Is meat eating an evolutionary mystery? Humans are the only ones in the great ape family that eat a significant amount of meat. But human teeth which are designed for eating fruit cannot tear flesh easily, and digestive system has difficulty digesting it. Meat also is linked with a shorter life expectancy. It is said that fire drove the evolution of intelligence, but it would seem that it was the reverse since fire was invented quite recently, and intelligence had been increasing for a long time before it.