In honor of Halloweek, I thought I’d share a terrifying little tidbit I learned from a great lecture by professor Henry Gilbert.  At the 1 hr 14 min mark in the below video he mentions a theory that the really thick crania observed in Homo Erectus may have been an adaptation to the fact that they were bashing each other’s heads in.  This is wildly speculative but this might also help explain extreme selection for brain size we see in Erectus, since 1) winning fights requires brain functions like intelligence and physical coordination, 2) head butting people requires a large cranium, 3) some research claims big brains can absorb more insults though this is disputed, and 4) selection for brain size was paralleled by selection for height, which is also useful in combat, especially head butting.

Another point Gilbert makes is that the huge brow ridges of Homo Erectus might be explained by their  robust cranium combined with small frontal lobes (compared to modern humans).

In my last article I discussed the opening scene in 2001: A Space Odyssey, which really emphasized Raymond Dart’s killer ape theory that was popular in the 1960s but has since fallen out of favour, which is a bit surprising given the facts that 1) violence is an obvious selection pressure for intelligence 2) humans are incredibly violent creatures and so are our ape relatives the chimpanzees, and 3) genetic evidence confirms that anatomically modern humans rapidly replaced all other “human” species with only minimal admixture.  On the other hand, there isn’t much evidence the replacement was violent, other than a controversial claim that we ate Neanderthals and the fact that caves occupied by Neanderthals were often taken over by modern humans quite rapidly.

One problem with the killer ape theory is that a recent paper claimed that contrary to Gilbert, cranial thickness was not exceptionally extreme in Erectus.