Origin of Variation: The question arises regarding the origin of variation within populations and how speciation occurs. Although Gregor Mendel had discussed inheritable factors influencing phenotype (genes), Charles Darwin either did not consider or did not emphasize this aspect.

Hugo de Vries and Mutations: In the early 20th century, Hugo de Vries, based on his work with evening primroses, introduced the concept of mutations. He proposed that large differences in traits could arise suddenly within a population due to mutations. De Vries believed that mutations, not the minor heritable variations discussed by Darwin, were responsible for evolution.

Mutations and Evolution: Mutations are random and unpredictable changes in an organism’s genetic material (DNA). Unlike the small, directional variations of Darwin, mutations are often larger in scale and do not follow a specific direction. De Vries referred to this process as “saltation,” indicating that a single large mutation could lead to speciation.

Population Genetics: Subsequent studies in population genetics helped clarify the mechanisms of evolution. They showed that both small heritable variations and rare, larger-scale mutations (like those studied by de Vries) contribute to the overall process of evolution.

Key Points:

• Darwin’s concept of evolution involved gradual, small, and directional variations within populations.
• De Vries introduced the idea of mutations as large and abrupt changes causing speciation.
• Mutations are random and not necessarily directed toward adaptation.
• Modern understanding of evolution recognizes the role of both small, heritable variations and occasional, large-scale mutations in driving the diversity of life.