Darwin and Wallace both realized that if an animal has some trait that helps it to withstand the elements or to breed more successfully, it may leave more offspring behind than others. In this struggle for existence, survival and reproduction do not come down to pure chance.
Ferreira © California Academy of Sciences. Carrier pigeon image courtesy of The Pigeon Cote Brunner pouter image courtesy of Layne’s Pigeon Site Rock dove image courtesy of Dr.
Selection of traits The carrier pigeon (bottom left) and the Brunner pouter (bottom right) were derived from the wild rock pigeon (top). Individuals must compete, albeit unconsciously, for what little food there is. And their food supply, like that of a nation, is not infinite. They are vulnerable to droughts and cold winters and other environmental assaults.
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But the world is not overrun with them, or any other species, because they cannot reproduce to their full potential. It should take very little time for the world to be knee-deep in beetles or earthworms. When Darwin and Wallace read Malthus, it occurred to both of them that animals and plants should also be experiencing the same population pressure. A nation could easily double its population in a few decades, leading to famine and misery for all. An English parson named Thomas Malthus published a book in 1797 called Essay on the Principle of Population in which he warned his fellow Englishmen that most policies designed to help the poor were doomed because of the relentless pressure of population growth. Interestingly, Darwin and Wallace found their inspiration in economics. But in the mid-1800s, Darwin and the British biologist Alfred Russel Wallace independently conceived of a natural, even observable, way for life to change: a process Darwin called natural selection. Many German biologists conceived of life evolving according to predetermined rules, in the same way an embryo develops in the womb. Lamarck, for example, thought that life strove over time to rise from simple single-celled forms to complex ones. Typically, they claimed that evolution was guided by some long-term trend. Lamarck and others had promoted evolutionary theories, but in order to explain just how life changed, they depended on speculation. It was Darwin’s genius both to show how all this evidence favored the evolution of species from a common ancestor and to offer a plausible mechanism by which life might evolve. The finches also differed in beak shape, food source, and how food was captured. He found several species of finch adapted to different environmental niches. Pre-Darwinian ideas about evolution A visit to the Galapagos Islands in 1835 helped Darwin formulate his ideas on natural selection. At the same time, embryologists and other naturalists studying living animals in the early 1800s had discovered, sometimes unwittingly, much of the best evidence for Darwin’s theory.
Geologists and paleontologists had made a compelling case that life had been on Earth for a long time, that it had changed over that time, and that many species had become extinct. But as earlier chapters in this history have shown, the raw material for Darwin’s theory had been known for decades. The genius of Darwin (left), the way in which he suddenly turned all of biology upside down in 1859 with the publication of the Origin of Species, can sometimes give the misleading impression that the theory of evolution sprang from his forehead fully formed without any precedent in scientific history. Information on controversies in the public arena relating to evolution.Alignment with the Next Generation Science Standards.The big issues – Pacing, diversity, complexity, and trends.Macroevolution – Evolution above the species level.Microevolution – Evolution within a population.Mechanisms: the processes of evolution – Selection, mutation, migration, and more.The history of life: looking at the patterns – Change over time and shared ancestors.An introduction to evolution: what is evolution and how does it work?.
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