Berzerker
Deity
But for most of humanity's existence, "the other" describes the next tribe over. It wasn't articulated in terms we comprehend as differences of "race". And when people did begin to draw larger, more abstract distinctions, it was in terms of civilisation and barbarian, or believer and infidel, terms which do not clearly lend themselves to a racial framework, and in the latter case tends to run directly against it. It took until the sixteenth century, at the earliest, for this allegedly-innate behaviour to manifest itself, and even then only in certain parts of Europe. So even if you might make the argument that hostility to out-groups is innate, it is still necessary to explain racism as such: to explain why the in-group/out-group distinctions have been drawn in these particular ways, and why they have proven so pervasive and so enduring.
"Race" has always been with us, even when we were altogether ~200-300kya the neighboring tribes were various hominids and when we expanded out of Africa the new neighboring tribes were the descendants of those peoples, not us. Civilized, barbarian, believer, infidel, these just show how important distinctions are to us. We evolved to make distinctions because existence was dangerous.