Question

According to Hugo de Vries, the mechanism of evolution is ____________.
A. Phenotypic variations
B. Multiple step mutations
C. Minor mutations
D. Saltations

Answer 1

Hint: Hugo de Vries is a Dutch botanist, by one of his independent rediscoveries of the Mendelism, he put forward his views regarding the formation of the new species in 1901. He also met some of the objections found in Darwin's theory.

Complete answer:
According to Hugo de Vries, new species are not formed by the continuous variations but by the sudden appearance of variations, which he named as mutations. He stated that the mutations are heritable and they persist in successive generations.
He conducted experiments on the Oenothera Lamarckiana, and found many aberrant types. When Oenothera Lamarckian was self-pollinated and its seeds were allowed to grow, the majority of the plants were similar to the parents, but a few of them were different plants. The different plants were also then self-pollinated and when their seeds were sown, majority of the plants were similar to the parents while a few were more different plants and this process continued generation after generation. These plants appeared to be a new species. Hugo de Vries suggested from his experiments that new types of the inherited characteristics may appear suddenly even without any previous indication of their presence in the race.
Hugo de Vries believed that mutations cause evolution and not the minor heritable variations as mentioned by Darwin. Mutations are directionless and random while Darwin’s variations are directional and small. Evolution is gradual according to Darwin, but Hugo de Vries believed that mutations caused species formation and hence known as saltation or single step large mutation.

Hence, the correct answer is option (D).

Note: Hugo de Vries’ Mutation Theory gives direct attention to mutations. But later on, it was thought that evolution cannot occur only by mutations. Natural selection and isolation of the mutants were also essential for evolution.