The evolution of altruistic behaviours is unclear. There is no single universally accepted reason. The most common argument is probably that it was selected f

The evolution of altruistic behaviours is unclear. There is no single universally accepted reason. The most common argument is probably that it was selected for in the same way your genes would have a survival advantage even if you die while helping your cousin or sibling or just fellow human survive. Because they're almost genetically identical to you, their survival is almost the same as your survival, from the gene's perspective.