Difference Between Atavism and Retrogressive Evolution

The key difference between atavism and retrogressive evolution is that atavism is the sudden reappearance of ancestral characters in an individual while retrogressive evolution is the moving of species in the entire population towards primitive characters.

Traits can appear or disappear over time. Throughout the evolutionary process, ancestral traits have changed or disappeared over generations. Moreover, organisms develop from simpler forms to complex forms. Natural selection is a key mechanism of evolution. Atavism and retrogressive evolution are two concepts that explain the simplification of a structure. Atavism is the reappearance of an ancestral trait that had been lost during evolution. In retrogressive evolution, organisms develop into simpler forms from complex forms. In both instances, organisms move towards primitive characteristics.

1. Overview and Key Difference
2. What is Atavism
3. What is Retrogressive Evolution
4. Similarities Between Atavism and Retrogressive Evolution
5. Side by Side Comparison – Atavism vs Retrogressive Evolution in Tabular Form
6. Summary

What is Atavism?

Atavism is the sudden reappearance of ancestral characteristics in an individual. Generally, organisms undergo evolution over time, and they lose ancestral traits. Some ancestral traits which were lost during the process of evolution over generations can suddenly reappear in organisms. Atavism refers to such recurrence of ancestral traits in a subsequent generation. Atavism has been observed in humans as well. Infants born with vestigial tails, humans possessing large teeth, and colour blindness are examples of atavism in human. Chickens with teeth and dolphins with legs are two more examples for atavism.

Difference Between Atavism and Retrogressive Evolution

Figure 01: Atavism

There are several causes for atavism. Due to a mutation, the dormant or suppressed genes can be expressed, giving ancestral traits. Moreover, errors in gene regulation can also reverse ancestral traits.

What is Retrogressive Evolution?

Retrogressive evolution is the return of species of an entire population to one or other of their earlier forms. This is kind of simplification of structure. Most of the time, in retrogressive evolution, the reappearance of ancestral characters takes place. However, unlike in atavism, the reappearance takes place in the entire population, without being restricted to an individual. Therefore, in retrogressive evolution, organisms develop into simpler forms.

Retrogressive evolution is the opposite of progressive evolution. In progressive evolution, simple forms of organisms develop into complex forms. They attain a highly complex structure. However, due to progressive evolution, they become more independent. Retrogressive evolution is common in parasitic organisms. Parasitic organisms develop their own feeding systems rather than deriving energy from their hosts.

What are the Similarities Between Atavism and Retrogressive Evolution?

Both atavism and retrogressive evolution are two phenomena that simplify the structure of an organism.
In both atavism and retrogressive evolution, organisms move towards simple form or ancestral form.
In both instances, organisms lose evolved features.

What is the Difference Between Atavism and Retrogressive Evolution?

Atavism is the sudden appearance of ancestral traits in an individual. Retrogressive evolution is the process of loosing evolved features due to the movement of organisms from complex forms to simple forms. So, this is the key difference between atavism and retrogressive evolution.

Below is a summary tabulation of the difference between atavism and retrogressive evolution.

Summary – Atavism vs Retrogressive Evolution

Atavism is the reappearance of an ancestral trait that had been lost during evolution. Therefore, ancestral traits can suddenly appear in subsequent generations, mainly due to mutations or errors in gene regulation. Retrogressive evolution is the conversion of organisms from complex forms to simple forms. Organisms lose evolved characteristics. In other words, it is the movement of organisms towards primitive characters. Retrogressive evolution is the opposite of progressive evolution. Thus, this is the summary of atavism and retrogressive evolution.

Reference:

1. “Atavism: Embryology, Development And Evolution | Learn Science At Scitable”. Nature.Com, 2020, Available here.

Image Courtesy:

1. “Tubal Pregnancy with embryo” By Ed Uthman, MD (Flickr, Wikipedia) – (2014). WikiJournal of Medicine 1 (2): 7. DOI:10.15347/wjm/2014.007. (Public Domain) via Commons Wikimedia