Reading time: 3 min.
Every being has to be egoistic in order to preserve his life. If a lion hunts a prey, it is not to offer it as a gift to the tiger. In the same way, if the farmer grows potatoes it is not to give it up on the market place without any other product in return. It is exactly because every individual is programmed to act in his own advantage that the continuation of life is made possible. Everyone preserves the fruits of his labor from the others, so that he can be sure to preserve his own life. In the same way the dog hides his bone, the humans guard their properties, lock their doors or put a fence around their lands. Under this perspective, every individual perceives his own life as worthier than the life of the other.
On the other hand, every being has to be altruist to preserve the life of his species. If the bird does not build a nest for his babies, and if the cow does not give milk to the calf, and if the parents do not work for their progeny, the survival of the whole species is endangered. Like within many animals, humans tend to share the result of their work with others; first with their family members, then with their tribe, their village or their city inhabitants and then with the people of their own country or even the whole humanity and other animals. The worker who pays taxes for example shares the result of his labor (money) with a community gathered under one flag and one government. The scientist or the composer shares the result of his labor (science or music) with all the humanity. And the veterinary makes the animals that he heals profit from his work.
In many species, it is this complex combination between work, egoism and altruism that determines its survival and its expansion (or extinction). In the case of the human species, it could be a high level of egoism and altruism both together that explains the quick and wide expansion of humans, putting in adverse position other beings like trees, monkeys and many other mammals and animals in general.