This could very well be enough time to shape different subphenotypes' ability to thrive (or not) or be well adapted to quite dissimilar foodstuffs and associated activity. I kinda think it could have an effect on digestive enzymes or gut bacteria over all that time too and if there was some symbiotic benefit that had built up over all those millennia it would be a shame to lose it for some dumb reason or another. It could happen.

Especially for those cultures who were more niche, or remained relatively more isolated for most of those millennia compared to other cultures.

Herd animals can be involved either way since some could be hunted and others more commonly raised through farming, which is more like gathering than hunting. That can be the same species too, so you do have to look way back.

With non-domesticated herds I don't know of a culture that largely milked American bison, they were mainly a hunting or trapping target. Reindeer OTOH did have cultures develop who thrive on their milk, and herd the deer across their harsh natural landscape in what basically became a pseudo-domesticated approach.

I would imagine there were alternative cultures herding the same species in the same harsh environment, or similar climates whether isolated or not, and whether the humans or pre-humans were similar subphenotypes.

For any prey or sustenance species whether plant or animal, if it's been around in a very similar form for a million years or more, odds begin to rise when you think of the possibility for a niche human culture to evolve and become virtually dependent on a that particular species in a symbiotic way. Since that's the formative environment in which those humans arose. When some species become truly domesticated that's where you seem to see the species themselves become selectively evolved in the most obvious ways. What about when the target species or environment does not evolve (like when it's almost finished evolving since it's been at it a million years) as much as the fast-moving pre-humans were evolving? And what about when the real smart innovative ones took to the field, the Sapiens we've all been cheering for? Modern humans seem to be able to evolve to adapt to their environment in some of the most interesting ways. Probably a lot faster than the environment adapts to them.

From what I've seen, I guess people are still not that smart. It's possible for humans hunting or herding to become locally extinct if a situation were to arise one day where everything ended up being consumed for meat, and even though there were plenty of other herds of the same species & genotype, scattered across the wasteland, having none within reach the over-consumers were SOL.

Could amount to complete loss of a human or pre-human unique phenotype which was what realistically went extinct when the very species they hunted or trapped did not.

Just the opposite outcome from the commonly assumed one-sided extinction of a target species by similar human overhunting.

While hundreds of miles away a dissimilar culture survived the same harsh conditions due to habitually consuming more milk than meat. Habits built over millennia. And some of these cultures may very well exist to this day.

Now you could consider the distribution of those who thrive most primarily on meat, milk, or plants, and the descendant combinations that are possible as disparate cultures have become drastically less isolated over the more recent decades & centuries than ever before possible. Looks like it's hard to tell but meat may be the most popular and who knows it may be from having a hunter instinct. Or it could be plants and agricultural meat, where people surely would have some dedication to making things grow or they would have been SOL. Milk appears to be a solid minority niche, but as well-established as anything.

No wonder people got tired of the limited diet that cave men had, it was pretty boring for a few millennia there.

They didn't know what they were missing with a gourmet meal that they don't have to hunt for nor grow anything on a farm.

Although there's still bound to be some holdouts who would just "kill" for a good Brontoburger about now ;)