When Darwin wrote On the Origin of Species, no transitional fossils had been discovered, but Darwin predicted that some would be found. On which of the following concepts was Darwin basing his bold prediction? More than one answer is expected.

Choose all that are correct
a. All major groups of organisms living today descended from preexisting groups. There must therefore be fossils with features that link different major groups, both living and extinct, to one another.
b. Major transitions in the history of life occur over long periods of time and in small steps rather than major leaps, with groups of animals evolving traits that did not exist in the ancestral groups.
c. Darwin reasoned that eventually the fossils of all organisms that ever existed would be discovered and that there would have to be some transitional forms among them.
d. Individual organisms can change from one form to another, like a fish becoming a land animal, and give rise to new species. The transitional forms must therefore exist in the fossil record.

Darwin is considerd as the father of evolution. He explains the role of natural selection on the theory of evolution. He wrote a book On the Origin of Species. Darwin believes that there are some transitional fossils in the evolution of an organism.

Darwin believes on the transitional state of fossil because all the organisms have been descended from the earlier groups. Some fossil evidence shows the connection between the living and extinct group. The evolution has occurred in slow steps and the organism has evolved the trait that are not present in the ancestor organism.

Thus, the correct answer is option (a) and (b).