Sexual Selection
Darwin considered traits selected according to their role in mating to be
separate from those acted on by natural selection. He considered this a
different type of selection that he called "sexual selection." Sexual
selection occurs in two ways: through contests and through choice.
Contest
Contests are competitions between members of the same sex for access to the
other sex. This competition may take many different forms. A common example is
direct combat between males. These fights may determine hierarchies in which
the dominant males get first access to sexually receptive females or to
establish territories, whose resources help attract females. In cases like
these, horns, antlers, or other combative devices are acted upon by sexual
selection because they are directly involved in helping an individual obtain a
mate.
Choice
While contests involve direct physical competition between members of the same
sex, choice involves competition for attention from the opposite sex. For
example, the tail feathers of the peacock are a sexually selected trait, but
they are not used to attack or fend off other males. Instead, they are intended
to attract peahens. The peahens can use such showy displays as an indicator of
a male's quality or fitness, because the male has been able to survive even
with the added cost of an otherwise useless and sometimes dangerously
conspicuous display. Signaling displays such as the peacock's tail are
discussed further in the Signaling and Communication
SparkNote of animal
behavior.
