Anagenetic

Anagenetic refers to a type of evolutionary change that involves the gradual transformation of a single lineage over time. This contrasts with cladogenesis, which involves the splitting of one lineage into two or more. In anagenesis, a species evolves into a new species without branching. This means that the ancestral species is completely replaced by its descendant species. The fossil record is often used to study anagenetic change, as it can show a series of transitional forms that document the gradual evolution of one form into another. For example, the evolution of the horse from its small, multi-toed ancestors to the modern, single-toed horse is often cited as an example of anagenesis.

Anagenetic evolution typically involves a series of small, incremental changes that accumulate over many generations. These changes can be driven by various factors, including natural selection, genetic drift, and mutation. Over long periods, these accumulated changes can lead to significant differences between the ancestral and descendant populations, to the point where they are considered distinct species. While speciation through cladogenesis is more common, anagenetic speciation is a valid mode of evolutionary change and plays a role in the diversification of life. It is important to note that distinguishing between anagenesis and cladogenesis in the fossil record can be challenging due to the incompleteness of the fossil record itself.