The gradual change in organisms from the fossil record played a role. No naturalist had observed the sudden appearance of a new species in their lifetime. We have seen slow to rapid rates of evolutionary change within the lineage. Natural selection has four components that play a role in Darwin’s idea of variation. The first one was variation in which organism showed individual variation in appearance and their behavior. This involved an organism’s body size, hair color, facial markings and number of offspring. Although some organisms showed little to no variation, this was still important. The second was inheritance, which means that some traits will be passed down to their offspring. So, that means that those traits that were passed down, …show more content…
Mendel’s mode of inheritance was used to argue against natural selection. The variants and mutants observed by early geneticists had discrete effects. The species differed discretely and it was discovered that species could have arisen by discrete, systematic changes. Darwin’s theory reconciled with the facts of genetics that required characteristics that are not inherited. He concluded that continuous variation had the same Mendelian basis as discrete variation. He thought that populations have genetic variations that will continue to arise by mutations and recombination. These populations would evolve because of changes in gene frequencies. They would evolve because of the genetic drift, natural selection and gene flow. The most adaptive variants will have slight phenotypic effects, so that these changes are gradual. Diversification arises because of speciation, which is the gradual evolution of reproductive isolation. This process continues for a long time, which will produce enough changes to delineate higher taxonomic levels. They couldn’t reconcile Darwinism with the fossil record or heredity at this time, so therefore some people had a hard time believing