The evolution of the human face

By Razib Khan | March 26, 2012 12:58 pm

The face is an important aspect of our phenotype. So important that facial recognition is one of many innate reflexive cognitive competencies. By this, I mean that you can recognize a face in a gestalt manner, just like you can recognize a set of three marbles. You don’t have to think about it in a step-by-step fashion. Particular types of brain injuries can actually result in disablement of this faculty, and a minority of humans seem to lack it altogether at birth (prosopagnosia). That’s why I’ve long been interested in the genetic architecture and evolution of craniofacial traits. I long ago knew the potential range of pigmentation phenotypes for my daughter because both her parents have been genotyped, but when it comes to facial features we’re stuck with the old ‘blending inheritance’ heuristic. The most obvious importance of teasing apart the genetic architecture of craniofacial traits is forensics. It might not put the sketch artist out of a job, but it would be an excellent supplement to problematic eye witness reports.

But it isn’t just forensics. The issue has evolutionary relevance. It looks like that in terms of morphology our own lineage has had a lot of diversity up until recently. I’m thinking in particular of the ‘archaic’ looking humans recently discovered in China and Nigeria, who seem to have persisted down into the Holocene. More generally, humans as a whole have become more gracile over the last 10,000 years. Why? There are two extreme answers we can look to. First, gracile humans have replaced robust humans. Second, natural selection for gracility has resulted in the in situ evolution of many populations over the last ~10,000 years. An interesting aspect of this is that it looks as if many salient traits have been targets of selection, and therefore evolution and population differentiation.

Here the top 10 SNPs which deviate from the overall phylogenetic tree of population relationships in the HGDP data set:

 

SNP Chr Nearest gene Phenotype
rs1834640 15 SLC24A5 skin pigmentation
rs260690 2 EDAR hair morphology
rs10882168 10 CYP26A1/FER1L3 ?
rs4918664 10 CYP26A1/FER1L3 ?
rs2250072 15 SLC24A5 skin pigmentation
rs6583859 10 CYP26A1/FER1L3 ?
rs2384319 2 KIF3C ?
rs6500380 16 LONP2 ?
rs4497887 2 CNTNAP5 ?
rs9809818 3 FOXP1 ?

There are two things I want to say off the bat. First, a given SNP likely has many phenotypic effects. So the trait that we “see” in terms of its effect may not be the same trait that natural selection “sees.” Second, it is not a surprise that out of the traits that a given variant may affect the physically salient ones stand out; sometimes you do go looking where the light is shining on a dark street. We know that the lighter complexion of East and West Eurasians seems to be due to independent evolutionary events. In other words, they aren’t derived from common ancestry. When it comes to hair form the EDAR locus seems to be responsible for the distinctive characteristics of East Asians, and has been under recent selection.

What does all this have to do with craniofacial traits? Simple: the coarse and “skin deep” traits that physical anthropologists used decades ago to classify human beings have been rather informative to a first approximation of both details of phylogeny and natural selection. I see no reason why craniofacial traits should be any different. Humans have become more gracile, and some human populations seem to have been changing rather rapidly. I am highly skeptical that this is a neutral process. We care a great deal about facial features, and deviation from the norm can be arresting. If there has been change it is either due to population replacement, or selection (it could be a correlated response, or direct selection).

It is with that preamble that I offer up Mark Shriver’s abstract at the Modern Human Genetic Variation symposium:

The genes determining normal-range variation in human faces are arguably some of the most intrinsically interesting and fastest evolving. However, so far, little work has been focused on discovering these genes. Working under the hypothesis that genes causing Mendelian craniofacial dysmorphologies also may be important in determining normal-range facial-feature variation, and that those genes associated with population differences in facial features should have experienced greater levels of evolution (change in allele frequency), we have taken an admixture mapping/selection scan approach to identifying and studying the genes directly affecting facial features. We have applied the methods of automated quasi-landmark analyses, partial least squares regression, and individual genomic ancestry estimates to explore the distribution of facial features across two groups of human populations — West Africans and Europeans. Using three samples of admixed subjects (American; N=159, Brazilian; N=197, and Cape Verdean; N=248) we have modeled facial variation in the parental populations and compared the extent to which estimates of ancestry from the face compare to genomic-ancestry estimates. We also have tested six selection-nominated craniofacial candidate genes for functional effects on facial features using admixture mapping. In objective tests, two of these six genes (FGFR1 and TRPS1) show significant effects on facial features. In addition, human-observer ratings of the similarity between subjects and allele-specific facial morphs show the same effects for these two genes. Additionally, exaggerated allele-specific morphs based on normal-range variation in these genes recapitulates the syndromic facies of the craniofacial dysmorphologies with which they are associated.

