There may be no gene which is essential for our humanity

By Razib Khan | October 11, 2012 12:39 am

The always informative Ann Gibbons has a piece in Slate, The Neanderthal in My Family Tree. There is almost nothing new for regular readers of this weblog, but it’s rather awesome that Slate is now publishing stuff like this. Many people are simply unaware of the new paleogenomics. Case in point, a good friend who has a doctorate in chemical physics, and was totally unaware a year after the seminal Science paper on Neandertal admixture of the likelihood of Neandertal admixture!

Nevertheless, I think it is important for me to be repetitive and highlight a disagreement I have with the Gibbons’ piece. She says:

…But the differences in the genomes of Denisovans, Neanderthals, and modern humans are also revealing the genetic traits that set us apart from them—the traits that made us human. “I’ve been comparing it to the pictures of Earth that came back from Apollo 8. The Neanderthal genome gives us a picture of ourselves, from the outside looking in,” says paleoanthropologist John Hawks of the University of Wisconsin in Madison, in his blog on paleoanthropology, genetics, and evolution. “We can see, and now learn about, the essential genetic changes that make us human—the things that made our emergence as a global species possible.”

This line of thinking is not Gibbons’ creation. Svante Paabo himself is promoting it. And obviously it’s not crazy. We can learn a lot from comparative genomics. But I want to reiterate that there may be no essential or necessary genetic change in the hominin lineage which led to modern humanity. I’m not saying that this is a done deal. Rather, we need to move toward a position of more agnosticism as to how humans came about. As humans we think we’re very special, so there must have been very special genes which gave rise to our very special traits. This need not be so. Humility is warranted at this point, in light of the major revisions in our understanding of the past due to paleogenomics.

As analogy, consider someone who is very tall. Is there an essential genetic change which confers upon them tallness? No. Height seems to be controlled by innumerable variants of small effect, and it is the sum totality of these changes which results in extreme values of height. And importantly different genetic configurations can lead toward the same trait value. Similarly, human encephalization and facility with cultural production may also be due to small but continuous changes on a range of loci. There may have been no specific change which led to humanity.

This is all important because I think there’s a non-trivial probability that in the near future someone will publish a paper which claims to have found the Allele Which Made Us Human. More realistically, that will be the press release spin, even if the paper is more judicious. We need to be cautious and be on guard against this. There may be many alleles which differentiate Neandertals & Denisovans from modern humans, but that doesn’t mean that those alleles are responsible for our differences. If we presuppose a model the genomic evidence is such that we may swallow up false positives wholeheartedly.

Please do note that I am not forwarding an unequivocal position. I don’t know if there was a point mutation which made humanity, or if humanity is a continuous and quantitative trait. Rather, I think we need to be more careful about the inferences we make because of the robustness of our background assumptions. We’re special, and we know. But that doesn’t mean that we can let that intrude in the judgments of science.

CATEGORIZED UNDER: Anthroplogy, Human Evolution
MORE ABOUT: Human Evolution
  • gcochran

    Probably no single allele is sufficient, but some may be necessary.

  • http://neuroskeptic.blogspot.com Neuroskeptic

    Good point. And I can see this being extremely divisive, because supposing someone does propose the “Human Gene”, it is very likely that there will be people who lack that gene. Suppose the “Human Gene” is a neurodevelopmental gene, which seems logical, well, most mutations in those genes cause developmental delay / mental retardation / whatever you want to call it, so it is very likely that some people with such disabilities will be classed as “non-human” if such a gene is claimed.

    And that will lead to fireworks.

  • http://delicious.com/robertford Darkseid

    PBS is running their “What Makes Us Human” shows lately. They made up someone to look like a Neandertal might have looked and then had him walk in public to see if people would notice. It was a pretty good overview…

  • Gollux

    It seems obvious that looking for the gene that makes us human is like looking for the dollar that makes Warren Buffett rich.

  • Charles Nydorf

    I vividly remember that when my grandmother hadn’t had a chance to see a newspaper for a few days, she would announce dramatically “I am living like a wild beast!” I think she meant that although we are genetically human, it is largely elaborate social and cultural conditions that make us live differently from other animals.

  • Superfast Jellyfish

    I’ve brought up the possible non-binariness of humanity with my very religious wife and it makes her uncomfortable. The unarticulated assumption seems to be that at some discrete point in pre-history we all of a sudden went from no humans to lots of humans, so presumably there was some generation way back when where the parents lacked souls but the children had them.

  • http://www.thesubversivearchaeologist.com Rob Gargett

    Dead on. I think it’s worth adding that the recent claim from Svante Pääbo’s team–dating of the most recent … er … interaction between the Neanderthals and our lineage–allows for the possibility that it took place when the two were at more or less the same point of cognitive evolution–neither being modern human. Both exhibited a technology known as the Mousterian, and left behind other archaeological traces of a comparable nature, which many would agree is a very different archaeological record than that associated with what we call modern humans, since about 40,000 years ago. Thus, ‘we’ could well have interbred with the Neanderthals while still, if you will, their evolutionary equals. The existence of the skeletally modern form at Qafzeh Cave, Israel, at about 100,000 years ago and that of Neanderthals at 60,000 from Kebara Cave, just ‘down the road’ from Qafzeh, is evidence that the interbreeding could well have taken place during the 40,000 years in between. In this scenario modern humanity arose later in the skeletally modern, essentially African, morphospecies, after the interbreeding had taken place. The work to which I’m referring can be found here: http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1002947. [I’m hoping my early morning A-game is up to the standard that you consistently demonstrate in your writing.]

