Co-operation (evolution)

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Co-operation or co-operative behaviours are terms used to describe behaviours by biological organisms which are beneficial to other members of the same species. There are several competing theories which help to explain why natural selection favours some types of co-operative behaviour. It is worth noting that more than one of the below theories can contribute to the true reason for the selection of these behaviours.

Contents 1 Kin selection 2 Reciprocity 3 The market effect 4 Multi-level selection 5 Koinophilia 6 References

[edit] Kin selection

One well accepted theory for why co-operative behaviours occur is the theory of kin selection. This theory suggests that individuals act co-operatively in order to help others which are genetically similar. Genes for such co-operative behaviour are preserved, because they help to perpetuate their own existence. The classic example is the social insects, such as bees and ants. Worker insects never reproduce, but instead, they work to allow the (genetically similar) queen to reproduce.

[edit] Reciprocity

The theory of reciprocity suggests that individuals carry out co-operative behaviours because they get something in return. In order for such behaviours to be favoured, there needs to be some perception of external physical markers that the other individual will recognise (otherwise, there is no selective pressure to maintain the behaviour). Much research about reciprocity as leading to cooperation has concentrated on the 'prisoner's dilemma' known from game theory.

[edit] The market effect

One theory suggesting a mechanism that could lead to the evolution of cooperation is the "market effect" as suggested by Noe and Hammerstein^[1]. The mechanism relies on the fact that in many situations there exists a trade off between efficiency obtaining a desired resource and the amount of resources one can actively obtain. In that case, each partner in a system could benefit from specializing in producing one specific resource and obtaining the other resource by trade. When only two partners exist, each can specialize in one resource, and trade for the other. Trading for the resource requires cooperation with the other partner and includes a process of bidding and bargaining. This mechanism can be relied to both within a species or social group and within species systems. It can also be applied to a multi-partner system, in which the owner of a resource has the power to choose its cooperation partner. This model can be applied in natural systems (examples exist in the world of apes, cleaner fish, and more). Easy for exemplifying, though, are systems from international trading. Arabic countries control vast amounts of oil, but seek technologies from western countries. These in turn are in need of Arab oil. The solution is cooperation by trade.

[edit] Multi-level selection

Multi-level selection theory suggests that selection operates on more than one level: for example, it may operate at the level of cells in the body, and then again at the whole organism level, and the community level, and the species level. Any level which is not competitive with others of the same level will be eliminated, even if the level below is highly competitive. A classic example is that of genes which prevent cancer. Cancer cells divide uncontrollably, and at the cellular level, they are very successful, because they are (in the short term) reproducing very well and outcompeting other cells in the body. However, at the whole organism level, cancer is often fatal, and so may prevent reproduction. Therefore, changes to the genome which prevent cancer (for example, by causing damaged cells to act co-operatively by destroying themselves) are favoured. Multi-level selection theory contents that similar effects can occur, for example, to cause individuals to co-operate to avoid behaviours which favour themselves short-term, but destroy the community (and their descendants) long term.

[edit] Koinophilia

Main article: Koinophilia

Definition of cooperation

Cooperation is any group behavior that benefits the individuals more than if they were to act as independent agents. There is however a second, very important, corollary to cooperation: it can always be exploited by selfish individuals who benefit even more by not taking part in the group activity, yet reaping its benefits. It is for this reason that cooperation poses an evolutionary problem. An extreme example was described by Wynne-Edwards.^[2] in 1962. He described a gannetry on Cape St Mary's on the Newfoundland coast. It consisted of two adjacent cliffs on which the gannets roosted at night. The birds that roosted on Cliff 1 mated, built nests and raised chicks. The birds that roosted on Cliff 2, despite being adult, and of both sexes, did not mate, build nests or raise chicks, unless a vacancy arose on Cliff 1. A pair of birds would then move from Cliff 2 to Cliff 1, and start breeding. The obvious benefit of this behavior was that it limited population size, thereby ensuring that everyone had enough to eat, even in the long-term. It had the additional benefit that should an epidemic or inclement weather wipe out a large portion of the colony, there were always enough spare birds to fill the vacancies created by the disaster on Cliff 1. The population could thus be restored within a very short space of time.

The evolutionary problem

This observation caused a major controversy in biological circles because it seemed evolutionarily impossible. Imagine a mutant bird on Cliff 2 which, because of its mutation, was blind to the convention that (s)he should not breed on Cliff 2. Imagine that it found a mate equally unconcerned about the convention, and that the two of them set about raising chicks either on Cliff 2, or on a convenient ledge nearby. Since this unusual behavior is due to a genetic mutation, the resultant chicks would feel equally unbound by the convention that only birds that can be accommodated on Cliff 1 may breed. Thus the grand-offspring of the first mutant pair would behave similarly, as would the great-grand-offspring. If, for ease of calculation, only half of the colony is normally accommodated on Cliff 1, then each normal bird has, on average, a 50% chance of breeding. The mutants, on the other hand, have a 100% chance of breeding. They are therefore twice as "fit" as the normal birds, meaning that the mutation will spread extremely rapidly. Within a very short space of time, it would replace its normal counterpart. In biological jargon, the normal cooperative behavior is "evolutionarily unstable"; it has no evolutionary defense against selfish mutants.

