The Pamphlet Collection of Sir Robert Stout: Volume 31
Sketch of the Evidence
Sketch of the Evidence.
It is not my purpose, then, to attempt to prove Evolution. Yet it is necessary for the end I have in view that I should indicate some of the leading features in the body of evidence upon which the doctrine rest; so far, at least, as it relates to the origin of animal forms.*page 4
(1.) There is first what may be called the invariable tendency to vary, which is constant in all organisms. No two individuals of a family are absolutely alike.
(2.) Next, variations may be accumulated by the selection of the parents. It is upon this principle that the art of the stock breeder is based, and its results may be exemplified by the widely diversified forms, within the same species, of the race-horse and the London dray-horse.
(3.) All living things have a capacity for increasing in a geometrical ratio. If a pair produce ten young once during their lives, and these again are reproductive at a year old, twenty millions will be produced in ten years. Many animals, and most plants, increase faster than this. Even the elephant, which has the slowest rate of increase, would in five hundred years multiply from a single pair to fifteen millions.
(4.) But notwithstanding this enormous rate of increase, the number of animals and plants in any country once stocked never permanently increases. It may fluctuate slightly from year to year, but the average remains the same. It follows that the deaths must equal the oinks. If the number of sparrows, say in England, is on the average half a million, and if a million of young ones are hatched every year, then before the next year a million sparrows must die. When a million sparrows die annually, what determines which individuals die and which survive? We know that wild animals die of diseases, of hunger, of cold, by the attacks of enemies, &c. Will it Le the healthy or the sick that die of diseases, the strong or the weak that die of hunger, the well feathered or the poorly feathered that die of told, the active and wary or the slow and careless that will be killed by enemies?
(5.) In the answer to these questions is involved the law of the survival of the fittest, or natural selection. Any minute variation giving an animal an advantage in the struggle for life would tend to be inherited. The law of "survival of the fittest," by simply determining which out of the immense surplus born annually shall be the parents of the next generation, must lead to the modification of every part of an animal's organisation that affects its welfare sooner or later, of its whole organisation.
By the operation through enormous lengths of time of these principles stamped by the Author of Nature upon all organisms, have been evolved, from one parent form, or even from the "primordial slime," all living types of animals and plants. Such is the startling doctrine of Evolution.
* The summary which follows is compressed from an article in the Quarterly Review' for April, 1869.