It's an interesting perspective to think of pre-agricultural (the 40k line is admittedly before that) humans as not standing out amongst other fauna, but on the

It's an interesting perspective to think of pre-agricultural (the 40k line is admittedly before that) humans as not standing out amongst other fauna, but on the other hand there is no reason to imagine them standing out any less than groups that stayed hunter-gatherers into modern times and those certainly do/did. They would not have left many traces identifiable after tens of millennia though, not now, not then. General intelligence, by itself, appears to be just one possible strategy for adapting to the environment, not inherently superior considering that many species get along just fine with survival tactics "hardwired" for their environment. But it sure gives faster adaptability and humans had expanded into very diverse environments deep in the stone age. What eventually set the human brain apart is the old cliche distinction of opposable thumbs. Back to topic, few things illustrate the value of our hands better that watching a crow headbutt an object with its beak, stop to ponder the results, then headbutt again because what other option does it have?