fitness, or net reproductive success (here, survival via an ability to perceive urgency of threat and, thus, escape predation), then alterations to the meaning of tone would interfere with its function as a vehicle for emotion, urgency. Tonal languages innovate a new use for tone. Rather than urgency, tone now conveys a difference in meaning. But, with what little linguistic knowledge I have, the tonal languages that I am aware of are older than nontonal one (ex. Chinese is tonal and English is not).

I know I am linking the findings of two unrelated studies. But, so much of what occurs in the science research today lacks context within and across disciplines. By lack of context, I mean a failure to contemplate evolutionary meaningfulness. I expect case studies in smaller specialized journals to disseminate current research findings to the discipline but in a larger journal like PNAS, I expect more context.

So, that said, I wonder if this finding, after further exploration and testing, will actually be supported as a valid relationship (e.g., one that has meaning as opposed to one that is coincidental). At the very least, it presents interesting data to those interested in this growing gene-culture approach to prehistory (with language representing genes) and population migrations.

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