I think about Luke Jostin’s analysis of the growth in cranial capacity in the hominin lineage from last spring a fair amount. In particular, in the comments he notes:
The data above includes all known Homo skulls, but none of the results change if you exclude the 24 Neandertals. In fact, you see the same results if you exclude Sapiens but keep Neandertals; the trends are pan-Homo, and aren’t confined to a specific lineage (though if you exclude Erectus everything goes skewiff, as you’d expect).
That brain size increases gradually in all lineages is another pretty strong argument against brain size being a macromutation.
I’ve put the species in the data file, if you want to play around with it yourself.
A particular configuration of traits or genes aligned early on in the existence of Homo seem to have resulted in increases in cranial capacities across divergent lineages. Robert J. Sawyer’s The Neanderthal Parallax series may be less fantastical in its premise than we would have thought.
