A great many biologists doubt that group selection could be sufficiently effective to enable the formation of altruistic behaviour. They base their considerations on the assumption that the structure and dynamics of the population in most species of organisms substantially favour individual selection overgroup selection. Thus, altruistic individuals should be rapidly eliminated in every case in competition with selfish individuals (Williams 1966).
At the present time, biologists mostly assume that a major part of altruistic behaviour that we encounter in nature was formed by kin selection (selection amongst related clans) and is thus primarily intended to assist the close relatives of the altruistic individual. As discussed in the part devoted to inclusive fitness (I.10.2), an organism can increase its evolutionary success in two ways. It can attempt to produce the greatest possible number of its own progeny or it can assist in producing the greatest number of the progeny of its relatives, i.e. individuals with which it has a great many common genes. Thus, if a certain pattern of behaviour improves the chances of survival of one’s own young, siblings, progeny of siblings or other close relatives, this is a pattern of behaviour that is almost as selectionally advantageous as the pattern that increases the chances of survival of the organism itself. Basically, individuals do not compete together, but rather individual families (genuses, related clans) of mutually more or less related individuals. However, the effectiveness of kin selection depends not only on the ratio of the costs and benefits (from the standpoint of biological fitness) of altruistic behaviour and on the relatedness of mutually assisting individuals, but on the relative importance of competition for resources between relatives. If sufficiently effective dispersion of the related individuals does not occur in the given species, then the main competitors for all the resources will be related individuals and any advantage of altruistic behaviour in relation to related individuals will be lost (West, Pen, & Griffin 2002).
A number of models have been published since the beginning of the 1980’s (Wilson 1983; van Baalen & Rand 1998; Day & Taylor 1998), indicating that fixation of altruistic behaviour can occur in a great many situations even by classical group selection in which mutually unrelated individuals assist one another, and groups with these altruists prosper better than groups with selfish individuals. The degree to which group selection, now frequently denoted interdemic selection or kin selection, predominates in the formation of a certain pattern of altruistic behaviour, probably depends in each particular case on the structure and dynamics of the population of the particular species (Shanahan 1998). If, for example, a flock is formed by a group of mutually related individuals in each case, e.g. the progeny of a single nesting pair, then a substantial effect of kin selection can be expected. If a flock is formed at the beginning of each season by mutually unrelated individuals and again disintegrates at the end of each season, a substantial effect of classical group selection can be expected. Various types of selection can, of course, act simultaneously in real situations.
- more or less8150
- not at all4402