Sexual Selection and Mate Choice

Herbert Spencer first coined the phrase survival of the fittest in 1864, to describe Darwin's observations of natural selection. One way to quantify the fitness of an individual is in the number of offspring that it can contribute to the next generation - so an organism can improve its fitness by producing more offspring that are then able to successfully reproduce themselves. Reproduction is a critical element of fitness, and sexually-reproducing organisms must mate in order to pass their genes on to the next generation. This means that for sexually-reproducing organisms, competing for mates becomes a key part of fitness.

This pressure to find a mate leads to a phenomenon known as sexual selection - a type of selection that acts upon traits associated with mating and courtship. Typically, sexual selection is more intense for the sex that invests the least amount of energy in reproduction. Since sperm is energetically inexpensive to produce, males generally bear the brunt of sexual selection pressures. Conversely, eggs are energetically expensive to produce and then gestate. This means that females are expected to be more selective when choosing mates, and males must invest substan