I asked Mark about the nature of these genes and the traits. The paper is coming soon, but he told me that he does not think that the genetic architecture of craniofacial traits is going be as simple or easy to characterize as pigmentation genes. On the other hand, he’s reportedly capturing 35% of the African vs. European difference with his marker set, so that’s not trivial, and some of the individual loci have a strong enough effect that it’s visible by eye! Also, given the preserved extant diversity within populations (pigmentation genes are often disjoint across Africans and Europeans) he believes that the selection events are recent.

  • Curious

    I just finished reading The Evolution of the Human Head http://www.amazon.com/Evolution-Human-Head-Daniel-Lieberman/dp/0674046366 by Daniel Lieberman, Professor of Human Evolutionary Biology at Harvard and on of the main points he makes is that the head of vertebrates is such a complex system of interrelated features that selection for a particular phenotypic feature can cause secondary changes in others.

    In Homo Erectus he posits that the drier climate of the Pleistocene during which H. Erectus evolved an extra 100cc of cranial capacity per 500,000 years was a result of continued selection for less robust molars and jaw muscles for masticating rough fibrous tubers due to and increase in the percentage of meat in the human diet following the proliferation grasslands and large fauna which grazed upon it.

    In H. Sapiens this became even more pronounced and the decrease in bone mass necessary for ligament and tendon attachment in the skull resulted in a significant increase in cranial capacity of the brains temporal lobes and a lowering and flattening of the face in the skull which may have provided for a more articulate larynx and voice box facilitating more sophisticated patterns of speech.

    He believes there has been considerable further ongoing selection in this direction even unto the present day that can be seen in a more gracile shape of the human skull between more archaic forms of (such as early “Cro-Magnon” examples and humans fossils from 10,000 years before the present.)

    This trend in changed skull morphology has continued even more rapidly since the development of agriculture and even softer cooked foods. The size of the brain has also been reduced slightly from 150,000 years ago. Perhaps field hands require less cleverness than hunter gatherers.

  • Bahr Kaniz

    In case you haven’t seen these:

    Bad to the bone: facial structure predicts unethical behaviour (2012)

    MHC-heterozygosity and human facial attractiveness (2005)

    The second one might explain why some nerd girls can be almost disturbingly pretty.

  • http://wulfkurtoglu.blogspot.com/ Wulf Kurtoglu

    Is my crude, uninformed view on this completely wrong? I’d have said that ugly women are the price you pay for robust men, and feminised men are the price you pay for pretty women.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #3, probably mutational load. the sexual antagonistic dynamic is probably there, but is secondary.

  • pconroy

    In case anyone is interested in comparing their results for these 10 SNP’s, here are mine – I’m Irish. My parents results are almost identical to mine, except one result for my Father. My daughter is 1/2 Irish, 1/2 (Corsican, Swiss-Italian, Breton and French), while my wife is 1/2 Sicilian, 1/2 (Prussian, Polish, German)

    rs1834640 AA – SLC24A5
    rs260690 AA (Wife AC) – EDAR
    rs10882168 GG (Wife AG)
    rs4918664 AA (Wife AG)
    rs2250072 AA – SLC24A5
    rs6583859 AA (Wife AG)
    rs2384319 TT (Father GT)
    rs6500380 GG (Daughter AG)
    rs4497887 CC (Daughter CT)
    rs9809818 AA (Wife AC)

    Note: All my results are homozygous!

  • Eron

    The selection pressure on facial features may have been in part due to murder of different-looking individuals. There is some historical evidence, for example, about the IV century Chinese civil war:

    “Shi Min saw that, in particular, the Xiongnu and the Jie would never support him, so he issued an order that if a Han killed a non-Han and presented the head, he would be rewarded. Some 200,000 died in the massacre — including some Han who had higher nose structure or thicker beard, both considered signs of non-Hanness.”

