Varieties merge gradually into species. Animals tend to increase in geometrical ratio. Varieties diverge in consonance with diversity of opportunity for life. In the struggle for existence those which best accord with their surroundings will survive and propagate their kind. Sexual selection has put a premium on beauty. The causes which in brief periods produce varieties, in long periods give rise to species. Instincts, as of the hive bee, are slowly developed. Geology supports the theory of Evolution: the changes in time in the fossil record are gradual. Geographical distribution lends its corroboration: in each region most of the inhabitants in every great class are plainly related. A common ancestor is suggested when we see the similarity of hand, wing and fin. Embryos of birds, reptiles and fish are closely similar and unlike adult forms. Slight changes in the course of millions of years produce wide divergences.

During his voyage on the Beagle Darwin saw fossil armadillos like existing species, and on the islands of the Galapagos group a gradually increased diversity of species of every kind. All this suggested that species gradually become modified. Notes gathered of facts bearing on the question. Observes that it is the variation between one animal and another which gives the breeder his opportunity. Reads Malthus on Population, a work which points out the keen struggle for existence and that favourable variations tend to be preserved. In 1842 draws up a brief abstract of the theory of “natural selection.” In 1856 begins an elaborate work on the same theme, but in 1858, hearing that Wallace has written an essay advancing an independent theory of natural selection, offers a summary of his argument to the Linnean Society of London. Writes “The Origin of Species,” which is published most successfully, November, 1859.

Since evolution is probable for all other animals, it is probable for man. The human form has so much in common with the forms of other animals that community of descent is strongly suggested. Man, like other creatures, is subject to the struggle for existence. Evidence shows that it is likely that man is descended from a tailed and hairy quadruped that dwelt in trees. Man's mental power has been the chief factor in his advance, especially in his development of language. Conscience is due to social instincts, love of approbation, memory, imagination and religious feeling. Sexual selection in its effects upon human advancement.

The colours of animals are useful for concealment from their prey, from the creatures upon which they prey. The lion is scarcely visible as he crouches on the sand or among desert rocks and stones. Larks, quails and many other birds are so tinted and mottled that their detection is difficult. The polar bear, living amid ice and snow, is white. Reptiles and fish are so coloured as to be almost invisible in the grass or gravel where they rest. Many beetles and other insects are so like the leaves or bark on which they feed that when motionless they cannot be discerned. Some butterflies resemble dead, dry or decaying leaves so closely as to elude discovery. Every individual better protected by colour than others, has a better chance for life, and of transmitting his hues. Harmless beetles and flies are so like wasps and bees as to be left alone.

The hoof of the horse is simply a greatly enlarged and thickened nail: four of his five toes are reduced to mere vestiges. His teeth are built of substances of varying hardness: they wear away at different rates presenting uneven grinding surfaces. Probable descent of the horse, link by link, especially as traced in the fossils of North America. Evolution has taken a long time: how long the physicist and the astronomer must decide.

A scale insect threatened with ruin the orchards of California. Professor C. V. Riley decided that the pest was a native of Australia. Mr. A. Hoebele observes in Australia that the pest is kept down by ladybirds. These are accordingly sent to California where they destroy the scale insect and restore prosperity among the fruit-growers. Another pest, of olive trees, is devoured by an imported ladybird of another species. This plan extended to Portugal and Egypt with success. Grasshoppers killed by a fungus cultivated for the purpose. Introduction into the United States of the insect which fertilizes the Smyrna fig.

Dress is important, whether natural or artificial. Because they catch dust on their clothes, bees, moths and butterflies have brought about myriad espousals of flower with flower. Colours and scents of blossoms attract insects. A flower which in form, scent or hue varies gainfully is likely to survive while others perish. All the parts of a flower are leaves in disguise. Floral modes of repulsion and defence. Plants which devour insects, a habit gradually acquired. The mesquit tree tells of water. Plants believed to indicate mineral veins. Seeds as emigrants equipped with wings or hooks. Parasitic plants and their degradation. Tenants that pay a liberal rent. The gardener as a creator of new flowers. The modern sugar beet due to Mons. Vilmorin.