Having a brain capable of deciding not to eat meat may in fact be due to …. eating meat.
The argument is that our large brains are very expensive, nutritionally, to keep going.
Some other part of the body (with reference to the \”standard\” mammallian blueprint) must have shrunk in terms of the nutrition required to keep it going to allow the brain to take so many resources.
Heart, lungs, liver, kidneys, the other expensive bits to keep going, are largely unchangeable given the size of the total animal.
But the gut is changeable. It\’s possible to have an \”expensive\” gut able to process lots of veggies….and cellulose etc, so that grass eating becomes nutritious. Or you can have a cheap gut which cannot process these….and therefore you need to be eating meat as it\’s denser in that nutrition required.
Which leads to the conclusion that you cannot have intelligent herbivores because they need to put so much energy into running their guts that the brain cannot grow large, thus only carnivores or omnivores can become intelligent.
No, this isn\’t an explanation of why vegertarians are dullards: neither that their small brains allow them to get away with it nor that their getting away with it makes their brains small.
But it ought to.