What is parallel evolution and parallelism
In evolutionary biology, it is common to observe a situation where genetically related groups of organisms separate (divergence occurs) and subsequently encounter similar environmental conditions. As a result, they independently develop a similar external appearance. This process is called parallel evolution.
A specific case of this process is parallelism. Its main feature is convergent development (convergence of traits), which occurs strictly on the basis of homologous organs (structures having a common evolutionary origin).
A classic example of parallelism is the evolution of felines: the trait of "saber-toothedness" (excessively developed canines) repeatedly and independently appeared in different, already separated branches of this family.
The nature of the emergence of evolutionary changes
Evolutionary pathways can vary. Biology distinguishes three main directions of macroevolution mentioned in classifications:
- Aromorphoses
- Idioadaptations
- General degenerations
Despite the fact that these processes lead to completely different results (ranging from an increase in organizational complexity to its simplification), the nature of their emergence is identical. Any of these changes initially arises as a regular adaptation to a specific, current environment of the organism. At the initial stage, it is impossible to predict whether this adaptation will lead to a major breakthrough or merely secure the species in its ecological niche.
Evaluation of changes in historical perspective
The main difference between the directions of evolution manifests exclusively in a historical perspective — when it becomes clear what global consequences a particular adaptation has led to.
- Aromorphoses are changes that have proven to be the most promising over time. They allow an organism not merely to survive, but to make a qualitative leap, ensuring the transition into a completely new adaptive zone (exploration of new habitats, fundamentally new food sources).
- Idioadaptations are effective, but less globally promising adaptations. They ideally solve the survival problem of a specific group, but work only within the framework of previous, familiar living conditions. They do not elevate organisms to a new level of organization, but merely specialize them.
Briefly: answers to topical questions
What is general degeneration and what are its consequences?
General degeneration represents a secondary simplification of organization, leading to the loss of organ systems and structures. This process occurs when organisms transition to a sessile or parasitic lifestyle. In a historical perspective, degeneration arises as a regular adaptation to a specific habitat. The main consequence of such simplification is that it increases the overall level of biological fitness of the group and ensures biological progress.
Specific examples of consequences:
- Loss of the digestive system in tapeworms.
- Loss of wings in lice and fleas.
- Reduction of the tail in humans.
What examples of homologous organs exist in animals?
Examples of homologous organs, developing from the same embryonic primordia and having a single structural plan, include the forelimbs of various vertebrates. These include the human forelimb, bird wing, seal flipper; the source also provides the homology of the forelimb skeleton of the salamander, turtle, crocodile, bird, bat, whale, mole, and human. These organs may differ in their functions.
The general structural plan includes:
- Humerus (humerus).
- Radius (radius).
- Ulna (ulna).
- Carpal bones (ossa carpi).
- Metacarpal bones (ossa metacarpi).
- Phalanges of the fingers (phalanges digitorum).
What specific examples of aromorphoses are characteristic of mammals?
Specific examples of aromorphoses in mammalian evolution are the hair coat, live birth, and milk feeding. Aromorphosis is a major adaptation of a universal nature that allows for the colonization of new habitats.
Aromorphoses lead to an elevation in the level of organization and are the cause of the formation of large taxonomic groups, such as phyla and classes. Initially, aromorphoses arise as regular adaptations to a specific habitat, and in a historical perspective turn out to be promising changes ensuring the transition into a new adaptive zone.
Parallelism is movement along parallel tracks: the groups have diverged (divergence), but move side by side, using identical (homologous) tools to solve similar problems.
Class and exam questions
What is the difference between parallelism and classical convergence?
Parallelism is the convergence of traits specifically in genetically close groups based on homologous organs. Ordinary convergence can also occur in completely unrelated species based on analogous organs.
How do aromorphoses and degenerations originate?
Any major evolutionary changes (aromorphoses, idioadaptations, general degenerations) initially appear as local, routine adaptations to specific environmental conditions.
How to distinguish aromorphosis from idioadaptation?
They can be distinguished only in a historical perspective. Aromorphosis ensures the transition into a new adaptive zone, while idioadaptation merely adapts the group to previous living conditions.
What else to study on this topic
- Mechanisms of formation of homologous organs
- Examples of general degenerations in nature
- The concept of divergence in macroevolution
- Colonization of new adaptive zones: ecological aspects
- Convergence based on analogous organs
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