Darwin, whose theory of evolution has had a profound influence on psychology, was born in ShrewsburyEngland, the son of a doctor and grandson of the celebrated Erasmus Darwin, a poet, physician, and philosopher. He entered Cambridge in 1827, and after three years of study for the ministry became disinterested in this field and began to devote himself to the study of botany and zoology. Soon after graduating, in 1831, he took a position as naturalist aboard a ship, the Beagle, and made a five-year scientific cruise around the world. In the course of the trip, he made innumerable observations and collected a large number of plant and animal specimens. Two years after his return Darwin became secretary of the Geological Society in London, and a year later published The Journal of a Naturalist. This was followed by Zoology of the Voyage of the Beagle (1840) and The Structure and Distribution of Coral Reefs (1842). Darwin was not a healthy man, and retired to the country in an effort to regain his health. There he devoted himself to the intensive study of several living species, with one major question in mind: “Why were animals so well adapted to their environment and what force eliminated those that were not as fit to survive?” In attempting to answer this double-barreled question, he was influenced by evolutionary ideas which had been recurrent in Western thought ever since the Greeks, but which had gathered force during the preceding fifty years. Goethe had made use of this concept in his studies of botany in 1790, and in his suggestion that the vertebrate skull is nothing more than a modified and developed spinal column. His own grandfather, Erasmus Darwin, had sought to account for the multiplicity of species by suggesting a theory of transmutation. Laplace had applied an evolutionary explanation to the development of the planetary system from a single nebula. Lyell, whom Darwin knew, had described the orderly geological changes through which the earth itself evolved, and had also studied extinct fossil organisms found at different strata, indicating that they therefore stemmed from different eras. Lamarck had suggested that animal forms are modified by their attempts to deal with the environment, and had developed the theory that these acquired changes were passed on to the offspring. All these ideas, then, were “in the air” at the time of Darwin—but it was a specialist in quite a different field who helped to provide the key to his problem: the great economist Malthus. In his Essay on the Principle of Population he had pointed out that improvement in food production increases food output arithmetically, while population increases geometrically. This process, he held, inevitably leads to overpopulation, which is eliminated in part by starvation, war, and disease. When Darwin read this book, he felt that the concept of struggle for existence was basic to the entire process. From this idea he developed the biological theory that since an excess of offspring is produced among animals, only the fittest survive—that is, only those adapted to their particular environment in terms of getting food and resisting their enemies. He also theorized that the fitness itself was based on a process of natural selection. Due to variations in the hereditary process, some animals developed characteristics that helped them adapt to the environment, while others fell by the wayside. The ones that survived passed their characteristics on to new generations and eventually produced a new species.Darwin collected a huge amount of evidence in support of his views, and in 1859 published his monumental work, The Origin of Species: By Natural Selection; or the Preservation of Favored Races in the Struggle for Life. All 1250 copies of the first edition were sold out on the day of publication, and the impact on the scientific community, as well as the religious community, was immediate and immense.One of the sciences most affected by Darwin’s theory was psychology. At least five general trends can be traced to its influence. First, functionalism, which looked upon mental processes as adaptive measures, became the dominant approach, and structuralism, with its emphasis on analysis of the contents of consciousness, receded into the background. Second, comparative psychology, with its study of animal behavior, came to the fore, not only because of Darwin’s recognition of the biological continuities between men and animals, but also because he noted similarities between the reasoning processes of men and those of the higher vertebrates. Third, studies of expressive behavior were stimulated by Darwin’s book Expression of Emotion in Man and Animals (1872), in which he showed, for example, that the hair tends to stand on end during displays of anger, probably to make the body seem larger and thereby frighten off enemies. Fourth, genetic psychology received a strong impetus from the evolutionary doctrine, and as a result many studies of the development of the individual from infancy to old age were made. Fifth, the concept of survival of the fittest focused attention on individual differences and stimulated the study of hereditary tendencies, genius, and the measurement of human capacities through psychological tests. See EXPRESSIVE BEHAVIOR, FUNCTIONALISM, DIFFERENTIAL PSYCHOLOGY, GENIUS, INTELLIGENCE TESTS.