[Biology Class Notes] on Anagenesis Pdf

Transformation of a particular lineage of organisms to a different state which can be justified as a new species from its ancestral species is known as anagenesis. It is the constant evolution of a species that continues to exist as an interbreeding population. Without the branching, if the evolutionary line is descent, then the formation of new species is known as phyletic transformation or gradualism. It is a mechanism in which one species shelves onto another due to evolutionary changes within a lineage. The newly formed species completely overshadow the ancestral species causing the ancestral species to be extinct.

Anagenesis and Cladogenesis

Cladogenesis is different from anagenesis, as Cladogenesis refers to the phenomenon of evolutionary splitting of a parent species into two distinct species forming a clade. This may occur naturally when few organisms end up in often distant new areas or when environmental changes cause several extinctions. To find out whether a species is formed through Cladogenesis or Anagenesis several scientists and researchers examine fossil, molecular evidence from the DNA of different living species, etc.

Characteristics of Anagenesis

• To improve the functions the complexity and rationalization of organs is increased

• The central nervous system complexity is increased

• It increases the resistance to the changes in the environment 

• It divides the labor into the body parts 

• It degenerates the unnecessary organs into parasites by increasing the parasitic nature

• By this process, arthropods and crustaceans show a high tendency towards speciation.

Cause of Anagenesis

As the speciation occurs, several lineages bifurcate and discontinue interbreeding. This may lead to the development of original species without any progression and evolution. In an anagenesis revolution, during the speciation, the original population increases quickly and acquires genetic variation. This is eventually through recombination of genetic material or mutation which provides a stable environment. The genetic drift and selection process can also lead to the creation of new species.

Anagenetic Evolution

The evolution process can take place by anagenesis. In anagenetic evolution, changes occur within a lineage or by cladogenesis in which lineage splits into two or more separate lines. In this new species are formed after many long years.

Anagenesis Example

This is a slow process that takes thousands or millions of years.

The peppered moth is the best example of anagenesis as it happens in a single species. The collection of moths were made in England in the year 1850 before industrialization. It was observed that there were more white-winged moths than black-winged moths. But after industrialization nearly around 1920 it was noticed that there were more dark-winged moths than the white-winged moths.

After observations, it was concluded that predators spot a month against a contrasting background. Due to industrialization trees, trunks become black due to smoke and soot. So, white-winged moths didn’t survive due to predators and dark-winged moths survived. But if we see before industrialization set in, white-colored lichens covered the trees and in that background, the white-winged moths survived and dark-winged moths we’re picked out by predators. This shows that in a mixed population the one who can better adapt can survive and increase in population size.

Difference Between Anagenesis and Cladogenesis 

Anagenesis

• It is an evolutionary change of a single lineage in which a single taxon is replaced by another without branching.

• In this branching of lineage doesn’t occur.

• It is an evolution within a lineage.

• It is called phyletic evolution or progressive evolution.

• It does not promote biological diversity

• It has three modes Tachytely, Horotely, and Bradytely.

Cladogenesis

• It is an evolutionary change of a particular species in which new species are branded off from a common ancestral species.

• In this branching of the lineage occurs.

• It is an evolution which results in the splitting of the lineage.

• It is also called a branching evolution.

• In this, a single gene pool is split into several gene pools.

• It promotes biological diversity since it increases the number of species.

• It has three modes Tachyschizia, Horoschizia and Bradyschizia.