    I understand that it had something to do with memories of northern invasions in the previous century. Of course, the more recent genocide events can also be viewed this way. In general, people looking even a bit like “the enemy” must have had it difficult. This must have accentuated and perpetuated geographical differences in facial features.

    I guess there could have been a hyper-correction mechanism driving the population “common” looks away from the way “the enemy” population looked. I mean, it paid to look very different from “the enemy”. What do you think?

    In any case, it is impossible to believe any change in facial features could have been “neutral”. Even these days people get murderous about it.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    The selection pressure on facial features may have been in part due to murder of different-looking individuals. There is some historical evidence, for example, about the IV century Chinese civil war:

    what the fuck? and that’s how lactose tolerance emerged too! you murdered people with bad gas after drinking raw milk.

  • immu

    facial features have been found to be overwhelmingly the most important feature in mate selection in both sexes. We cannot understand face without sex. It is like speaking about legs without mentioning walking.

    It is not the killing of different-looking individuals, its is more subtle. People have been shown to trust a person more if they are similar-looking.

  • Eron

    Thank you, Razib, for the kind and informative answer. I take it you do not think genocide and routine murder of different-looking neighbors was an important factor. Interesting.

    And no, I do not think that about the lactose tolerance.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #8, citation? i have no idea who the hell you are and why i should listen to you (and i’m channeling my friends who prefer a tight body over a pretty face i forced to choose).

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    I take it you do not think genocide and routine murder of different-looking neighbors was an important factor

    1) neighbors usually looked the same. 2) i accept the reality that violence was rather common the past. i am skeptical that phenotypically biased violence was such a large proportion to drive these selection coefficients. 3) your argument is so skeletal and thin that it’s not easy to engage. 4) if you were awesome erudite and i respected your intellect i might take you at your word, but i have no idea who the hell you are, and certainly don’t trust your opinion as i have no information to trust your opinion.

  • immu

    Don’t be hostile! :)

    It is pretty well known fact that for some reason, face is very important. You cannot be surprised (or even offended?) by that.

    Succesful men: good face, nice voice, high sosiosexuality. Succesful women: good face.

    http://onlinelibrary.wiley.com/doi/10.1002/per.768/abstract

    “Abstract: We studied initial and long-term outcomes of speed-dating over a period of 1 year in a community sample involving 382 participants aged 18–54 years. They were followed from their initial choices of dating partners up to later mating (sexual intercourse) and relating (romantic relationship). Using Social Relations Model analyses, we examined evolutionarily informed hypotheses on both individual and dyadic effects of participants’ physical
    characteristics, personality, education and income on their dating, mating and relating. Both men and women based their choices mainly on the dating partners’ physical attractiveness, and women additionally on men’s sociosexuality, openness to experience, shyness, education and income. Choosiness increased with age in men, decreased with age in women and was positively related to popularity among the other sex, but mainly for men. Partner similarity had only weak effects on dating success. The chance for mating with a speed-dating partner was 6%, and was increased by
    men’s short-term mating interest; the chance for relating was 4%, and was increased by women’s long-term mating interest.”

  • Eron

    #11 Thank you. I am just a guy, my field of expertise is far from genetics, you absolutely do not have to trust my opinion. My question was not based on “my opinion” but on a fact. I do not remember the book I took the Chinese citation from, but the fact is well known, here is Wiki, for example:

    http://en.wikipedia.org/wiki/Ran_Min#During_the_confusion_after_Shi_Hu.27s_death

    Also, many modern instances of genocide involve killing different-looking people. Evidently, killing the different is part of human nature. (I think it can be ancient, from the times of contact with archaic humans, but I have nothing to support this guess.)

    I asked whether you think this was important enough to contribute significantly to the evolution of our facial features. You said no. Cool.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    It is pretty well known fact that for some reason, face is very important. You cannot be surprised (or even offended?) by that.

    you didn’t say very important. you said: “overwhelmingly the most important feature in mate selection in both sexes.” as for the citation, i appreciate it. though i would caution about over generalizing. they admit that it isn’t totally varied (e.g., education), as well as the fact that people who enter into speed dating are somewhat selection biased.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #13, your problem is one of quantity, not quality. a much better case would have been the mass killings of ‘westerners’ in the late 9th century in china. but the mixture of very phenotypically different populations regularly is a somewhat new feature of human existence.

