There are two myths about human nature. One is the myth that we are a social species, the other is the myth that we are a predatory species.
Why are they myths? Because they assume that human nature is only predatory or social. These are simply modes that people assume to fulfill their own interests or get what they want. Humans can be both social and aggressive, and many other things, especially in between. In the end, human nature is based on desire and will, it just manifests in both social and aggressive ways and everything in between.
Perhaps, these myths originate from the desire to only perceive a single 1-dimensional idea of human nature. It is a desire that arises from ignorance, and a refusal to see the many ways human nature can manifest itself. We all want to get what we want, fulfill and exert our will and desires, but this manifests in many different ways, be it aggressive or otherwise.