What are the targets of natural selection remains a controversial issue in Biology. Here I propose the "Extended Fitness" hypothesis, in which extended phenotypes emerge as a link between individual and group selection. The basic premise of the extended fitness hypothesis is that extended phenotypes can be used by members of the same group since they are adapted to use them. Thus, extended phen...

This paper explores adverse selection in the voluntary and compulsory individual annuity markets in the United Kingdom. Two empirical regularities support standard models of adverse selection. First, annuitants are longer-lived than non-annuitants. These mortality differences are more pronounced in the voluntary than in the compulsory annuity market. We estimate that the amount of adverse selec...

The idea of evolutionary game theory is to relate the payoff of a game to reproductive success (= fitness). An underlying assumption in most models is that fitness is a linear function of the payoff. For stochastic evolutionary dynamics in finite populations, this leads to analytical results in the limit of weak selection, where the game has a small effect on overall fitness. But this linear fu...

We develop a model of selection that incorporates a key element of recent health reforms: an individual mandate. Using data from Massachusetts, we estimate the parameters of the model. In the individual market for health insurance, we find that premiums and average costs decreased significantly in response to the individual mandate. We find an annual welfare gain of 4.1% per person or $51.1 mil...

The number of different major histocompatibility (MHC) molecules expressed per individual is widely believed to represent a trade-off between maximizing the detection of foreign antigens, and minimizing the loss of T cell clones due to self-tolerance induction. Using a mathematical model we here show that this argument fails to explain why individuals typically express of the order of 1020 diff...

The imprint of natural selection on protein coding genes is often difficult to identify because selection is frequently transient or episodic, i.e. it affects only a subset of lineages. Existing computational techniques, which are designed to identify sites subject to pervasive selection, may fail to recognize sites where selection is episodic: a large proportion of positively selected sites. W...

The present study examined the moderating role of social support and challenging behaviour on the stress-physical health relationship in parents caring for children with intellectual disabilities. Parents of children with intellectual disabilities (n = 70) reported more physical health problems compared to control parents (n = 45) and were more likely to visit their general practitioner. Furthe...

This study investigated the economics of multisystemic therapy (MST) versus individual therapy (IT) using rearrest data from a 13.7-year follow-up (Schaeffer & Borduin, 2005) of a randomized clinical trial with serious juvenile offenders (Borduin et al., 1995). Two types of benefits of MST were evaluated: The value to taxpayers was derived from measures of criminal justice system expenses (e.g....

This article examined the long-term effects of multisystemic therapy (MST) vs. individual therapy (IT) on the prevention of criminal behavior and violent offending among 176 juvenile offenders at high risk for committing additional serious crimes. Results from multiagent, multimethod assessment batteries conducted before and after treatment showed that MST was more effective than IT in improvin...

How can collective action evolve when individuals benefit from cooperation regardless of whether they pay its participation costs? According to one influential perspective, collective action problems are common, especially when groups are large, but may be solved when individuals who have more to gain from the collective good or can produce it at low costs provide it to others as a byproduct. S...