The human extended phenotype

I think there is something to the hypothesis that we as a species are self-domesticated, but a new preprint really doesn’t change my probability up or down, Comparative Genomic Evidence for Self-Domestication in Homo sapiens. Notwithstanding my own participation in some comparative genomic work, a lot of the conclusions from this field are as clear and obvious to me as the above figure, not very.

To be fair at least the authors of the preprint have a hypothesis they’re testing, the “domestication syndrome” as cause by the neural crest gene modification. Two major issues I’d bring up: it’s comparative genomic because of a paucity of samples, and, tidy explanations often don’t pan out.

Genomic analysis of ancient genomes is very preliminary. Phylogenomic work, which establishes relationships between lineages, can accept a noisy and poor marker set with only a few representative samples. But when looking at population genomics one should at least have either really good data on a small number of individuals, or, more preferable, good-enough-data on lots of individuals. The ancient genomic data set for hominins is not rich enough that I’m confident about any but the most obvious and clear differences between our closest relations and ourselves. The reality of gene flow across populations also adds a confounding element, because it might not be implausible that “modern” alleles actually derive from another ancient lineage, and our modern forebears exhibited the ancestral state.

Second, the neural crest hypothesis and a general model of domestication is rather attractive. I myself find it intriguing, and am curious from a professional scientific perspective. But, attractive hypotheses often do not pan out, and gain early attention because scientists are human, and exhibit some bias and hope. A case in point, mirror neurons has stalled as a silver bullet to explain all sorts of unique aspects of human cognition. Neural crest models are part of the long quest to establish the genes which make us unique and human, even though I’m not even sure this is a wrong question.

The preprint did remind me of an excellent book I read over 10 years ago, The Cultural Origins of Human Cognition. I am much more well disposed toward the thesis now than I was then, in large part because I now longer hold to a “big bang” theory of the origin of modern humanity due to a behavioral revolution triggered by a rapid suite of genetic changes. Rather, I suspect a cultural model where there is reciprocal feedback with genetic changes in a sort of ratchet has a lot more utility, in part because the gap between “archaic” H. sapiens and our own ancestors was I believe much smaller in many ways in relation to behavior than we’ve assumed until lately. Finally, the genetic evidence of lots of lateral gene flow across these distinct branches is indicative of more complexity in the origin of humanity than we had previously understood.

There is also the whole idea of “self-domestication.” I think perhaps it needs to be more explicitly formulated in an ecological sense. Rather than self-domestication, what occurred is that a host of species began to inhabit an evolving “extended phenotype” which humans were a motive engine within. But we need to be cautious about overemphasizing our agency. Once human societies became agricultural beyond a certain point it is not not possible to revert back to hunter-gathering lifestyles without migration or mass die off. In some ways we are as much pawns in the forces unleashed by our original choices and actions as the domestic animals and plants and parasites which have come along for the ride.

Citation: Comparative Genomic Evidence for Self-Domestication in Homo sapiens, Constantina Theofanopoulou, Simone Gastaldon, Thomas O’Rourke, Bridget D Samuels, Angela Messner, Pedro Tiago Martins, Francesco Delogu, Saleh Alamri, Cedric Boeckx, doi: https://doi.org/10.1101/125799