Why do animals recognize relatives?

Social biologists believe that like-minded blind date is an animal instinct and a survival adaptation. Animals are animals after all, and their survival has a goal, which is to spread their own genes. If Yan Yan doesn't recognize her relatives, she may give the food she worked so hard to find to other birds and starve her children. New the Monkey King wants to kill the descendants of old the Monkey King, because these little monkeys don't have their genes.