Charles Darwin & Sexual Selection

Here, in his own words, Darwin’s observations of differences between the sexes that led to his hypothesis of sexual selection:

In the several great classes of the animal kingdom - in mammals, birds, reptiles, fishes, insects, and even crustaceans - the differences between the sexes follow nearly the same rules. The males are almost always the wooers; and they alone are armed with special weapons for fighting with their rivals. They are generally stronger and larger than the females, and are endowed with the requisite qualities of courage and pugnacity. They are ornamented with infinitely diversified appendages, and with the most brilliant or conspicuous colours, often arranged in elegant patterns, whilst the females are unadorned. These various structures for charming or securing the female are often developed in the male during only part of the year, namely the breeding-season.

Photo credit: http://www.crbs.umd.edu/crossingborders/ai2008/lessonplans08.html