Anagenesis - Characteristics, Defination, Causes

Edited By Irshad Anwar | Updated on Sep 30, 2024 12:37 PM IST

The evolutionary terms anagenesis and cladogenesis form the crux of evolutionary biology, especially in speciation. These terms refer to the process describing how species evolve over time, spreading disparate paths as part of their evolutionary routes. Anagenesis represents divergent pathways of evolution that shape biodiversity. This topic is from biology class 12 chapter Evolution and is relevant for students appearing for CBSE boards, NEET, AIIMS, and other entrance exams for medicine.

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What Is Anagenesis?
Key Characteristics Of Anagenesis
Anagenesis Vs. Cladogenesis
Anagenesis Speciation
Example Of Anagenesis
Cladogenesis Vs. Anagenesis In Speciation
Anagenesis And Cladogenesis In Biotechnology
Tips, Tricks, And Strategies To Prepare For Anagenesis
Weightage of Questions from Anagenesis in Different Exams
Types Of Questions Asked On Anagenesis In Different Exams

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What Is Anagenesis?

Anagenesis can also be termed "phyletic evolution" therefore, the gradual build-up of changes within a single lineage over time. This is speciation whereby one species evolves directly into another without the formation of new species. The new species supplants the old, yet no new species are produced. It stands in contrast to cladogenesis, in which one species divides into two or more species that are quite separate. Anagenesis simply states that in evolution, an ancestor species turns into a new species through the centuries due to chromosomal mutations, natural selection, and shifts in the environment.

Key Characteristics Of Anagenesis

Some distinctive features of anagenesis are given below:

Straight Line Evolution: While in the process of anagenesis, one species will turn into another with no division of species.
Species Replacement: Species will eventually replace the original ancestral species since there is no original species anymore.
No Increase in Diversity: The change does not make any increase in the number of species, but only one species changes into another.
Slow Change: This process is normally slow and takes millions of years.

Anagenesis Vs. Cladogenesis

Anagenesis and cladogenesis represent two different paths of evolutionary change.

Feature	Anagenesis	Cladogenesis
Evolution Type	Linear evolution (single lineage transformation)	Branching evolution (species split)
Biodiversity	Does not increase biodiversity	Increases biodiversity
Speciation	Involves gradual change within a lineage	Involves divergence and formation of new species
Example	Evolution of modern horses from Eohippus	Darwin’s finches evolved into different species
Species Replacement	Old species are replaced by new species	Old species may coexist with new species

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Anagenesis Speciation

The other type of speciation is anagenesis, but this process does not contribute to species diversity at all. Instead, it's more about how the process of one species gradually and constantly turns into another. Environmental pressures, mutations, and natural selection are the driving forces behind these changes. Eventually, the population is so transformed that it is regarded as a new species.

Example Of Anagenesis

A good example is the history of the modern horse, Equus, with its ancestor Eohippus. The species diversity over millions of years has evolved through size changes, limb structures, and dentition, without ever splitting into several species at any point in the evolutionary process.

Cladogenesis Vs. Anagenesis In Speciation

Both anagenesis and cladogenesis are significant parts of speciation but describe different results of an evolutionary process.

Anagenesis: one species changes into a new species. There is no increase in the number of species.

Cladogenesis: a parent species divides into two or more daughter species. There is an increase in biodiversity.

Anagenesis And Cladogenesis In Biotechnology

The study of biotechnologies associated with evolutionary studies may depend on the difference between anagenesis and cladogenesis. These concepts tracing lineage and evolutionary relationships are used by the evolutionary biotechnologies involved in gene editing, species evolution, or genetic modification. Therefore, CRISPR and other biotechnology tools can trace back the evolutionary changes by comparing the ancestor's genes with modern species' genes.

Tips, Tricks, And Strategies To Prepare For Anagenesis

Given below are some tricks, tips and strategies to prepare for the topic of anagenesis:

Study Aids

Diagrams and Flowcharts: Draw diagrams illustrating the differences between anagenesis and cladogenesis.

Tables: Create tables showing comparisons between anagenesis and cladogenesis. This will further allow you to understand the difference between them.

Mnemonics

Remember that Anagenesis means linear evolution and Cladogenesis means branching by using the mnemonic "A-Always Linear, C-Constant Branching".

Real-Life Example

An example of anagenesis is seen in the modern horse's evolution, as the modern horse species evolved in a linear fashion, whereas the example of cladogenesis is seen in Darwin's finches which branched out into multiple different species.

Flashcards

Use flashcards to remember key differences and examples of anagenesis and cladogenesis.

Weightage of Questions from Anagenesis in Different Exams

Below is the weightage of questions asked from anagenesis topic in different exams over the years:

Exam Type	Weightage of Anagenesis
CBSE Board Exams	2-3%
NEET	2-3%
Nursing Entrance Exams	1-2%
Paramedical Entrance Exams	1-2%

Types Of Questions Asked On Anagenesis In Different Exams

The table below indicates the types of questions asked on biology in different exams:

Exam Type	Types of Questions
CBSE Board Exams	Short answers on definitions and differences between anagenesis and cladogenesis. Examples of evolutionary changes in species.
NEET	MCQs on evolutionary processes like speciation, differences between anagenesis and cladogenesis, and examples of speciation.
Nursing Entrance Exams	Assertion and reason questions on evolutionary theories, including examples of anagenesis and cladogenesis in real-life biology.
Paramedical Entrance Exams	Questions on how anagenesis impacts genetic diversity, short answers on examples of anagenesis in evolutionary biology.

Also Read:

Theories of Evolution	Evidence of Evolution
Difference Between Homologous and Analogous Structures	Lamarckism and theory
Modern Synthetic Theory of Evolution	Difference between Spontaneous and Induced Mutation

Frequently Asked Questions (FAQs)

1. What is meant by "phyletic evolution"?

Phyletic evolution, also known as phyletic gradualism, is defined as the evolutionary changes that take place within a single population or lineage. According to this theory that is given by Darwin, evolution takes place at a constant rate, and the formation of new species is the result of gradual changes that usually occur in the ancestral population. Phyletic evolution makes use of sufficient changes within a lineage such that it becomes easy to distinguish and is considered a separate species from its ancestor.

2. How can we define genetic drift?

Genetic drift is defined as the random changes that take place in allele frequencies from one generation to another and that usually take place within a population. Genetic drift is an event that is considered to focus on sampling error or chance.

3. Can we say speciation is a result of anagenesis?

Speciation is defined as the evolutionary process due to which there is the formation of distinct species that do not interbreed with each other. It is usually caused by cladogenesis and not anagenesis.

4. Differentiate between anagenesis and cladogenesis.

In cladogenesis, new species arise through the splitting of ancestral species into two or more species. In anagenesis, new species arise because of the transformation of many ancestral species. This process does not include species splitting into two new specie

5. Which increases biodiversity, anagenesis or cladogenesis?

Cladogenesis increases biodiversity because it leads to the formation of new species, while anagenesis does not as it only transforms a single species.

6. What is anagenesis and cladogenesis?

In anagenesis, the original species is replaced by the new one, and the evolution is linear without any branches. On the other hand, the process of branching evolution of one species that splits into two or more distinct species is called cladogenesis.

7. What Cladogenesis vs. anagenesis speciation?

In cladogenesis, the parent species splits up into several species that increase diversity and contribute to speciation. Anagenesis is where one species transforms into another but does not increase in numbers.

8. Example of anagenesis?

A common example of anagenesis is the evolution of the horse, where the ancient horse species Eohippus gradually transformed into modern horses (Equus) over millions of years.