Every now and then I’m asked about the ‘aquatic ape hypothesis’. My standard response is that there’s nothing to see, and everyone should just move on. But reading a new (open access) paper in Nature, Great ape genetic diversity and population history, it crossed my mind again. The reason is this section of the legend of figure 1, “The Sanaga River forms a natural boundary between Nigeria–Cameroon and central chimpanzee populations whereas the Congo River separates the bonobo population from the central and eastern chimpanzees.” I knew of the latter division. The former was novel to me. In fact I’d never even heard of the Sanaga river prior to this paper. Though the Congo seems clearly a significant geological and hydrological entity, I’m not quite so sure of the Sanaga. The division between the chimpanzees of Nigeria-Cameroon and those of the western Congo region may be one with an overdetermined number of causes. Nevertheless, taking these riverine features as a given parameters in generating allopatric speciation and subspecies level differences, I am struck by the contrast between ourselves and our cousins. In particular, the phylogeny above seems to imply that bonobos and common chimpanzees diverged on the order of ~2 million years ago, while the Nigeria-Cameroon population separated from the western Congo population ~500,000 years before the present (depending on the method of inference you rely on, though the qualitative insight here is preserved even if you switch them around). Though it took H. sapiens sapiens to break out of the world island of Afro-Eurasia, even our erectine cousins pushed on toward the southeastern extremities of Eurasia over 1 million years ago. It seems then that our savanna ape lineage is characterized by the behavior of wander lust and lack of fear of water.

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The Y chromosome is strange. It’s gene poor and loaded with repeats. That’s one reason mtDNA phylogenetic and phylogeographic analysis preceded the Y chromosome by about 10-15 years (the other major reason in the pre-PCR age is that mtDNA is very copious). While the hypervariable region of mtDNA is an excellent molecular clock because of its high mutation rate (though at a deep enough time depth this causes problems, as bases start to turnover), in the pre-next generation sequencing era hunting around the Y chromosomes for SNPs was tedious (a significant portion of Spencer Wells’ Journey of Man focused on the nitty gritty of extraction and preparation).

Despite all this one of the weirder stories over the past decade in relation to the Y chromosome is the peculiar theory promoted by Oxford geneticist Bryan Sykes, and outlined in his book Adam’s Curse: A Future without Men. As I observed above the Y chromosome has a tendency to be filled up with genetic garbage (since it does not recombine deleterious mutations tend to accumulate). There are a few important functional regions (e.g., SRY), but there’s also a reason that sex-linked diseases occur: in most cases males have to rely on the X chromosome to pick up the slack for the Y. Extrapolating this genetic decay Sykes posited that human males would disappear within ~10 million years due to this process working its inevitable logic. Needless to say most scientists were skeptical. Extrapolating without seeing if the projections pass the sniff test is a fool’s errand. And in any case there’s no Law of Nature that sex determination has to be via the Y chromosome. Birds and reptiles have males despite a somewhat different sex determination system.

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Over the past ~2 million years, up until ~100-200 thousand years before the present, the lineages leading up to modern humans have exhibited gradually increased cranial capacities. Why? The implication of the shift in anatomy is that our brains are getting large, ergo, our cranium needs to expand to accommodate the increased size. Larger brains are not a trivial matter. Human brains account for on the order of ~25% of our energetic expenditures. In other words they’re expensive, so presumably they result in some major gain in fitness.

There have been many reasons posited for this increase in brain size. Please note though that this gradual increase predates the cultural creativity of the Upper Paleolithic, and the emergence of behaviorally modern humans ~50,000 years before the present. In fact there has been a mild reversal of encephalization since the Last Glacial Maximum ~20-25 thousand years before the present. So this is not as simple a conundrum as you might think.

About a generation ago the anthropologist Robin Dunbar came up with an answer which has been broadly persuasive to many. Using comparative data from other primates, as well as human ethnographies, he posits that it was increased social complexity facilitated by language which entailed greater cognitive demands on our lineage. The basic intuition is obvious. Keeping track of interactions across a dyad, two individuals, is not particularly demanding. But a “three body” social problem is not just incrementally more complex. As band sizes scale up to a dozen individuals, and groups of bands include hundreds (clans?), individuals have to keep track of a maddeningly complex network of relations. Dunbar’s surveys suggest that the real social network of humans (e.g., non-famous people whose personal lives you have some familiarity with) does not go much beyond 200 individuals. This is Dunbar’s number.

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Genetics has numerous uses. There are some biologists for whom genetics implies very specific chemical and physical properties of a particular flavor of DNA molecule. Consider a scientist focused on the biophysical properties of zinc finger proteins and the ZYF gene. Then there are biologists for whom genetics is a more abstract and evolutionary enterprise. David Haig and the late W. D. Hamilton fall into this class of thinkers. This is a way of looking at genetics as the scaffold or currency of evolutionary process. Finally, there are those for whom genes are simply discrete convenient markers to trace out historical and spatial patterns. The field of molecular ecology describes this attitude, though the application of phylogenetic techniques from the life sciences in linguistics illustrates the generality of these methodologies.

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George Johnson is out with a new book, The Cancer Chronicles: Unlocking Medicine’s Deepest Mystery, and is also now at the center of a host of controversies due to some of his conclusions after years of research and writing. You can keep track of the volleys back and forth at his blog, Fire in the Mind. But I want to you pay close attention in particular to a new piece in Discover (print edition), Prehistoric Times: The idea that cancer is a modern disease is a common misconception — one that the fossil record reveals to be untrue. Here’s the big bold assertion: correcting for the greater longevity of modern people the rate of cancer is no higher today than it was in the human past. This is a shocking claim, and bound to cause controversy.

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As we come up to the day celebrating American independence from the Britain there will be the standard revelries and reflections. Personally, I have no problem with that. A modicum of patriotism seems healthy in all, and if appropriately channeled a surfeit is often useful in the populace as a way to maintain civic engagement. That being said I did admit that in the positive and descriptive sense I am far more ambivalent about the consequences and rationale for the rebellion than I was as a child. I don’t accept that the American revolution was indisputably about Virginia gentry who wished to avoid financial ruin, New England fundamentalists yearning for oppression of Quebecois Catholics, or upcountry Scots-Irish chafing at the bit to explode into the western hinterlands, heretofore restrained by the Empire. But I believe that this narrative is as true as the story I was told as a child about an unjust and oppressive British monarchy battling the cause for the cause of freedom and liberty. When Patrick Henry declared ‘Give me liberty, or give me death!’, it was not a universal declaration. It was implicitly a call to arms for the rights of white male property holders in the context of colonial Virginia. This is not a palatable message for elementary school age children, so such subtle but true details are neglected in the standard narrative.

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