Although this is an extreme example, it illustrates the evolutionary conundrum posed by any form of cooperative behavior. The selfish individuals who do not join the hunting pack and its incumbent dangers but nevertheless share the spoils, might be only 5-10% fitter than the cooperative individuals, but that does not matter. That extra 5% fitness will eventually result in the selfish mutation replacing its cooperative counterpart. Once the mutation has taken over from the normal gene, everyone is at a disadvantage compared to the original (cooperative) condition. Though this might seem extraordinary, it is nevertheless an inevitable evolutionary trap from which there is no obvious way of escape.

Game theory solutions

The problem has been widely discussed in biology, because, despite these theoretical predictions (that cooperation is evolutionarily unstable), cooperative behavior is widespread in nature. The problem is most commonly addressed in "Game Theory" terms, which have led to important insights and understanding of cooperative behavior and how it might be evolutionarily stabilized. An example is the following. The males of many species defend and fight for territories during the mating season. If all these encounters were full scale battles, then it might turn out that, for the average male, the loss in fitness due to injuries is greater than the gains in fitness from securing a territory and therefore a mate. If this is the case, then Game Theory predicts, that inter-male squabbles should be settled through the observance of one or other non-violent convention, while reserving full scale battles only for those occasions when the convention is broken by one or other party. In other words it is tit-for tat. The convention then becomes an "Evolutionarily Stable Strategy" because the individuals who disregard the convention suffer, on average, heavier losses in fitness than the individuals who adhere to the convention.

This is indeed what is observed in nature. The rule that is most commonly followed in most species is that squabbles are settled by the convention that the current owner of the territory always wins, usually without a physical fight. This, indeed, solves the original problem, but raises a new one. If the owner always wins when challenged, then why challenge? The "game" has now degenerated into the tick-tack-toe level of pointlessness. (The Game Theory prediction is that tick-tack-toe is a game not worth pursuing as it has only one stable end-point: an endless series of draws.)

A "tit-for-tat" strategy does not always lead to pointless "games"^[3]. In some situations it confers evolutionarily stability to cooperation, unless a player makes a mistake (e.g. mistakenly rewards cooperation with a selfish response), in which case a long series of selfish tit-for-tat acts ensues, which can only be broken by a second mistake (e.g. a cooperative response to a selfish act) ^[4]. Different variations, however, on the tit-for-tat theme^{[5] [6]} can outperform pure tit-for-tat, and therefore take over from it, but some are, in turn, unstable in the presence of selfishness. Thus, if the different strategies arise by random mutations, then the affected population will cycle through all of the strategies in an endless series of chaotic cycles^[7]. Game Theory, on its own, therefore does not seem to provide an answer to why cooperation is as common as it is (and apparently evolutionarily stable). It certainly does not provide an explanation as to why Wynne-Edwards' gannets behaved the way he observed them to behave.

Koinophilia

Koinophilia provides a simple and obvious explanation for the evolutionary stability of all forms of cooperative behavior, including the observance of rituals and conventions. Since, by definition, fit traits replace less fit traits, each fit trait tends to become more common, and ultimately the dominant phenotype, while the maladaptive traits become increasingly rare. Sexual creatures would therefore be expected to prefer mates sporting predominantly common features, while avoiding mates with unusual or unfamiliar attributes. This is termed koinophilia^[8]. It causes common features to become more common still, and at a rate that exceeds that which would be driven by natural selection alone. Since it affects the entire external phenotype, it will include behavior.

Because koinophilia discriminates against any rare or unusual form of behavior it is capable of stabilizing any strategy in any of the cooperation versus selfishness games. Any individual who behaves abnormally (as a result of a mutation, or through immigration) will not easily find a mate, and will thus not be able to pass that mutation on into the next generation. Koinophilia therefore has the effect of increasing the fitness of whatever happens to be the common strategy^[5]. Different groups, practicing different strategies will thus become evolutionarily trapped in these different behaviors. A group that happens, by chance, to follow a cooperative strategy will, by definition, be fitter, as a group, than groups that consist of selfish individuals. Competition between such groups will ultimately result in the replacement of the selfish groups by cooperative groups^[9]. Thus, Wynne-Edwards' gannets can be expected to continue practicing population control well into the future, without fear of being driven into extinction by selfishly reproducing mutants, because those mutants will experience difficulties in finding mates. And, even if one of them did happen to find a mate, then the offspring would be discriminated against, as their behavior would still stand out as being unusual, or deviant, in a large colony of several hundred birds.

[edit] References

• Mikhail Burtsev and Peter Turchin: Evolution of cooperative strategies from first principles, Nature 440, 1041-1044 (20 April 2006)

Topics in evolutionary ecology v • d • e
Patterns of evolution: Convergent evolution • Evolutionary relay • Parallel evolution
Colour and shape: Aposematism • Mimicry • Crypsis
Interactions between species: Mutualism • Cooperation • Predation • Parasitism