Fire gave rise to babies

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at:, or follow me on Twitter.

Homo sapiens have an unusual reproductive system. Whereas apes rarely have more than 5 children, humans typically had 20 to 25 children. What lead to the huge increase in the number of children? One possibility is fire, which lead to cooked food. One can reason from the opposite of this paragraph:

This hypothesis stems from a few modern observations. When you eat cooked food, you have access to many more calories than if you eat the same food raw. There are two reasons: Our digestive systems can extract more calories from a cooked steak (for instance) than a raw steak, and it takes much less energy to cook and eat a steak than to gnaw on a raw one for hours. Access to cooked food means a hominid no longer needs enormous teeth to break down all that raw meat and roughage into swallowable hunks, nor does it need as robust a digestive system to process it all. The combination of more calories and less complicated intestines means more energy can be devote to cogitating—hence H. erectus’ relatively big brains, which suck up a lot of calories. As evidence for his theory, Wrangham likes to point to the fact that modern-day humans can’t thrive on an all-raw diet—raw foodists tend to stop menstruating, precluding reproduction.

Some of the extra calories went into bigger brains, but a lot of it went into making more babies, so much that female homo sapiens now need the higher levels of calories to remain fertile.

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