Genetics The reason a person would die for eight of their cousins or however many that they have has to do with genes. The genes that you received came from my parents. The genes come from both parents not just one. The genes that they received came from their parents. Your father's brothers and/or sisters share the same genes, some may be dominant in one and recessive in others. The same occurs with your mother's brothers and/or sisters sharing the genes. When your aunt and/or uncle has kids the genes that they received from their parents are passed on to their children. Which means that you have a few genes in common with your cousins. Due to they got them from their grandparents who gave them to your mother or father, however this takes place on both sides of the family your mother's and fathers. This why a person should be willing to die for there cousins due to the fact that they have some of the same genes in common with you.
Which means your genes are being carried on by your cousins not just you. Even though it is only a 25% chance that they will have some genes in common with you. Due to the fact that know they have a new set of genes that you don't have. You wont have the genes that your in-law aunt or uncle has. A person could even go on to say that they would die for at least two maybe four of your second cousins. The number of chances that you might have some of the same genes as them gets smaller, because they now have two different family members genes that you don't have. That is why a person can go on to say that they die for eight of their first cousins as well two maybe even four of their second cousins.