I think that this was easier explained in "The Selfish Gene". Individual altruism is an emergent characteristic of a selfish gene.
I risk my live 10 times to save others until I die without off-spring. It is altruistic for me, but the gene has saved 10 people that are probably related to me. That means that the gene has a probability over 10% to be in that other individuals it is a win for the gene.
From my point of view it sucks, I don't have offspring. But the gene survives and prospers. This is still more extreme in species like bumblebees where sisters share 75% of their genes.
For monozygotic twins there is a similar case. From the gene perspective is irrelevant if one survives or the other, even that it is really important for the individuals.
I think that this was easier explained in "The Selfish Gene". Individual altruism is an emergent characteristic of a selfish gene.
I risk my live 10 times to save others until I die without off-spring. It is altruistic for me, but the gene has saved 10 people that are probably related to me. That means that the gene has a probability over 10% to be in that other individuals it is a win for the gene.
From my point of view it sucks, I don't have offspring. But the gene survives and prospers. This is still more extreme in species like bumblebees where sisters share 75% of their genes.
For monozygotic twins there is a similar case. From the gene perspective is irrelevant if one survives or the other, even that it is really important for the individuals.