The study of animal cognition has provided valuable data throughout the years, yet its reliance on laboratory work leaves some open questions. The main question is whether animals employ cognition in daily decision-making. The following discussion uses sperm competition (SC) as a test case for demonstrating the effect of cognition on routine choices, in this case, sexual selection. Cognition is...

A small marsupial has thrown new light on the question of why females typically mate with several males: promiscuous female antechinuses have many more surviving offspring because males that are successful in sperm competition also sire healthy offspring.

We explored aspects of men's and women's short-term sexual psychology as a function of a potential short-term partner's relationship status. A total of 209 men and 288 women reported how likely they would be to pursue a casual sexual relationship with an attractive member of the opposite sex who was (1) married, (2) not married but has casual sexual partners, or (3) not married and has no casua...

Sperm competition has led to spectacular adaptations in males and their ejaculates. A recent study of Tanganykan cichlids provides compelling evidence that sperm competition can drive the evolution of faster, longer sperm.

Most discussions of ‘sperm competition’ have ignored the potential for competition among the different sperm genotypes present in the ejaculate of a single male. Rivalry within ejaculates may limit cooperation among the members of an ejaculate when they compete with sperm produced by other males. A gene that gains an advantage in competition within an ejaculate (a segregation distorter) may inc...

Love darts are hard 'needles' that many snails and slugs use to pierce their partner during mating. In a few species, darts have been shown to play a role in sperm competition. Two new papers, by Davison et al., and Koene and Schulenburg, might further pique researchers' interest, because they show how the full potential of darts can be tapped for studies of sexual selection in hermaphrodites.

Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the...

Sperm competition is widely recognized as a potent force in evolution, influencing male behavior, morphology, and physiology. Recent game theory analyses have examined how sperm competition can influence the evolution of ejaculate expenditure by males and the morphology of sperm contained within ejaculates. Theoretical analyses rest on the assumption that there is sufficient genetic variance in...

Nonhuman males attend to the number of potential sexual rivals in the local environment to assess sperm competition risk. Males of these species sometimes perform more frequent in-pair copulations to increase the likelihood of success in sperm competition. Here, we extend this research to humans, Homo sapiens. We secured self-report data from 393 men in a committed, sexual, heterosexual relatio...