The problem is that bone/muscle/fat mass doesn't mean more neurons connecting to that mass, so that bulk is mostly irrelevant. One place where it might matter i

The problem is that bone/muscle/fat mass doesn't mean more neurons connecting to that mass, so that bulk is mostly irrelevant. One place where it might matter is if Neanderthals had more skin surface area and the same density of touch receptors, but that is a pretty marginal difference and might not even be true. Their brains were notably, disproportionately larger, mostly due to having notably larger eyes.