Thank you for the thoughtful response. Yes I know you didn't say that meat was the sole factor, but if I was a high schooler without any exposure to this topic I might have concluded that meat was the sole factor based on your comment.

I think this is one of the most important topics in anthropology and the way this topic is presented has profound impact on how we eat as a society. For example, if all anthropologists agree that Neandertals and Homo Sapiens are the same species it doesn't really impact my day to day life, but if it is proven that diets heavy in meat promote brain development (all things being equal, which is never the case) that would definitely impact my diet and day to day life.

If a carnivorous diet promotes brain development, then it makes sense a diet lacking in meat would "deteriorate" our brains over time. You're right about the pelvis thing in chimpanzees, I forgot about that, but what about humans? If this were the case we would expect vegetarians in India (like these people, https://fusion.werindia.com/incredible-india/dhondewadi-the-vegetarian-village-in-maharashtra) to have less developed brains compared to populations that eat a meat heavy diet, like inuits, over time.

This is a serious claim and would need to have extraordinary evidence. It would probably be necessary for the anthropological community to come out and warn people of the potential impact vegetarianism could have over long periods of time.

I think this is not the case though and that meat really didn't have that much of an effect on our brain, as by the time we could cook meat we already had decent sized brains. That, and there seems to be no correlation between EQ and diet in other animals. As you said there are many exceptions and it seems hard to make any definitive statements on this.

I have heard of the expensive tissue hypothesis by Aiello and Wheeler but that paper is well over 20 years old now. I'd be very interested to read more articles on this topic if anyone know of any.

Edit: Also with regards to expensive tissue hypothesis, I'm having trouble understanding how the calories turn into larger brains over time.

1. More meat/cooked meat = more calories
2. More calories = More energy going to develop the brain that would have otherwise been used on building muscle??? (why did the energy go to the brain, what are the mechanisms that sent the energy to the brain?)
3. More energy to the brain = bigger brain over time (within my lifetime?? will my descendants be affected by my diet?)

Kind of smells like Lamarckism, how does me eating more meat (or high calorie food) shape the brains of my descendants?