Cows and chickens are not humans. That is a stupid comparison.

If we wouldn't have eaten meat as a species, we would be no more intelligent than gorillas.

[link to www.livescience.com]

"One study, published last month in the journal Proceedings of the National Academy of Sciences, examined the brain sizes of several primates. For the most part, larger bodies have larger brains across species. Yet humans have exceptionally large, neuron-rich brains for our body size, while gorillas — three times more massive than humans — have smaller brains and three times fewer neurons. Why?

The answer, it seems, is the gorillas' raw, vegan diet (devoid of animal protein), which requires hours upon hours of eating only plants to provide enough calories to support their mass.

Researchers from Brazil, led by Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro in Brazil, calculated that adding neurons to the primate brain comes at a fixed cost of approximately six calories per billion neurons.

For gorillas to evolve a humanlike brain, they would need an additional 733 calories a day, which would require another two hours of feeding, the authors wrote. A gorilla already spends as much as 80 percent of the tropic's 12 hours of daylight eating.

Similarly, early humans eating only raw vegetation would have needed to munch for more than nine hours a day to consume enough calories, the researchers calculated. Thus, a raw, vegan diet would have been unlikely given the danger and other difficulties of gathering so much food.