Hugo de Vries believed mutation causes speciation and hence called a single step large step as

De Vries proposed a theory of evolution that included the idea of "saltation," which refers to the sudden and large-scale changes in a species. According to de Vries, these abrupt changes were the result of mutations. Mutation, in the context of genetics, refers to any heritable change in the DNA sequence of an organism.

De Vries believed that mutations could lead to the sudden appearance of new species, bypassing the gradual accumulation of small variations proposed by Charles Darwin's theory of natural selection. In other words, he suggested that speciation (the process by which new species arise) could occur through a single, significant mutation event rather than through the gradual accumulation of small changes over time.