Sexual Signals as Advertisers of Resistance to Mistakes

To be evolutionarily stable, sexual signals need to convey information regarding the quality or motivation of individuals. This can be achieved through direct or indirect signal costs that guarantee honest communication or through signal designs that facilitate the assessment of quality. Here, I present the case for an alternative hypothesis: that signalling exposes informative mistakes. Signalling mistakes range from occasional to frequent and from slight distortions of typical signals to grossly atypical signals. Their occurrence may be enhanced by disease or stress, thus revealing individual quality or motivation, and receivers typically respond negatively to them. By this mechanism, honest communication is due to costs of developing resistance to mistakes. Therefore, the hypothesis can function independently of signal design costs, although it can also be enhanced by signal design costs when those increase the occurrence of mistakes. This hypothesis widens the scope of signals expected to be sexually selected and creates new approaches to research in sexual selection and animal communication.     

Mistakes can stabilise the dynamics of rock-paper-scissors games

A game of rock-paper-scissors is an interesting example of an interaction where none of the pure strategies strictly dominates all others, leading to a cyclic pattern. In this work, we consider an unstable version of rock-paper-scissors dynamics and allow individuals to make behavioural mistakes during the strategy execution. We show that such an assumption can break a cyclic relationship leading to a stable equilibrium emerging with only one strategy surviving. We consider two cases: completely random mistakes when individuals have no bias towards any strategy and a general form of mistakes. Then, we determine conditions for a strategy to dominate all other strategies. However, given that individuals who adopt a dominating strategy are still prone to behavioural mistakes in the observed behaviour, we may still observe extinct strategies. That is, behavioural mistakes in strategy execution stabilise evolutionary dynamics leading to an evolutionary stable and, potentially, mixed co-existence equilibrium.     

Mistakes in diagnosing non-accidental injury: 10 years' experience

Fifty children who were referred to the child abuse team in Leeds over the 10 years 1976-86 with suspected non-accidental injury were found to have conditions which mimicked non-accidental injury. These included impetigo (nine children) and blue spots (five children). Five children who presented with multiple bruising had haemostatic disorders. Eight children had disorders of the bone. Five children had been previously abused physically. Four showed evidence of neglect. One had evidence of non-accidental injury as well as the condition mimicking abuse.It is emphasised that when child abuse is suspected a sensitive and thorough assessment should be carried out by a paediatrician who is experienced in this.     

Mistakes allow evolutionary stability in the repeated prisoner's dilemma game

The repeated prisoner's dilemma game has been widely used in analyses of the evolution of reciprocal altruism. Recently it was shown that no pure strategy could be evolutionarily stable in the repeated prisoner's dilemma. Here I show that if there is always some probability that individuals will make a mistake, then a pure strategy can be evolutionarily stable provided that it is "strong perfect equilibria" against itself. To be a strong perfect equilibrium against itself, a strategy must be the best response to itself after every possible sequence of behavior. I show that both unconditional defection and a modified version of tit-for-tat have this property.     

Misplaced Paternalism and other Mistakes in the Debate over Kidney Sales

Erik Malmqvist defends the prohibition on kidney sales as a justifiable measure to protect individuals from harms they have not autonomously chosen. This appeal to ‘group soft paternalism’ requires that three conditions be met. It must be shown that some vendors will be harmed, that some will be subject to undue pressure to vend, and that we cannot feasibly distinguish between the autonomous and the non‐autonomous. I argue that Malmqvist fails to demonstrate that any of these conditions are likely to obtain. His argument involves two common errors. First, he, like many, proceeds on a mistaken understanding of how to assess harm. What matters is not the balance of costs and benefits of vending, but a comparison of potential vendors’ welfare across two possible courses of action. Second, Malmqvist's concerns about third‐party pressure are predicated on an empirically unrealistic understanding of the operation of a regulated market. A widely underappreciated fact is that kidney sales will be relatively rare, and most who try to vend will be unable to. Because pressure on another to vend will not result in the desired outcome, few will exert it.