I haven't had this "primal side" overcome me, if it even exists. And that's my biggest issue with the OP, because if anything, I have seen the primal side of an individual be used more for altruistic purposes than selfish purposes. I have seen injured dogs, and people who would consciously not help a dog, be overcome with guilt or something like that, devote their time and sometimes money into treating this dog. They have no relation to it, they don't know how it is, it could even attack them, but when they see an injured animal down on the ground, they help it. I don't know anyone that would even inherently or biologically want to kill it and eat it on the spot. Homeless people are another example, we see the downtrodden and some of us will naturally want to help them, though some of us may have different values on that. That's an iffier topic, a very interesting one really. Some of us may view humanity as more capable than other animals and thus perceive the homeless as less worthy of being helped, because they have a higher capacity to survive. But that's more of a logical conclusion rather than a biological one, so that's not the point.
The point is, instinctively, sometimes it's survival of the fittest, but when it isn't and we are faced with a creature in front of us, human or non human, that is in pain and at that point, weaker than us - we are instinctively thinking not just about ourselves, but about the species as a whole. We have companion animals, we have other humans, we have symbiotic relationships to consider here. Why should we sacrifice these things? It makes it harder for us to live. We are programmed, biologically, not to do the things that the OP said we COULD do, biologically. Our assigning values and making choices is nothing that society taught us, we were born with a moral code. To violate that code is literally violating your own survival instinct.