Not afraid to announce unorthodox views, Wallace published a radically innovative theory of evolution (minus only natural selection) in an 1855 paper. While Charles Darwin sat on his revolutionary theory for 20 years, terrified of his conservative contemporaries, Wallace boldly set out to solve the great problem of the origin of species. Those organisms are not necessarily the fittest of their species, but it is their genes that get passed on to the next generation.Since the 1970s, the story of Wallace has become something like this: In genetic drift, some organisms-purely by chance-produce more offspring than would be expected. For example, a phenomenon known as genetic drift can also cause species to evolve. Today, it is known to be just one of several mechanisms by which life evolves. Biologists have since observed numerous examples of natural selection influencing evolution. Natural selection was such a powerful idea in explaining the evolution of life that it became established as a scientific theory. This means that if an environment changes, the traits that enhance survival in that environment will also gradually change, or evolve. Natural selection is sometimes summed up as “survival of the fittest” because the “fittest” organisms-those most suited to their environment-are the ones that reproduce most successfully, and are most likely to pass on their traits to the next generation. Those that are lacking in such fitness, on the other hand, either do not reach an age when they can reproduce or produce fewer offspring than their counterparts. Those that are better physically equipped to survive, grow to maturity, and reproduce. In the theory of natural selection, organisms produce more offspring than are able to survive in their environment. ![]() Darwin and a scientific contemporary of his, Alfred Russel Wallace, proposed that evolution occurs because of a phenomenon called natural selection. But evolution did not reach the status of being a scientific theory until Darwin’s grandson, the more famous Charles Darwin, published his famous book On the Origin of Species. When it comes to the evolution of life, various philosophers and scientists, including an eighteenth-century English doctor named Erasmus Darwin, proposed different aspects of what later would become evolutionary theory. Scientists talk about evolution as a theory, for instance, just as they talk about Einstein’s explanation of gravity as a theory.Ī theory is an idea about how something in nature works that has gone through rigorous testing through observations and experiments designed to prove the idea right or wrong. In science, the word “theory” indicates a very high level of certainty. His idea, however, was not a theory in the scientific meaning of the word, because it could not be subjected to testing that might support it or prove it wrong. ![]() From this reasoning, he proposed that all life began in the sea.Īnaximander was correct humans can indeed trace our ancestry back to fish. He concluded that those ancestors must be fish, since fish hatch from eggs and immediately begin living with no help from their parents. Noting that human babies are born helpless, Anaximander speculated that humans must have descended from some other type of creature whose young could survive without any help. Ideas aimed at explaining how organisms change, or evolve, over time date back to Anaximander of Miletus, a Greek philosopher who lived in the 500s B.C.E.
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