  • immu

    What comes to anecdotes, even some people representing ‘superficial professions’ (night club owner, life style magazine journalist) estimated face constitutes 50 % to 77 % of total physical attractiveness. If you exclude physical attractiveness from mate selection, then you cannot say face is the overwhelmingly most important feature in mate selection.

    Actually, the researchers in the article in cited write “physical attractiveness” when they mean “facial attractiveness”. In fact, in many languages, “looking good” or “handsome man” or “beauty” means more or less “handsome/beautiful face”.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #16, i accept the importance of the face. i am simply curious about greater precision and specificity (e.g., r-squared of mating success predicted by facial symmetry). that is all.

  • immu

    Ok…! :)

  • Eron

    #15 …the mixture of very phenotypically different populations regularly is a somewhat new feature of human existence.

    How about the (up to 12000 year-long) coexistence of H. Sapiens and Neanderthals in Europe? And if the recent findings of the ‘archaic’ looking humans you mention above are correct, and all this talk about “deep population substructure in Africa”, and perhaps other findings, then we do not even have to go back 30,000 years back for it. And what about the Neolithic expansion into Europe from your previous post? Of course, long-range migrations and contact between different-looking people were common whenever one looks, not exceptions. Er, this is just an uninformed opinion, I am not pretending to argue with you on the same level. If your contr-argument is about “quantity, not quality”, I have nothing to argue with.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #19, there are two issues. spatial and temporal. first, the huge difference/mixing would occur on the frontier. not across the whole range. though granted population expansion is occurring on the frontier. but second, these expansions are still generally unlikely transients. the final issue is that the primary focus of this past is actually on natural selection within populations. so you are proposing that contact between two different looking populations results in sharper differentiation between them by selection within each population. it’s theoretically possible, but seems unwieldy to me. there are easy ways this happens with culture.

  • Matt

    I just finished reading The Evolution of the Human Head http://www.amazon.com/Evolution-Human-Head-Daniel-Lieberman/dp/0674046366 by Daniel Lieberman, Professor of Human Evolutionary Biology at Harvard and on of the main points he makes is that the head of vertebrates is such a complex system of interrelated features that selection for a particular phenotypic feature can cause secondary changes in others.

    Yeah. Not much to add here, but one of the interesting things I found about this book, on this point, was that it made clear to me what I found surprising (but in retrospect maybe not), which was that bony tissues in the head form in response to soft tissue changes – .e.g the cranial vault largely doesn’t have some determined shape or size, but is determined by brain growth and shape, interacting with the face through the cranial base and the bony face shape is formed in response to soft tissue expansion there (muscles, eyes, &c.).

    That kind of indicates that many of the gene changes for facial shape changes we find might be genes active in soft tissues (which cause the bone to model differently in response), rather than in genes directly regulating bones.

  • Miley Cyrax

    @10
    Well Razib, back in the day there was less… diversity in female rotundness… so facial attractiveness, by default, explains a greater amount of variation in male mate preferences.

    A preference for tight bodies isn’t that meaningful when every girl’s tight-bodied ;-)

  • Jon Baldur

    One question that might be connected to the rapid evelution of the face; I have three children two of which needed braces, both I and my wife are of a very isolated stock of scandinavians; the Icelanders. So many of us as well as so many Europeans seem to have too many teeth, or their teeth simply toolarge for their jaws. (My wife actually has a pair of teeth less than normal for humans.) I sometimes wonder what could be the reason for this mismatch. You are probably hard set to find such a high percetage of individuals of any species with “croocked teeth. I actually tease my children by telling them that they have the teeth of Neaderthals in a “H. sapience” jaw, this is of course meant to be a joke, but is there a know explanation for this?

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    Well Razib, back in the day there was less… diversity in female rotundness… so facial attractiveness, by default, explains a greater amount of variation in male mate preferences.

    that’s the kind of thing i was talking about. what you prefer depends on the context of the distribution of traits….

