Properties of living systems as the basis of evolution
Living organisms are open systems that exist through the continuous exchange of matter and energy with the environment (including processes of absorption, secretion, filtration, and excretion). Their key properties are inextricably linked to the evolutionary process:
- Self-reproduction and heredity rely on genetic information in DNA, ensuring the continuity of species over time.
- Variability allows for the acquisition of new traits during individual development, creating raw material for natural selection.
- Irritability forms the basis of the primary adaptation of organisms to changing conditions.
- Growth and development are realized in two forms: individual (ontogeny) and historical (phylogeny).
To maintain the stability of chemical composition and physiological processes, organisms use self-regulation — homeostasis (from Greek homoios — similar, stasis — stationary).
Development of evolutionary views
For a long time, the ideas of the immutability of nature dominated science. John Ray was the first to formulate the biological concept of the "species," and Carl Linnaeus created a convenient hierarchical classification and binomial nomenclature. By placing humans in the order Primates based on morphological traits, Linnaeus indirectly paved the way for future discoveries, although he himself believed in the divine creation of species.
The first evolutionary concept was proposed by Jean-Baptiste Lamarck. He believed that species do not actually exist, and only individual entities change under the influence of the environment and an internal drive for perfection. A genuine breakthrough was made by Charles Darwin, who proved the reality of species as stages of historical development and identified natural selection as the main driving force.
In the 20th century, Sergei Chetverikov combined Darwinism with genetics, laying the foundations of the modern synthesis (synthetic theory of evolution). Later, Ivan Schmalhausen substantiated the unity of micro- and macroevolutionary mechanisms based on the theory of stabilizing selection.
Factors and forms of natural selection
Evolution relies on elementary factors: mutation process, isolation, population waves, genetic drift, and the struggle for existence. The main guiding mechanism is natural selection, which operates in three main forms:
| Form of selection | Mechanism of action | Result and examples |
|---|---|---|
| Directional | Shifts the average trait norm when environmental conditions change | Reduction of eyes in the mole, industrial melanism in butterflies |
| Stabilizing | Preserves the norm under constant conditions, pruning extreme deviations | Survival of relict species (tuatara), average birth weight of infants |
| Disruptive | Supports extreme variants while culling intermediate values | Emergence of human races, flightless insects on islands |
Pathways of speciation and macroevolution
The increase in biological diversity occurs through cladogenesis (from Greek clados — branch, genesis — origin) — the process of splitting one phyletic lineage into several daughter lineages (divergence). At the level of large taxa, this is described by Henry Fairfield Osborn's rule of adaptive radiation: the ancestral trunk yields a "fan" of lineages exploiting different ecological niches.
A classic example of cladogenesis is allopatric (geographic) speciation. It begins with the appearance of a physical barrier. Mutations accumulate in isolated populations, and reproductive isolation eventually arises. As Theodosius Dobzhansky noted, it is precisely isolating mechanisms that transform a genetically open population into a closed system — a new species.
In contrast to cladogenesis, there is anagenesis (phyletic evolution) — the gradual transformation of one species into another over time without an increase in the total number of species. Also, new forms can arise via hybridization (hybridogenous speciation, often through polyploidy in plants).
To avoid confusing the forms of phylogeny, use visual associations: Divergence — Tree (branches diverge, forming homologous organs), Convergence — Wedge (lines converge at a single point due to the environment, organs are analogous), Parallelism — Parallel lines (independent development in related groups).
Class and exam questions
What is the difference between microevolution and macroevolution?
Microevolution proceeds at the population level and culminates in the formation of a new species. Macroevolution forms supra-species taxa (genera, families, orders), but according to the modern synthesis, it relies on the same basic mechanisms: mutations, selection, and isolation, only on a larger time scale.
What is the rule of adaptive radiation?
This is a manifestation of cladogenesis at the level of large supra-species taxa. A single ancestral trunk diverges into different adaptive directions, and each new lineage specializes in its own unique ecological niche.
What is the role of isolation in speciation?
Isolation creates barriers that prevent free interbreeding (panmixia) between individuals. It solidifies accumulated genetic differences, ultimately turning the population into a new, reproductively isolated species.
What else to study on this topic
- Mechanisms of sympatric speciation without geographic barriers
- The role of disruptive selection in the formation of heterozygous polymorphism
- Automation of ontogeny during progressive evolution (according to I.I. Schmalhausen)
- The impact of population waves and genetic drift on allele frequencies
- Hybridogenous speciation and polyploidy in plants
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