XIV.8 Members of a single species compete on an intersexual and intrasexual level; the evolutionary outcome of this competition can be estimated using game theory

The driving force for evolution need not always be only selection following from intraspecies competition for the greatest resistance to pressures from the external environment and the best utilization of the resources that this external environment provides. In evolution, selection following from intraspecies competition can even lead to the formation of adaptations, structures and patterns of behavior that permit the organism to obtain advantages at the expense of the other members of the particular biological species and population and, simultaneously, of course, adaptations that allow individuals to prevent similar efforts on the part of the other members of the population.Thus, a constant evolutionary battle occurs amongst the members of a single species, in which individuals utilize variousstrategies which are intended to allow them to gain a certain advantage at the expense of the rest.

            Some of the aspects of this evolutionary game can best be illustrated on the example of intraspecies competition in animals that most frequently have a rather familiar and therefore easily understandable form of competition of various patterns of behavior.However, similar evolutionary games also take place between plants and viruses; however, there they take the form of competition in the creation of various morphological or biochemical structures rather than various patterns of behavior.

            In the following text, we will be concerned with the progress of such evolutionary games only on examples of competition of various patterns of behavior in animals.However, such an approach has certain drawbacks.If people compete together (for example play chess, football or shoot ballistic rockets at one another), they consciously choose a strategy, mostly from a number of strategic alternatives.Simultaneously, they usually know the goal that they want to achieve and also know the probable effects of the chosen strategy on their competitors and teammates.It cannot be excluded that a similar view into the rules and progress of the battle is also valid to a certain degree amongst some animals (see XVII.3.1).However, it is rather improbable and, especially, uninteresting from an evolutionary standpoint.In evolution, traits, here patterns of behavior, are of importance if they are determined genetically and are thus heritable.Thus, if we state that a female must try to force a male to invest the greatest possible amount of energy into building a nest in the precopulation phase of reproduction, then we are using our anthropomorphic terminology.If we wanted to avoid this at any cost, we would have to say:“Only those females will remain permanently in the population that carry a gene or genes that directly or frequently indirectly affect their behavior in a manner such that  they will reproduced with those males that have, in their genome, a gene or genes that directly or frequently indirectly affect their behavior in a manner such that, in the precopulation phase, they will invest great efforts in the construction of a nest.”

            If we compare the length and comprehensibility of the two sentences, the comparison will most certainly favor the anthropomorphic terminology.However, the use of this terminology is simultaneously somewhat misleading; in the absence of appropriate emphasis to the contrary, it could create the impression in the reader that the strategy is chosen by individuals in the same way as in people, i.e. on the basis of free choice.It must again be emphasized that, whatever the terminology or strategy being discussed in evolutionary biology, the individual organisms do not choose voluntarily or consciously, that they simply behave as dictated directly or indirectly by their genes.Most individuals do not use a certain strategy because it will probably be successful. Rather, because this certain strategy has already been successful, the population contains a predominance of individuals that use it.

            Here, it should be recalled that it makes no sense to attempt to evaluate the evolutionary strategy of organisms from ethical viewpoints or, to the contrary, look for justification for some form of human behavior in the evolutionary laws of intraspecies competition.The laws of ethics do not make any sense amongst animals; in human society, they should, to the contrary, be preferred over biological laws in all cases.

            In gonochorists, the individuals within the species have been differentiated into males and females.The two sexes differ in a number of traits and each has its specific role in the biology of the species.As a consequence of this division of roles, the strategies that the members of one or the other sex can use to gain an advantage at the expense of the other members of the particular species also differ.We can best understand the concept that the members of one sex can attempt to gain an advantage at the expense of members of the other sex.And this is actually frequently the case.However, it should always be recalled that a similar and usually much more intense battle for gaining advantages at the expense of another individual also occurs constantly amongst the members of the same sex.

            The course and evolutionary consequences of intersexual and intrasexual competition, similar to the course and consequences of the competition of any alternative game strategies can be estimated using the mathematical discipline, game theory (see IV.5.1 and XVI.5).For example, game theory can be used to determine the optimum strategy for males and females and the results of intersexual competition.We can also determine what is evolutionarily stable strategy (ESS) in the given case (see IV.5.1).The optimum strategy and evolutionarily stable strategy need not be identical.In more complicated games, where there is a predefined role of the competitors and teammates, the optimum game strategy can be considered to be the strategy that brings the teammates the greatest advantage at the expense of the competitors, for example the maximum average reproduction success of males at the expense of females.In contrast, evolutionarily stable strategy is strategy that, when it predominates in the population, permits gaining the maximum advantage at the expense of teammates, here members of the same sex, following any other (minority) game strategy.

            The following text will be concerned primarily with competition between members of different sexes, intersexual competition.The best known manifestations of competition between members of the same sex, intrasexual competition for sex partners, i.e. sexual selection, will be discussed in a separate chapter (XV).

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.