Now for the application. In good times in the history of a species, when everything is prosperous, external conditions are favorable, and food is abundant, females are in excess, and individuals are greatly multiplied. Under these conditions, evolution would be slow and uniform. But in _bad_ times in the history of a species, when external conditions were unfavorable, not only would there be excess of males, but these, through the influence of the changing environment, as well as through the dominance of the male element, would be more than usually varied in character. Among the strongly divergent varieties thus formed, the fittest--i. e., those most in accord with the changing environment--would survive and leave offspring partaking of their character. We have already repeatedly said that the severer pressure of a rapidly-changing environment determines correspondingly rapid changes in organic forms. It may do so in many ways; but, according to Brooks, one of the most important ways is by determining an excess of the male element. In brief, then, the causes of rarity of transitional forms among fossils are--1. The change being, for the reasons given, comparatively rapid, the _number of generations_ between consecutive species are few, perhaps only one. 2. Times of rapid change are also times of unfavorable conditions, and therefore the number of _individuals_ in each generation is small, and all the smaller--in Brooks’s view--because of the fewness of females. When we remember that fossils are but a small fraction of the actual faunas and floras of the time, surely these two causes go far toward explaining the rarity of links between _species_. 3. Add to these the existence of periods of wide-spread changes in physical geography and climate, and consequent wide migrations and dispersals of species, and we sufficiently account for those sweeping changes in species, genera, families, and orders, which mark the limits of the great eras, and which are made still more abrupt, and apparently supernatural, by the loss of record at these times.[38] =Objection.=--There is still one more objection which will be made. We have drawings of plants, animals, and men, by Egyptian artists, who lived at least three thousand years ago, and the species of the one and the races of the other are still the same. Still better, we have among the wrappings of Egyptian mummies the very plants themselves, leaves and flowers perfectly preserved, and even colors almost perfect. Yet the species are exactly the same as grow in Egypt to-day. If species are made by gradual transmutation, surely there ought to have been some change in three thousand years.