Human Nature vs. Socialization

So, we have been talking a lot about the order in which we as humans place importance on life. We first choose our interests, then our families interests, friends, neighbors, pets… and so on, not necessarily in that exact order depending on the person. But for most of us we would choose to save our own lives or the lives of our children over our pet’s life or the life of our neighbor. I think we naturally choose humanity over animals because of our nature. If there were two humans and one dog on an island and the dog and one of the humans had somehow gotten injured, the second human would most likely give the last of their medical supplies to the injured human and not the dog.

Why do we do this? Is it just in our born human nature to want to choose the human over the animal or have we been socialized to do so because of social norms/pressures, biases, and “isms?”