Most people don't like to be told they have a big head, but some scientists might actually consider that a compliment. Humans have much large skulls than apes and since humans are much more intelligent there's been a long-standing belief that skull size indicates level of intelligence. That's why evolutionists tend to interpret larger ape skulls as advanced apes and smaller human skulls as sub human.
But this evolutionary story has multiple problems. Neandertals were supposedly primitive, often portrayed as sub-human, but their skulls are actually bigger than ours. Also the winner of the 1921 Nobel Prize for literature had a tiny skull, 25% less than today's average volume.
The reality is, skull size is a poor intelligence indicator. After all, the average skull size of men is greater than that of women, but there is no consistence difference in intelligence.