By Alfred Russel Wallace, Charles Darwin
Wallace spotted on expeditions to the Amazon and the Malay archipelego that mammals in Southeast Asia are extra complex than their Australian cousins. His advice used to be that the 2 continents had cut up prior to the higher tailored mammals had developed in Asia. The remoted Australian marsupials have been capable of thrive, while these in Asia have been pushed to extinction by means of festival from extra complicated mammals. This ended in his thought of ordinary choice, which he offered to the Linnean Society in 1858 with Charles Darwin. This quantity reprints these papers offered to the Linnean Society.
Read or Download Part I: Contributions to the Theory of Natural Selection Part II: On the Tendency of Species to Form Varieties; The Evolution Debate, 1813-1870 (Volume IX) PDF
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Additional resources for Part I: Contributions to the Theory of Natural Selection Part II: On the Tendency of Species to Form Varieties; The Evolution Debate, 1813-1870 (Volume IX)
Sample text
The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be the weakest—the very young, the aged, and the diseased—while those that prolong their existence can only be the most perfect in health and vigour—those who are best able to obtain food reg ularly, and avoid their numerous enemies. It is, as we commenced by remarking, “a struggle for existence,” in which the weakest and least perfectly organized must always succumb.
On the average all above one become food for hawks and kites, wild cats or weasels, or perish of cold and hunger as winter comes on. This is strikingly proved by the case of particular species; for we find that their abundance in individuals bears no relation whatever to their fertility in producing offspring. Perhaps the most remarkable instance of an immense bird population is that of the passenger pigeon of the United States, which lays only one, or at most two eggs, and is said to rear generally but one young one.
Among birds, the ptarmigan is a fine example of protective colouring. Its summer plumage so exactly harmonizes with the lichen-coloured stones among which it delights to sit, that a person may walk through a flock of them without seeing a single bird; while in winter its white plumage is an almost equal protection. The snow-bunting, the jerfalcon, and the snowy owl are also white-coloured birds inhabiting the arctic regions, Mimicry, and other protective resemblances among animals 23 and there can be little doubt but that their colouring is to some extent protective.