Severtsov's Doctrine
The foundation for understanding the main pathways of the organic world's development is the doctrine formulated by A.N. Severtsov in 1925. The scientist was the first to clearly distinguish between the concepts of progressive and regressive historical development. Within his theory, two key concepts were strictly substantiated and separated: biological and morphophysiological levels of evolutionary change. This allowed biologists to understand that an increase in anatomical complexity is not the sole measure of success in living nature.
In the course of evolution, forms may follow different trajectories, but the ultimate goal of any large-scale changes boils down to one thing—the survival and dominance of the group. The distinction introduced by Severtsov explains why both highly complex organisms and forms with an extremely primitive organization simultaneously exist and thrive in nature.
Biological Progress
Biological progress refers to the global evolutionary success of a particular group in the continuous struggle for existence. This state means that a species or a larger taxon is ideally adapted to current environmental conditions, and its overall fitness continues to steadily increase.
According to Severtsov's doctrine, to establish the presence of biological progress, three main indicators must be recorded:
- Constant increase in the number of individuals — birth rate and survival significantly exceed mortality.
- Expansion of the habitat range — the group successfully colonizes new territories and ecological niches.
- Increased rate of intraspecific differentiation — active formation of new populations, subspecies, and species within the group in question.
Morphophysiological Changes
Biological progress can be achieved through completely different pathways at the anatomical and physiological levels. Severtsov identified two opposite directions of structural transformations:
- Morphophysiological progress. This is the classic increase in the general level of organization. In this case, the structure of the organism and its vital activity systematically change from the simplest forms to more complex and perfected ones.
- Morphophysiological regression. This is a radical simplification of the level of organization and vital activity. This pathway is mainly expressed in the profound reduction of organs that have lost their significance for survival. Despite the apparent "degradation", this process can also lead to biological prosperity and victory in the struggle for existence.
Parallel evolution
A special direction of evolutionary change is parallel evolution. This process is characterized by the formation of a strikingly similar external appearance in groups of organisms that were initially divergent (descended from a common ancestor) but remained genetically very close.
This phenomenon is often called parallelism. It is important to understand that parallelism represents a specific convergence based strictly on the development of homologous organs. A classic example of parallel evolution is the repeated, independent development of the saber-toothed trait in various evolutionary branches of the single felid lineage.
Briefly: answers to topical questions
What is biological regression and what indicators characterize it?
Biological regression is a decrease in the level of adaptation to environmental conditions. Characteristic signs of this process include:
- Decrease in population size — a reduction in the number of individuals in the group.
- Range contraction — a reduction or fragmentation of the habitat range.
- Elimination — mass catastrophic mortality.
- Extinction — the complete disappearance of a group.
What three main pathways for achieving biological progress (aromorphosis, idioadaptation, degeneration) did A.N. Severtsov identify?
Biological progress is achieved through agenesis, allogenesis, and catagenesis.
- Agenesis — progressive evolution carried out through aromorphoses (major changes that raise the general level of organization).
- Allogenesis — evolution via idioadaptations (particular adaptations to specific environmental conditions without raising the general level of organization).
- Catagenesis — evolution via general degeneration (simplification of organization), allowing a group to adapt to new conditions and spread widely.
What is convergence in evolution, and upon the development of which organs is it based compared to parallelism?
Convergence is the convergence of traits in unrelated groups under similar conditions.
| Process | Organs | Characteristic |
|---|---|---|
| Convergence | Analogous organs | Convergence of traits in unrelated groups |
| Parallelism | Homologous organs | Independent development of similar traits in closely related groups |
To memorize the three signs of biological progress, use the acronym "SAD": Size (population increasing), Area (range expanding), Differentiation (increasing).
Class and exam questions
What is the essence of biological progress?
This is the evolutionary success of a group in the struggle for existence, which is expressed by an increase in the number of individuals, expansion of the geographic range, and active intraspecific differentiation.
How does morphophysiological progress differ from regression?
Progress implies an increase in the complexity of structures and life processes from simple to complex. Regression, by contrast, is expressed in the simplification of organization and the reduction of organs.
What is parallelism in biology?
This is the formation of a similar appearance in genetically close, yet diverged groups. The process represents convergence based on homologous organs.
What else to study on this topic
- Mechanisms of formation of homologous organs in parallelism
- Factors stimulating intraspecific differentiation
- The relationship between biological progress and morphophysiological regression
- The role of the struggle for existence in A.N. Severtsov's concept
Master the entire topic in the "Biology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Directions of Evolution" and 3,793 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 129 video lessons on the subject
Other topics in the section "Main Pathways and Directions of Organic Evolution"
The entire section "Main Pathways and Directions of Organic Evolution"Free video lessons: BiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.