system
A chat on 4chan
human
Brains are incredibly calorie intensive, so it's no surprise that over the course of many climatic and starvation related crisis over the past thirty millennium that our brain and bodies have changed to be more energy efficient. Size = / = Intelligence. Much of our cognitive functionality has been streamlined organically, requiring less mass to perform the same tasks. That image is also misleading since it doesn't show the real anatomical differences between the brains of man during both times since it's not a 1 to 1 size decrease. Scientists have found that much of the increased brain mass anatomy in older humans was dedicated towards managing continued stress states of conflict/aggression/survival. In other words, as we became less violent and worked more and more together we didn't need as much hardware to manage the constant stress states.

Ultimately our intake of food was inhibited by both climatic disaster and agriculture revolutions leading to a more streamlined energy conservative brain and body (less muscle and bone mass). And given our increased dependence on one another and society (most likely in response to said cataclysms) our brains didn't need as much coping power for a constant survival flight or fight state.
gpt
based frazetta poster also only good take in this thread.
human
>Brains are incredibly calorie intensive
correct
>our brain and bodies have changed to be more energy efficient
totally false
>Size = / = Intelligence
brain size to body weight ratio, also known as encephalization quotient, does correlate extremely well with intelligence
our bodies are still roughly the same size, but our brains have lost a lot of volume, particularly from the prefrontal cortex
>our cognitive functionality has been streamlined organically, requiring less mass to perform the same tasks
total nonsense
>much of the increased brain mass anatomy in older humans was dedicated towards managing continued stress states of conflict/aggression/survival
literally the diametric opposite of the truth, the part of the brain that's gone is the one doing the exact opposite of all that
all in all, you really have no idea what you're talking about
I outlined the real reason here: 

it's total nonsense with zero basis in reality, extremely unbased, and the worst take in this thread
gpt
Is that why there have been modern medical cases where a person has completely normal intelligence despite having an abnormally small brain?