  • pconroy

    @23,
    You and your wife are in good company. All my family have the same problem, too many large teeth for a jaw front that’s too narrow – so overcrowding and crooked teeth abound. Everyone has needed braces on their teeth.

    I’ve had 4 secondary teeth removed from the front of my mouth, and still have crooked teeth. I’ve also had to have all my baby teeth removed by a dentist, as none fell out by themselves. My father even had a baby tooth removed at 70 yo.

    Here in New York some years ago, I went to an upscale dentist in Manhattan and he had to do a jaw X-Ray, before a root canal. When he viewed the negative, he said, “I’ve never seen anything like this!” He then went on to say that my teeth had much deeper roots than normal and the roots were much thicker, also the enamel on my teeth seemed to be thicker.

    My wife on the other hand has more Central European type teeth, they are small, and due to Sicilian ancestry is slightly prognathic, so more room in the front of her jaw, and so she ends up with small spaces between all teeth. She’s also is missing all wisdom teeth – they weren’t removed, she just doesn’t have any.

    My eldest has the same very deep roots and large teeth, and is having them pulled. My son’s teeth are perfect, but my 1 yo has small and crooked teeth, with gaps between them – yikes!

  • Eric

    These two articles may interest you.

    1. New research from the University suggests that many of the common orthodontic problems experienced by people in industrialised nations is due to their soft modern diet causing the jaw to grow too short and small relative to the size of their teeth. The research, which was conducted by Dr Noreen von Cramon-Taubadel from the University’s School of Anthropology and Conservation.

    http://www.physorg.com/news/2012-03-jaw-dietary-differences-human-populations.html

    Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies’ is published in Proceedings of the National Academy of Sciences.

    2. A twin study by collaborators at MIT and in Beijing, China shows that face recognition is heritable, and that it is inherited separately from general intelligence or IQ.

    “Our study provides the first evidence supporting the modularity hypothesis from a genetic perspective,” said lead author Jia Liu, Professor of Cognitive Neuroscience at Beijing Normal University in China of the study published in the January 7 issue of Current Biology. “That is, some cognitive abilities, like face recognition, are shaped by specialist genes rather than generalist genes.”

    http://www.physorg.com/news183145169.html

  • van Rooinek

    One question that might be connected to the rapid evelution of the face; I have three children two of which needed braces, both I and my wife are of a very isolated stock of scandinavians; the Icelanders. … my children by telling them that they have the teeth of Neaderthals in a “H. sapience” jaw, this is of course meant to be a joke, but is there a know explanation for this

    Insufficent nutrients — especially Vitamin D — prenatally. Proven in the 1930s. Try eating your ancestor’s diet, and have some more children, and you’ll see that the “primitive” structures will reappear. My 3rd son has perfect teeth/jaw/etc due to dietary improvments made after sons 1 and 2. read more here:
    http://www.westonaprice.org/traditional-diets/ancient-dietary-wisdom

  • pconroy

    @26 Eric,
    Interesting, I grew up picking and eating a lot of Hazel nuts – in the summer/fall period – and would crack them with my teeth. In fact I cracked all nuts with my teeth, and have very strong jaws as a result, however it didn’t help the overcrowding…

  • pconroy

    @27 van Rooinek,
    I was born with Rickets (Vitamin D deficiency), so that might explain some tooth problems I guess?

  • Tomasz R

    @Eric @pconroy

    Whole set of facial pictures of natives, that ate traditional diets vs. those on western ones can be found in Weston A. Price book “Nutrition and Physical degeneration”

    http://journeytoforever.org/farm_library/price/pricetoc.html

    It’s related to availability of vitamins K2, D, A.

    There’s even a orthodontal procedure inspired by this research that simly expands the jaw.

    http://ryan-koch.blogspot.com/2010/03/adult-palate-expansion.html

  • Jon Baldur

    @27. This will not explayn it. as we have the “old fashion ” cod liver oil at all times in the fridge, and the kids are raised with a spoonful every morning. And we are still eating fish more often than most other europeans at least. I seiously dobt that this has any bearing in our case, or Icelandic cases on the whole.

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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