  • Chad

    Our common notion of “species” is fundamentally flawed. Of course Biologists have always struggled at some level to define it, but I think those problems are rearing their head with far greater force as more genomes are being sequenced allowing for unprecedented comparisons and insight.

    In plants a lot of very well studied and economically important species are hybrids in the most extreme sense. Cabbage, Broccoli, or grains like Triticale, are in fact allopolyploids. Its apparent that these hybridizations have been important in the evolution of many plant species. Which flies in the face of our common understanding of “species”.

    I wonder how much a barrier thinking in terms of “species” is to making real progress in understanding the evolution of humans and life?

  • jose

    I have a question. My understanding (and I could be totally wrong) was that the neanderthal DNA was entirely from male neanderthals and not females.

    My assumption is that this is likely due to male neanderthals raping female humans. Is that a valid assumption?

    The image in my head is of early human tribes venturing into neanderthal habitats and occasionally a female human getting raped by a neanderthal male while she is out gathering food or something. Or perhaps a neanderthal male snuck into the camp. And then 9 months later she gives birth to a somewhat odd looking hybrid baby, but the human tribe accepts the child.

    Is that a reasonable model? Is rape by neanderthal males the likely source of the neanderthal DNA? Is there any chance human females sought out neanderthal males to mate with? A Romeo and Juliet situation, perhaps? Or just a human and neanderthal tribe that, for a time, shared the same water source.

    I was just curious if I was way in left field by assuming it was likely rape by the neanderthal males that caused the admixture. Thanks.

  • Sandgroper

    #9 – No way of knowing, and futile to speculate, in the absence of evidence of something like mixed cohabitation.

    But I do get ever so sick of seeing stupid references to ‘trysts’ etc. as if whatever mating took place necessarily involved ‘lurve’.

    If within-group mating among at least some anatomically modern human hunter gatherers did not involve any concept of ‘romance’ or ‘choice’, why on earth should anyone assume it did between Neanderthals and AMHs? At least one possibility, which has been recorded among some modern hunter-gatherer groups, is abduction and group rape of females. Not too romantic.

    But what does it matter? The genetic interest is surely in that it happened, not particularly in how – that doesn’t require very much imagination.

    The wrongness in seeing ourselves as uniquely human and Neanderthals and other extinct lineages as something other than ‘us’ as uniquely human just seems like a dumb perpetuation of something that current knowledge should have dispelled by now.

  • Chad

    “All organisms and organic phenomena are composed of unique features and can be described collectively only in statistical terms. Individuals, or any kind of organic entities, form populations of which we can determine the arithmetic mean and the statistics of variation. Averages are merely statistical abstractions, only the individuals of which the populations are composed have reality.”

    -Mayr

  • Sandgroper

    #11 – I just clicked the non-existent ‘like’ button.

  • skid

    If I had to pick one gene, I’d pick the foxp2 gene, but then again, Neanderthals and Denisovans apparently carried that gene as well.

  • AG

    It is very likely that human does not have many specific genes unique. Genetic architecture in which how genes interact and sequentially express is very likely answer to major difference in different species. The same building bricks can be used to create numerous different buildings.

    Just speculation or opinion. No data here

  • Justin Giancola

    yo sandgrope, can you point me to some sources that give credence to what you talkin bout?! :o

  • Sandgroper

    Which part? >:(

  • Justin Giancola

    bout the tribal gang rape :(

  • ruth

    To frame the question like Gibbons and Pääbo do (“What makes us human”) is idiotic. Clearly, most of what distinguishes “humans” from our ape relatives was already present in Neandertals and other late archaics in the homo family. They were all “human”.
    The idea that a further sea change in mental capacity occured between them and us is nothing but a hypothesis so far, with scant evidence in its favor. Cultural/technological differences between Neandertals and their modern contemporaries, as far as they are visible from the archaological record, are tiny, inconclusive and certainly smaller than differences between, say, 19th-century and 21-century moderns, or synchronous differences between moderns in countries with different levels of development. Children whose grandparents were illiterate subsistence farmers in India, with an average IQ of 81 if you believe Lynn, excel in the British school system. They haven’t suddenly changed genetically (though epigenetically there might well be changes).
    I’ not saying we are not mentally special compared with Neandertals (it may turn out that we are). It’s just that at the moment we really have no hard evidence for this convenient self-congratulatory hypothesis.

  • Prof.Pedant

    I’ve suspected for awhile that there were no uniquely human genes, and I anticipate that if we ever become able to construct viable genomes from individual genes that someone will eventually construct a completely human genome out of genes from non-human sources.

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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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