Alex Gregory's excellent cartoon in The New Yorker works on many levels today.

Palaeoanthropologists believe that life expectancy at birth in the Upper Palaeolithic was 32 years, although research based on contemporary hunter-gatherer populations estimates that by the age of 15, life expectancy was an additional 39 years, totalling 54 years.

For Homo erectus in the Lower to Middle Palaeolithic, meat played a major role in our evolution and our larger brains; the high-quality diet caused humans to have smaller guts, releasing energy to be used by the brain. In terms of development, raw meat was a big step; cooked meat was a huge step.

Ironically, life expectancy at birth in the Neolithic was 20 years. The Neolithic period also saw the brain size reduction in Homo sapiens.

Learn more about the lives of our ancestors in the Origins section, and watch the short film featuring Cassandra Turcotte, from The Center for the Advanced Study of Hominid Paleobiology (CASHP) in Washington D.C., explaining aspects of human and cultural evolution: 

http://www.bradshawfoundation.com/origins/oldowan_stone_tools.php

Read the article on Palaeolithic diets:

http://www.bradshawfoundation.com/news/origins.php?id=Palaeolithic-diets

and for The New Yorker:

http://www.newyorker.com/