The evolution of parental investment: re-examining the anisogamy argument.

In most animals with internal fertilization, the early costs of parenting by necessity falls on the female, whereas male and female investments are closer substitutes later on. After Dawkins and Carlisle's (1976) critique of Trivers' (1972) anisogamy argument, the conventional wisdom has been that early investment costs as such are irrelevant for the allocation of subsequent parental investment. However, in a stylized evolutionary model with recurrent mutations, we show that if only one parent bears early costs, then the other parent should bear a substantial fraction of later costs.

A randomized trial of the effect of testosterone and estrogen on verbal fluency, verbal memory, and spatial ability in healthy postmenopausal women.

Objective: To test the causal relationship between sex hormones and cognitive skills in postmenopausal women. We hypothesized that testosterone would decrease verbal memory and verbal fluency and increase spatial ability compared with a placebo. For estrogen, we conversely hypothesized that the treatment would increase verbal fluency and verbal memory and decrease spatial ability.

Positive interactions promote public cooperation.

The public goods game is the classic laboratory paradigm for studying collective action problems. Each participant chooses how much to contribute to a common pool that returns benefits to all participants equally. The ideal outcome occurs if everybody contributes the maximum amount, but the self-interested strategy is not to contribute anything.

A randomized trial of the effect of estrogen and testosterone on economic behavior.

Existing correlative evidence suggests that sex hormones may affect economic behavior such as risk taking and reciprocal fairness. To test this hypothesis we conducted a double-blind randomized study. Two-hundred healthy postmenopausal women aged 50-65 years were randomly allocated to 4 weeks of treatment with estrogen, testosterone, or placebo.