Some modern biologists view evolutionary development from the viewpoint of the selection and reproduction of genetic material, rather from the viewpoint of selection and reproduction of individuals. This makes the difficult-to-understand concept of individual altruism somewhat easier to model. From a gene’s point of view, it makes no difference if future copies of the gene come from the individual it is currently inhabiting, or from another individual carrying the individual gene. Thus an individual might sacrifice its life if in doing so it would increase the probability of others carrying identical genes to reproduce.
This has been formalized mathematically in Hamilton*'s rule,* which states that
b > c/r,
where c is the cost incurred by the altruist (the donor), b is the benefit received by the recipients of the altruism, and r is the co-efficient of relationship or percentage of genes shared between donor and recipient. I find this rule easy to remember from the quip “I’d lay down my life for 2 brothers or 8 cousins.” (since brothers share ½ their genes, and cousins 1/8)
Hamilton’s rule in this form is a bit simplistic, as altruism also seems to be influenced by the reproductive capability of the recipient.
Although the operation of kin selection does not require the recognition of close kin, such a recognition would make the process much more efficient. It is not completely beyone the bounds of imagination that olfactory clues might play a role in kin recognition and also altruistic behavior. We know that some animals can recognise their young by scent. The process could go further, enabling the recognition of cousins, etc.
It is difficult to enumerate how much of human altruistic behavior is guided by kin selection, but if one was to estimate through the analysis of wills, it would seem that a large proportion of altruism is influenced by kinship. Conceivably this altruistic behavior could be influenced by olfactory cues, if only we knew enough to produce the correct ones. Such a cue would have to be tailored for the individual target.
I can imagine a world in which a target’s DNA would be acquired and analyzed, and then a pheromonal brew would be concocted that sent a strong kinship signal to that target. Conceivably it could also be accompanied by pheromones characteristic of youth, giving the olfactory impression of a long-lost, younger brother. A person sending such kinship and youth signals would be a primary candidate to benefit from altruistic behavior.