Sexual selection for males with beneficial mutations.

Sexual selection is the process by which traits providing a mating advantage are favoured. Theoretical treatments of the evolution of sex by sexual selection propose that it operates by reducing the load of deleterious mutations. Here, we postulate instead that sexual selection primarily acts through females preferentially mating with males carrying beneficial mutations.

The psychological foundations of reputation-based cooperation.

Humans care about having a positive reputation, which may prompt them to help in scenarios where the return benefits are not obvious. Various game-theoretical models support the hypothesis that concern for reputation may stabilize cooperation beyond kin, pairs or small groups. However, such models are not explicit about the underlying psychological mechanisms that support reputation-based cooperation.

Cooperating to show that you care: costly helping as an honest signal of fitness interdependence.

Social organisms often need to know how much to trust others to cooperate. Organisms can expect cooperation from another organism that depends on them (i.e.

The benefits of being seen to help others: indirect reciprocity and reputation-based partner choice.

When one individual helps another, it benefits the recipient and may also gain a reputation for being cooperative. This may induce others to favour the helper in subsequent interactions, so investing in being seen to help others may be adaptive. The best-known mechanism for this is indirect reciprocity (IR), in which the profit comes from an observer who pays a cost to benefit the original helper.

Cooperation: How Vampire Bats Build Reciprocal Relationships.

In theory, reciprocal relationships should develop gradually, to reduce the risk of helpers being exploited. In a classic case of reciprocity, vampire bats share blood with starving roost-mates. Now it transpires they share food only after first having established grooming relationships.

Prosocial behavior as sexual signaling.

Maestripieri et al. provide an important service in highlighting prosocial biases toward attractive people from a cross-disciplinary perspective. Here I comment on the conceptual and critical side of their review of evolutionary psychology studies.

Partner Choice Drives the Evolution of Cooperation via Indirect Reciprocity.

Indirect reciprocity potentially provides an important means for generating cooperation based on helping those who help others. However, the use of 'image scores' to summarize individuals' past behaviour presents a dilemma: individuals withholding help from those of low image score harm their own reputation, yet giving to defectors erodes cooperation. Explaining how indirect reciprocity could evolve has therefore remained problematic.

Human cooperation: the race to give.

An analysis of online charity donations reveals that, when males make large donations to attractive female fundraisers, other males respond in kind, providing field evidence for 'competitive altruism' in which helpful acts are used as a display to attract partners.

When punishment pays.

Explaining cooperation in groups remains a key problem because reciprocity breaks down between more than two. Punishing individuals who contribute little provides a potential answer but changes the dilemma to why pay the costs of punishing which, like cooperation itself, provides a public good. Nevertheless, people are observed to punish others in behavioural economic games, posing a problem for existing theory which highlights the difficulty in explaining the spread and persistence of punishment.

Competitive morality.

Baumard et al. argue that partner choice leads to fairness and mutualism, which then form the basis for morality. I comment that mutualism takes us only so far, and I apply the theory of competitive altruism in arguing how strategic investment in behaviours which make one a desirable partner may drive moral conduct.

Inclusive fitness theory and eusociality.

Arising from M. A. Nowak, C.

Cooperators benefit through reputation-based partner choice in economic games.

Explaining unconditional cooperation, such as donations to charities or contributions to public goods, continues to present a problem. One possibility is that cooperation can pay through developing a reputation that makes one more likely to be chosen for a profitable cooperative partnership, a process termed competitive altruism (CA) or reputation-based partner choice. Here, we show, to our knowledge, for the first time, that investing in a cooperative reputation can bring net benefits through access to more cooperative partners.

Evolutionary stable investment in products that confer both an individual benefit and a public good.

Why should a microbe manufacture extracellular enzymes if its competitors can free-ride on these enzymes? Similarly, why should an animal place seeds into storage when others can exploit this stored resource? A solution to this general class of problems becomes apparent if one assumes that investors directly benefit from a proportion of the investments they make. Thus, when individuals benefit from a proportion p of their investments, but share the rest with other individuals in the system, then an evolutionarily stable level of investment can evolve which is higher the higher the value of p. These evolutionarily stable investment points mark the junction at which several classical games meet, so that changes in investment can move interactions from one game type to another.

Environmental adversity and uncertainty favour cooperation.

Background: A major cornerstone of evolutionary biology theory is the explanation of the emergence of cooperation in communities of selfish individuals. There is an unexplained tendency in the plant and animal world - with examples from alpine plants, worms, fish, mole-rats, monkeys and humans - for cooperation to flourish where the environment is more adverse (harsher) or more unpredictable.

Results: Using mathematical arguments and computer simulations we show that in more adverse environments individuals perceive their resources to be more unpredictable, and that this unpredictability favours cooperation.

Evolution of direct and indirect reciprocity.

Indirect reciprocity (IR) occurs when individuals help those who help others. It is important as a potential explanation for why people might develop cooperative reputations. However, previous models of IR are based on the assumption that individuals never meet again.

Cues of being watched enhance cooperation in a real-world setting.

We examined the effect of an image of a pair of eyes on contributions to an honesty box used to collect money for drinks in a university coffee room. People paid nearly three times as much for their drinks when eyes were displayed rather than a control image. This finding provides the first evidence from a naturalistic setting of the importance of cues of being watched, and hence reputational concerns, on human cooperative behaviour.

The development of cooperative relationships: an experiment.

Pairs of individuals frequently face situations in which they could do well if they cooperated, but each risks being exploited. The Prisoner's Dilemma is widely used for investigating such scenarios, but it is framed in terms of cooperating and defecting, whereas in reality cooperation is rarely "all or nothing". Recent models allowing for variable investment in cooperation indicated the success of a strategy of "raising-the-stakes" (RTS), which invests minimally at first and then increases its investment if its partner matches it.

Behaviorial evolution: does similarity breed cooperation?

Reciprocity, whether direct or indirect, is thought to be the key to establishing cooperation among non-relatives. But Riolo et al. have presented a model in which cooperation is instead based on similarity: agents donate only when their partner's 'tag' lies within a 'tolerance' range around their own.

The stability of cooperation involving variable investment.

In this paper, we attempt to reconcile the results of several studies which have investigated the evolution of cooperation between non-relatives in systems where investment in partners can vary. In contrast to previous proposals, we show for the first time that variable-investment cooperation can be readily maintained in inter-species mutualistic relationships even in the absence of spatial structure, but that the stability of this interaction is dependent on the particular investment-response rule that is employed. By allowing the evolution of investment-response parameters in both inter- and intra-specific versions of the continuous variable-investment Prisoners' Dilemma we show that, in the absence of further factors, the raise-the stakes (RTS) strategy is likely to evolve into a simpler, variable investment form of Give-as-Good-as-you-Get that initially offers a high fixed amount and subsequently matches its partner's investment.