Single step large mutation leading to speciation is also called saltation.

Saltation refers to a large and sudden genetic change or mutation that occurs in a single step, leading to the formation of a new species. This phenomenon is considered to be a rare event in evolutionary biology and is in contrast to the gradual accumulation of small genetic changes over time, which is the basis of Darwin's theory of natural selection.

Explanation:
To understand saltation, it is important to first grasp the concept of speciation. Speciation is the process by which new species arise from existing ones. It occurs when populations of a species become reproductively isolated from each other and can no longer interbreed. This reproductive isolation can be due to various factors such as geographic barriers, genetic differences, or changes in behavior.

Saltation suggests that speciation can occur through a single large genetic change or mutation, rather than through the accumulation of many small changes over time. This concept challenges the traditional view that speciation is a gradual process driven by natural selection.

Saltational speciation is often considered to be a rare event because large mutations are less likely to occur compared to smaller mutations. Additionally, even if a large mutation does occur, it must confer a significant advantage to the organism in order to spread through the population and lead to speciation.

Contrast with gradualism:
The concept of saltation contrasts with gradualism, which proposes that speciation occurs through the slow accumulation of small genetic changes over long periods of time. Gradualism aligns with Darwin's theory of natural selection, where small variations within a population are acted upon by selective pressures, leading to the evolution of new species over time.

Conclusion:
While saltation suggests that speciation can occur through a single step large mutation, this concept is considered to be a rare occurrence in evolutionary biology. The gradual accumulation of small genetic changes over time, in line with natural selection, remains the predominant mechanism for speciation.