In Most Vertebrates,full Siblings Share as Many Genes with Each

In most vertebrates,full siblings share as many genes with each other,on average,as each one does with either parent.One might predict that serious conflict between siblings should be rare and altruistic behavior should be the norm,given that siblings share the same "genetic interests." As anyone who has ever had a brother or sister knows,this is not always the case.In fact,in a number of bird species,notably eagles and other raptors (birds of prey),females usually lay two eggs; soon after hatching,the larger chick pushes the other chick out of the nest,or otherwise attacks it and tries to kill it.(This behavior is known as Cainism,after the Bible story of Cain and Abel.)Generate a hypothesis to explain this behavior in evolutionary terms.Can you apply this hypothesis to human behavior?