Why did ancient hominids have larger brains than us?

My opinion is that no one knows

a reply to: glend

You're comparing a human, even a primitive human with a bird?
Yeah that doesn't sit well with me.
There are many predators out there with superior skills and physical adaptations. Sight ,hearing, scent...
Those predators seek opportunities suited to their skills.
Humans manipulate the environment to suit theirs.