New Scientist has as article arguing that the expansion in hominid brain size that occurred about two million years ago was due to the ice age which allowed an energy burning, heat generating brain to develop with sufficient environmental cooling.
Actually, it’s worth a read as it’s not as odd as it sounds, but it joins an ever growing list of theories that attempt to explain how our forebears ‘suddenly’ seemed to experience evolutionary brain expansion.
A diet high in meat.
A diet high in starch.
The development of cooking.
Essential fatty acids and schizophrenia.
An unspecified “special event”.
The trouble with some of these theories is that they typically assume that brain size is always related to greater intelligence, which is not necessarily the case, and they don’t always take into account the ratio of brain to body size, which seems to be more important than just brain size alone.
Interestingly, almost all the interest is on brain expansion and no-one seems particularly interested in the fact that the brain has shrunk about 10% since the Late Pleistocene, about 30,000 years ago.
You can have a great deal of fun coming up with evolutionary theories for that one. Just pick a key human activity that emerged around the same time.
Personally, I blame language, religion and karaoke.
Link to NewSci on brain science and the ice age.