THE COMMONALITY OF GENES AND THE CONCEPTS OF ALTRUISM

The system controlling any behaviour develops in the individual as a consequence of interactions between the genotype and its environment. Hence it is of value to consider how genes might influence behaviour and to consider how a gene which does so might have spread in the population. Those who have sought to explain altruistic behaviour towards close relatives have found it useful to consider degrees of relatedness because these would allow estimation of the likelihood that a gene which promoted altruistic behaviour would be shared with the individual who benefitted from the act. Hamilton (1963, 1964a, b) referred to degrees of relatedness such as 0.5 between parents and offspring and between siblings and 0.25 between grandparents and grandchildren. However, other authors sometimes made the assumption that degree of relatedness could be translated directly to the number of genes in common. Alexander (1979, p. 45) said ‘full siblings on average have 50% of their genes in common’ and Barash (1979, p. 134) referring to bees with haploid reproductive males said ‘each worker shared three quarters of its genes with its sisters’. However, as Broom (1981, p. 10) explained: