Not to offend any passing vegans out there, but eating meat is what helped us humans to stay on top of the food-chain.

A study conducted by researchers at the Lund University in Sweden showed that eating meat not only made our brains bigger, it also allowed humans to breastfeed their children for shorter periods and give birth to more offspring. Because the brains of meat eaters' offspring developed faster, they could stop feeding their child sooner and reproduce again.

The researchers figured this out by studying diet patterns from 70 species, and found that meat was the deciding factor in evolutionary success. Here's what they had to say about the findings:
The difference between us and the great apes, which has puzzled previous researchers, seems to depend merely on the fact that as a species we are carnivores, whereas gorillas, orangutans and chimpanzees are herbivores or omnivores.