Charles Darwin
Darwin, aged 45 in 1854,
Charles Robert Darwin, (12 February 1809 – 19 April 1882) was an English naturalist. In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".
The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are inherited, then differential reproductive success will lead to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species
Although Darwin was very successful at convincing his contemporaries about the fact that evolution had occurred, he was much less successful at convincing his colleagues that his mechanism of Natural Selection was the major mechanism of evolutionary change. This was mainly because there was no satisfactory explanation for inheritance, or for how variation originated.
Darwin himself was plagued by his inability to understand inheritance, and was dissatisfied by his own theory of inheritance, pangenesis and blending inheritance, because blending suggested that variation should be halved each generation and would rapidly be lost.
Darwin's lack of a model of the mechanism of inheritance left him unable to interpret his own data that showed Mendelian ratios, even though he shared with Mendel a more mathematical and probabilistic outlook than most biologists of his time.
"The laws governing inheritence are quite unknown; no one can say why a peculiarity in different individuals of the same species…is sometimes inherited and sometimes not; why the child often reverts in certain characters to its grandfather or grandmother or other more remote ancestor." Charles Darwin, The Origin of Species, 1859
Darwin's own “pangenesis” model provided a mechanism for generating ample variability on which selection could act. It involved, however, the inheritance of characters acquired during an organism's life, which Darwin himself knew could not explain some evolutionary situations. [Once the particulate basis of genetics was understood, it was seen to allow variation to be passed intact to new generations, and evolution could then be understood as a process of changes in the frequencies of stable variants.]
Evolutionary genetics subsequently developed as a central part of biology. Darwinian principles now play a greater role in biology than ever before, which we illustrate with some examples of studies of natural selection that use DNA sequence data and with some recent advances in answering questions first asked by Darwin.
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