I was just blown away by this conference at UC San Diego.
Half a dozen professors at the Anthropology Institute summarize the latest hominid theories.
1) Early hominids were less ape-like than our imaginations drew and displayed in museums in the past. We imagined homo erectus, the first to stand upright, to have a gourd-like rounded rib-cage like an ape, except it turns out they have a tighter one like we do.
2) The last lecture by the older woman was the keynote really. The Neanderthal had AS BIG a brain as modern humans. Except to raise a such a large brain, you need to have a well regulated body temperature for at least until the child becomes independent to feed / hunt itself. Early hominids may have had comparable brain sizes, but unless their bodies developed to match such a big head (human babies have giant heads compared to their bodies), and the body grew at a rate which could sustain the giant head — having an ape’s body but large brain made a difficult problem to regulate the temperature and rear children to a surviving age.
Our species was the first, to have a magical fit, between a lean and sustainable body with such a large brain. We quickly wiped out the other ones, if climate change didn’t do the rest.