Darwin

Many people assume that Darwin was the first person to come up with the idea of evolution, but he was not. In the early nineteenth century it was already known that the earth is very old and that different kinds of plants and animals have lived at different times. Many people speculated that the appearance and disappearance of all those species might be explained by evolution (or descent with modification as it was then called). But evolution was rejected by scientific thinkers because no one could imagine how one species could change into another. What could the mechanism possibly be? Instead, they accepted the theory of ‘catastrophism,’ according to which a series of great disasters had occurred which the existing species were destroyed and then replaced by God in a new act of creation. Today catastrophism may seem absurd, but in the early nineteenth century it was the best theory available, and many scientist accepted it. Then Darwin changed everything by proposing a viable theory of how evolution might take place. The Theory of Natural Selection, which he set out in his book ‘On the Origin of Species (1859), supplied the mechanism needed to explain how species might evolve over time. ~ Page 17

Darwin’s genius was in realzing that three well-known facts, taken together, could explain evolutionary change. First, there is the geometrical increase of populations. Organisms reproduce in such numbers that, if left unchecked, the members of any other species would soon overrun the earth. Second, there is the ‘heritability of traits.’ An organism’s descendants tend to resemble it -- each individual inherits the characteristics of its parents. Third, there is ‘variation.’ Although individuals resemble their parents, they are not exactly like their parents. There is random small differences between them. ~ Page 17