Altruism: Evolution and a Repercussion

Evolutionary biologists have developed a powerful theory of the evolutionary foundations of altruism between relatives. The theory is based on the idea that individuals who are related by blood share genes. Consider a gene that governs a particular behaviour. The likelihood that the gene will be replicated is higher when the gene takes into account not only the extra reproductive opportunities that the behaviour confers on the host who carries the gene, but also the extra reproductive opportunities that the behaviour confers on relatives of the host who also carry the gene. William Hamilton, the pioneer of this theory, describes it as follows: The social behaviour of a species evolves in such a way that in each distinct behavior-evoking situation the individual will seem to value his neighbor’s fitness against his own according to the coefficients of relationship appropriate to that situation. (Hamilton, 1964: 19) The coefficient of relationship between to individuals is the probability that a randomly selected gene in one of these individuals will have an exact copy located in the other individual as a result of descent from a common ancestor. In the case of a haploid population in which each parent has a single gene for being altruistic or selfish and matting is monogamous, the coefficient of relationship between to siblings is ½. ‘Hamiltons’s rule’ is that altruism will spread in a population if the benefit obtained from giving multiplied by the coefficient of relationship exceeds the cost of giving.