<p>I’m not sure how your second sentence is relevant. </p>
<p>the conventional explanation for why the average brain-size decreased from 1500-1300cm^3 is something along the lines of - we domesticated ourselves by becoming agrarians, and it is well established that domestication reduces the brain size in animals.</p>
<p>This sounds reasonable to me - we stop hunting as much, our lifestyle changes dramatically, and the parts of our brain that was responsible for that the things that are now not needed shrink. I don’t suppose to know how that happens of course.</p>
<p>the second thing i said - about height - is better evidence for the agrarian diet being lower quality and less healthful than the hunter and gatherer one.</p>
<p>an alternative explanation is that more, less-fit people (smaller people) were able to pass on their genes in agrarian societies because you didn’t have to be big and strong to hunt enough meat to survive. this sounds plausible to me too.</p>