[Coolhand]

I dunno, I think the hints are there if you look hard enough.

For example, when Neville first catches the girl, the Leader actually races out into the sunlight to try and save her, something so unusual even Neville comments on it.

Later on, the seekers actually set a trap for Neville, using the same tactics and even the same rope snare that he used on them, demonstrating a certain level of intelligence and group thinking, and are seen using infected dogs that they've obviously domesticated and trained.

Obviously, they're mostly snarling and aggressive with Neville because even with some remaining human traits they are still infected and over-adrenalised, but there is enough evidence there to suggest that his assertion that they are now utterly beastlike and devoid of human traits is not quite accurate.