One of the things that happens in the evolution of Homo erectus,
especially the African Homo erectus, into later humans--later Homo--
and this would also include Neanderthals--is that the brain increases in size.
And this results in a different--not only a larger size of the braincase
but also a different shape.
So what happens is that the frontal bone and the parietal bones all fill out--they expand.
They become more rounded and also the whole head becomes more rounded.
And you can see this here.
The Neanderthal is still quite low and elongated as compared to modern human,
but it certainly is a lot more filled out than something like that.
So--but the easiest way to tell a Homo erectus skull if you ever have to take a test about this
is to actually use a pencil test.
So you can always balance your pencil on top of the Homo erectus brow ridge
because what happens is that the frontal bone is rather flat
and there is a--almost a gutter like depression behind the brow ridge, right?
This doesn't happen in later Middle Pleistocene humans or Neanderthals
or, of course, modern humans, but it happens here in the Chinese Homo erectus as well.
So let's try it with a Neanderthal and let's see what happens here.
We'll try to balance the pencil and it rolls off,
and this is because there is no longer a gutter-like depression here.
The frontal bone is filling out and resulting in this steeper slope.