Relatives selection

Related selection ( English selection kin; also: kin selection) referred to in the evolution and Soziobiologie an extension of the theory of natural selection ( biological selection ). Within the framework of the theory of overall fitness (compare biological fitness ), the relatives selection aims to provide an explanation for the inheritance of cooperative and selfless behavior between living beings . For example, when an animal helps its relatives to raise their offspring , this promotes the survival and future dissemination of its own genetic information .

The extent of selfless behavior ( altruism ) depends on the kinship coefficient ( degree of kinship ): the closer animals are related to one another, the more selfless behavior is to be found. This fact is explained with the higher probability of allowing one's own genes to persist in subsequent generations through the help of relatives . The kin selection theory was developed by the British theoretical biologists John Maynard Smith (1964) and William D. Hamilton . But it is also called into question ( see below ).

Overall fitness

Overall fitness = direct fitness + indirect fitness

Overall genetic fitness (inclusive fitness) , the genetic success of a living being, is measured by the number of its own genes that are present in the next generation. It is made up of direct fitness, the number of genes that are passed on through one's own offspring, and indirect fitness, the number of one's own genes that are passed on to the next generation via relatives. An individual who increases the reproductive chances of a close relative can thus bring about an increase in his own overall fitness (meaning: genetic success).

This altruism is only successful and spreads in populations if the benefits for gene transmission exhibited by the altruistic behavior are greater than the costs involved ( Hamilton's rule ).

In mathematical terms, the ratio of benefits (B) to costs (C) must be greater than 1 divided by the degree of relationship .

${\ displaystyle {\ frac {B} {C}}> {\ frac {1} {r}} \ \ Leftrightarrow \ r \ cdot B> C}$

B is the benefit, C is the cost and r is the relatedness .

Taking into account the various degrees of relationship to the recipient and to one's own offspring, the following formula results (Hamilton's rule):

${\ displaystyle r_ {B} \ cdot B> r_ {C} \ cdot C}$

where is the degree of relationship of the giver to the descendants of the recipient and the degree of relationship of the giver to his own descendants. ${\ displaystyle r_ {B}}$${\ displaystyle r_ {C}}$

Examples

Example 1: An animal that does without two offspring of its own (C = 2), but instead helps a sibling (degree of relationship between siblings in diploid organisms r = 0.5) to have five additional offspring (B = 5) has one higher overall fitness than an animal that "selfishly" does not help.

${\ displaystyle r \ cdot B> C}$
${\ displaystyle 0 {,} 25 \ times 5> 0 {,} 5 \ times 2}$

Example 2: Many female workers among insect colonies forego their own offspring and even sacrifice their lives to defend the colony. The selection of relatives gives a plausible, albeit controversial, explanation. Due to the unusual haplodiploidy of hymenoptera social insects (ants, bees and wasps), full sisters of a nest have an average kinship coefficient of 0.75 - with their full brothers 0.25. However, these workers are only related to their own offspring by 50% (r = 0.5), i.e. less than to their sisters. As a result, it is genetically more advantageous for workers in social Hymenoptera to raise their own sisters than to have daughters themselves.

Example 3: If a person sacrifices his life but two siblings survive for it, it makes no difference to his genes; if he saves three siblings, his genes benefit. From an overall fitness perspective, if a person saves more than two of their children, four nephews, or eight cousins ​​by doing so, they should sacrifice their life, since a child shares 50%, a nephew 25%, and a cousin 12.5% ​​of their genes .

Group structure

The relative selection also makes statements about the group structure of populations. When does an unequal hierarchy emerge, in which only the highest ranks reproduce? To maximize their overall fitness, the individual should focus on increasing direct fitness or increasing indirect fitness depending on the environmental conditions.

If the environmental conditions are favorable and the possible reproductive success is high, then an individual should migrate and spread his genes through his own offspring. The hierarchy differences within a group are then minor.

If the environmental conditions are unfavorable and the possible reproductive success is low, then the individual should stay at home. Hierarchical group structures with a strong hierarchy then develop.

criticism

The American entomologist and sociobiologist Edward O. Wilson , who introduced the term sociobiology , has meanwhile moved away from the overall fitness theory and relative selection as the basis of sociobiology, in 2012 he even criticized this approach as unscientific. In 2013 he said about this basis of sociobiology:

“The old paradigm of social evolution, which after four decades has almost enjoyed saint status, has failed. His argument from relative selection as a process to Hamilton's inequality as a condition for cooperation to overall fitness as the Darwinian status of the colony members does not work. If relatives are selected at all in animals, then only in the case of a weak form of selection that occurs only under easily vulnerable special conditions. As the subject of general theory, overall fitness is a deceptive mathematical construct; Under no circumstances can it be conceived of as having any real biological meaning. It is also useless for reproducing the evolutionary dynamics of genetically determined social systems. "

Wilson's criticism of the overall fitness theory was contradicted by numerous scientists in various articles, for example in the journal Nature 2011 by P. Abbot, JJ Boomsma and others. a., JE Strassmann u. a., R. Ferriere and RE Michod, as well as by EA Herre and WT Wcislo.

The Price equation is a mathematically elegant synthesis of relative selection (or, more generally, individual selection, taking into account genetic relationships) and group selection , in which both individual and group selection are taken into account.