Human is as human does

Human lineages as a whole have been tending toward increased cranial capacity over the past 2 million years, including the one that led to modern people. That is the finding of Luke Jostins several years back when he crunched the paleoanthropological data. This is one major knock at our specialness as humans, since it seems our cousins were progressing through the same stages of development as our own ancestors, before they were swept away by and large. A new paper in Nature reports that H. erectus engaged in more cleverness than we had expected, Homo erectus at Trinil in Java used shells for tool production and engraving. John Hawks has already commented on it so I won’t offer my two cents, as they aren’t worth much. But, it does suggest that we’ve underestimated “early humans.” John points out that many ancient finds might be reinterpreted with a different set of expectations.

On a related note, a new paper attempted to find evidence for classic selective sweeps in our lineage comparison to the Neandertal and Denisovan populations, something feasible because of the existence of high quality ancient genomes. Let me quote from the abstract:

… We tested sites at which humans are fixed for the derived (i.e., nonchimpanzee allele) whereas the Neanderthal and Denisovan genomes are homozygous for the ancestral allele. We observe only weak differences in statistics indicative of selection between functional categories. When we compare patterns of scaled diversity or use our ABC approach, we fail to find a significant difference in signals of classic selective sweeps between regions surrounding nonsynonymous and synonymous changes, but we detect a slight enrichment for reduced scaled diversity around splice site changes. We also present a list of candidate sites that show high probability of having undergone a classic sweep in the modern human lineage since the split from Neanderthals and Denisovans.

As the heirs of the snottily termed “anatomically modern” humans it is hard for us to not think that we came and conquered due to some glittering genetic mutation. The lack of pervasive classic sweeps since the divergence of “us from them” confirms that evolution didn’t go into magical overdrive in our lineage. We are not “more derived” on the Great Chain of Being with chimpanzees as a reference, but simply different. The laundry list of candidate sites will be interesting, but must always be interpreted cautiously. These sorts of results dovetail nicely with the reality that the behavioral chasm between “archaic” and anatomically modern humans until about ~50,000 years ago wasn’t that large at all. Though changes in the fossil and archaeological record can seem punctuated and is discontinuous, I wouldn’t bet against the possibility that genomics points to a dynamic where change between the lineages was driven by gradual evolution via selection on standing variation.

Finally, there’s a recent paper on the nasal anatomy of Neandertals which made some media headlines recently. The most sensational conclusion drawn from nasal architecture is that Neandertals were a separate species from us. As I don’t know much about anatomy, and I don’t care much about species status, this isn’t something I’ll explore beyond just reporting that. But, another aspect is the fact that it seems the morphology of Neandertals has often been compared to modern humans, and judged by modern human standards. It seems entirely likely that Neandertals had different adaptations and an alternative morphological trajectory from our own lineage. Though I don’t think they were as different as some scholars would like to think, we need to be cautious about turning them into a version of ourselves, or at least our Out of Africa selves. The hominin lineage contains multitudes, and we are but one.