And so speculates a character:

Hard times just seem to help evolution. The Pleistocene Ice Age and pluvials could have killed off all the plant-eating hominids. But instead, the rough climate and the vegetation changes seem to have encouraged some of our ancestors to become meat eaters. And if you eat meat, you don't have to spend so much time hunting food. You can sit down and learn to think.

Climate-diet-cognition. Tempting series. And some how if you think about it, it's a bit off.

How one spends time. Certainly that is tied to freedom to led the mind wander and to contemplate. To ponder and pause. But can such mental activity be congruant with berry picking, grubbing or seed gathering?

There is the time spent digesting.

Sitting down and thinking. So one way of reading the story is that meat eating did not so much expand free time for the hominids as slow them down.

The remark is given simply in passing and the discourse passes swiftly on to other considerations. Pity the characters in conversation were not sharing roasted flesh.