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Evolution
The World of Darwin
Darwin's Observations
Darwin's Observations
A search for the "mechanism" of evolution did not begin with Darwin, but his evidence for the Origin of Species by Means of Natural Selection, published in 1859, was so comprehensive it swept away all other theories and became a major turning point in the study of biology.

Among the vast body of data supplied by Darwin are five key observations:

  1. More offspring are born than ever survive to become adults (an idea he found in a 1789 essay on economics by Reverend Thomas Malthus). Female fish can lay thousands of eggs, but usually only one or two survive to become adults.

  2. Among these offspring, there is a range of values for any trait; in other words there is variation. Some goldfish have golden scales, some have orange scales, some have brownish scales, and some have a mixture.

  3. This variation extends to all traits, even those vital for the survival of the individual. An eagle, which depends on superior eyesight to locate its prey, can still be born shortsighted. All variations are, therefore, random and not specifically directed toward any preferential adaptation.

  4. All offspring compete within their natural environments for food, resources, mates, and safety from harm. Those with the weakest combinations of traits die, whereas those with the best combinations of traits survive to reproductive maturity more often. There is a natural selection for those individuals that are the fittest.

  5. The survivors pass on their traits to the next generation and the process is repeated. Over millions of years, such gradual changes lead to changes in the whole population and hence to the origin of an entirely new species.

Put in modern terms, Darwin explained that random events create changes in the genotype of the organisms. These changes are then reflected in variations in the phenotype.

Combinations of these variations, distributed among large numbers of offspring and expressed as different phenotypes, are in competition for survival.

Nature and the natural environment "select" the most fit phenotype and discard the least fit phenotypes. Darwin, therefore, viewed evolution as the gradual accumulation of genotypic change in a population of organisms to the point that the population becomes a new species.


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© 2001, Professor John Blamire