Introduction to Anagenesis
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.
FAQs on Anagenesis
1. What is anagenesis in evolution?
Anagenesis, also known as phyletic evolution, is a pattern of evolution where a single species evolves into a new species over time without splitting. In this process, the entire population undergoes gradual changes, and the ancestral form is eventually replaced by the new, descendant form. It represents a transformation within a single lineage rather than the branching off of new lineages.
2. How does anagenesis differ from cladogenesis?
Anagenesis and cladogenesis are two fundamentally different patterns of speciation. The primary difference lies in how new species are formed.
- Lineage: In anagenesis, evolution occurs along a single, unbranching lineage. In cladogenesis, an ancestral species splits into two or more distinct descendant species, creating a branching pattern.
- Species Count: Anagenesis does not increase the total number of species; it transforms one species into another. Cladogenesis increases biological diversity by adding new species.
- Ancestral Species: The ancestral species becomes extinct through transformation in anagenesis. In cladogenesis, the ancestral species may continue to exist alongside the new species or become extinct.
3. Can you provide a real-world example of anagenesis?
A classic example often cited for anagenesis is the evolution of the peppered moth (Biston betularia) in England. Before the Industrial Revolution, the light-coloured moths were more common as they blended in with lichen-covered trees. However, as industrial pollution blackened the tree trunks, the dark-coloured variant became advantageous for camouflage against predators. Over time, the population's characteristics shifted, and the dark-winged moth became the dominant form in that single lineage due to directional selection.
4. Does anagenesis increase the total number of species?
No, anagenesis does not increase the total number of species. It is a process of linear transformation where an entire ancestral population evolves into a new form that is different enough to be classified as a new species. Since the original lineage does not split, the number of species remains the same—one species is simply replaced by another. This is a key distinction from cladogenesis, which is the primary mechanism for increasing biodiversity by splitting one lineage into multiple.
5. What evolutionary mechanisms drive anagenesis?
Anagenesis is driven by the cumulative effect of several core evolutionary mechanisms acting on a population over a long period. The primary drivers include:
- Natural Selection: When environmental conditions change, certain traits become more advantageous, leading to a gradual shift in the population's genetic makeup.
- Mutation: The ultimate source of new genetic variation, providing the raw material for evolutionary change.
- Genetic Drift: Random fluctuations in allele frequencies, which can have a significant impact, especially in smaller populations, causing certain traits to become fixed or lost over time.
6. How does the concept of anagenesis relate to phyletic gradualism?
Anagenesis and phyletic gradualism are closely related concepts that describe the same evolutionary process from different perspectives. Anagenesis refers to the pattern of evolution—a single, unbranching lineage transforming over time. Phyletic gradualism, on the other hand, describes the tempo of this change, suggesting that evolution occurs at a slow, constant, and gradual rate. Therefore, anagenesis is often considered to occur via the model of phyletic gradualism.
7. What happens to the ancestral species in anagenesis?
In anagenesis, the ancestral species effectively becomes extinct through transformation. It does not die out in the conventional sense or coexist with the new species. Instead, the entire gene pool of the ancestral population gradually changes over generations to such an extent that it becomes the new descendant species. The original form is completely replaced, a process sometimes called pseudoextinction.
