Mate choice is one of two components of sexual selection, the other being intrasexual selection.Ideas on sexual selection were first introduced in 1871, by Charles Darwin, then expanded on by Ronald Fisher in 1915.In systems where mate choice exists, one sex is competitive with same-sex members Charles Darwin first expressed his ideas on sexual selection and mate choice in his book The Descent of Man, and Selection in Relation to Sex in 1871.

Direct sex-16

This became known as Bateman's principle, and although this was a major finding that added to the work of Darwin and Fisher, it was overlooked until George C.

Williams emphasised its importance in the 1960's and 1970's.

At present, there are five mechanisms that explain how mate choice has evolved over time.

These are direct phenotypic benefits, sensory bias, the Fisherian runaway hypothesis, indicator traits and genetic compatibility.

There is much support for maintenance of mate choice by direct benefits Indirect benefits increase genetic fitness for the offspring, and thereby increase the parents' inclusive fitness.

When it appears that the choosy sex does not receive direct benefits from his or her mate, indirect benefits may be the payoff for being selective.

Darwin proposed two explanations for the existence of such traits: these traits are useful in male-male combat or they are preferred by females. Darwin treated natural selection and sexual selection as two different topics, although in the 1930's biologists defined sexual selection as being a part of natural selection.

Fifteen years later, he expanded this theory in a book called The Genetical Theory of Natural Selection.

In 1972, soon after Williams' revival of the subject, Robert L. Trivers defined parental investment as any investment made by the parent that benefits his or her current offspring at the cost of investment in future offspring.

These investments include the costs of producing gametes as well as any other care or efforts that parents provide after birth or hatching.

Being choosy (having a bias in the context of mating) must incur a fitness advantage in order for this behaviour to evolve.