Apparently, cooking vegetables may have been the impetus for human civilization.
Robin Nixon at Live Science reports:
For a long time, we were pretty dumb. Humans did little but make “the same very boring stone tools for almost 2 million years,” he said. Then, only about 150,000 years ago, a different type of spurt happened — our big brains suddenly got smart. We started innovating. We tried different materials, such as bone, and invented many new tools, including needles for beadwork. Responding to, presumably, our first abstract thoughts, we started creating art and maybe even religion.
To understand what caused the cognitive spurt, [Researcher Philipp Khaitovich of the Partner Institute for Computational Biology] and colleagues examined chemical brain processes known to have changed in the past 200,000 years. Comparing apes and humans, they found the most robust differences were for processes involved in energy metabolism.
In most animals, the gut needs a lot of energy to grind out nourishment from food sources. But cooking, by breaking down fibers and making nutrients more readily available, is a way of processing food outside the body. Eating (mostly) cooked meals would have lessened the energy needs of our digestion systems, Khaitovich explained, thereby freeing up calories for our brains.
But what about meat? Perhaps it was roast beef, not lentil soup, that led to higher powers of cognition? Possibly, but less likely, in my opinon. Animal cells have membranes, which are easy for the body to break down. Plants have walls, made of cellulose which are much more difficult: cooking greatly facilitates their digestion.
Cooking meat can very slightly increases the caloric density, but only by driving water off, making it denser. However, the total calories from available from the meat decreases during cooking: fat is driven off and proteins are broken down. Cooking plants boils the water inside the cells, rupturing the cellulose cell wall. This makes the calories and other nutrients vastly more bioavailable.
It also lets you eat a more diverse variety of plants; many wild plants are toxic in their uncooked form, and heat denatures the toxins. In many more, heat won’t denature the toxins, but repeated boils in changes of water can get rid of them, like the tannins in tea. And, apart from a few hunter gatherer societies that living in incredibly barren environments, such as the Innuit, most hunter-gatherer groups get about 80% of their calories from plants.