My cat would carefully lick out the yolk and leave the white, if I cracked a raw egg into a bowl for her.
It is an interesting example, thanks, and it's an intriguing question, but a better clue for Paleolithic human behavior would be wild primates, so I looked into it and did find a report and an example of yolk-favoring primates, though also a couple primates that appear to enjoy the white as well:
Monkey eating eggThis monkey eats the white and yolk, although rather sloppily, but one of the commentators says the other monkeys only eat the white when they're "really hungry."
Monkey eats a raw eggThis monkey also appears to be eating both the white and yolk, even though rather adept at the process, and enjoying it quite a bit, though some of the white did still spill out.
A monkey eating a raw egg in BaliThis monkey favors the yolk, though perhaps in part because he dumped the egg contents and the white washed away, but he still could have licked the remnant of the white if he had wanted to.
I don't have a lot of accumulated evidence yet, but it's looking like yolks are definitely favored (no surprise there given general human preference for yolks, including my own), and whites are sometimes or often discarded, but not always. My guess is that the yolks of quail-size eggs and smaller would be less frequently discarded, except for spillage, and maybe fertilized egg whites would also be discarded less often? Maybe the whites consumed in these videos were fertilized? It seems more plausible that the white-eating monkeys were just hungrier or less well acquainted or adept with eggs. Overall, I guess if these wild behavior examples were to suggest optimal behavior, then that would suggest that it would make sense to eat mostly yolks but sometimes also whites. I do discard some chicken-egg whites as it is (mainly unfertilized whites), but eat most of them. Maybe I'll try discarding more of them for potentially better optimization. It's looking to me like there's probably more egg-white-discarding in the wild than I guessed, including much of it accidental.
Cooked egg whites are even less appealing to me than raw whites--too bland and boring and too much fuss to bother with, though maybe I could liven them up with honey. I actually like duck egg whites and would prefer not to discard any of those and wonder if wild monkeys would eat those more frequently than other whites. I also wonder why they taste better to me than chicken egg whites. Anyone have any idea?
This raises another interesting question: does the casual discarding of whey-rich whites by some primates and a cat, and the lack of whey products in the wild, suggest that whey protein powder is not the superfood it's made out to be? Of course, it's all speculation at this point without more evidence and analysis, but it's fun to ask science-related questions, investigate and learn.