History of the theory and the principle of unity of mechanisms
The term was introduced into scientific use by the Soviet biologist and geneticist Yuri Alexandrovich Filipchenko (1927). Subsequently, the theory of macroevolution grew out of fundamental research by a constellation of prominent scientists: I.I. Schmalhausen (1939), A.L. Takhtajan (1943), G. Simpson (1944), and B. Rensch (1947).
A major breakthrough was the substantiation of the principle of unity of micro- and macroevolutionary mechanisms, first clearly formulated by Ivan Ivanovich Schmalhausen. This thesis logically follows from his theory of stabilizing selection. The scientist proved that macroevolution is based on the same elementary evolutionary factors. The main difference is that at the supraspecific level, the nature of mating changes cardinally—complex interspecific relationships arise and become fixed.
Schmalhausen's works became an example of a grand scientific synthesis. He combined the principles of genetics with data from several biological disciplines at once:
- Comparative anatomy;
- Embryology;
- Biogeography;
- Paleontology.
According to his conclusions, during progressive evolution, population-genetics and macroevolutionary components are closely intertwined, leading, in particular, to the automation of ontogeny.
Methods of studying macroevolution
The specifics of studying supraspecific transformations are dictated by colossal temporal scales. Since the processes of genus and family formation take millions of years, they cannot be reproduced or observed experimentally.
Because of this, researchers are forced to rely exclusively on descriptive methods. A complete picture of evolutionary changes is reconstructed by integrating data from various sciences:
- Paleontology;
- Embryology;
- Biogeography;
- Comparative anatomy and morphology;
- Ethology and physiology.
Only through analysis at the macroevolutionary level using the full range of these disciplines do biologists manage to identify general trends and global patterns in the development of the organic world that are invisible over short time spans.
The role of neoteny in evolution
One of the critically important macroevolutionary mechanisms is neoteny—the evolutionary shortening of individual development, in which the adult organism retains juvenile (childhood) morphological traits.
The significance of neoteny for evolutionary progress has been proven by several prominent scientists:
- N.K. Koltsov established that this phenomenon is extremely widespread in the animal kingdom and critically important for progressive evolution. The paradox of neoteny lies in the fact that this process leads to a visible morphological simplification of body structure, yet fully preserves the genetic wealth (genotype complexity), opening pathways for new rearrangements.
- J.B.S. Haldane Jr. argued that the largest evolutionary events could have arisen precisely as a result of neoteny. As a classic example, he cited the origin of man, metaphorically calling him a "naked ape" that retained the traits of primate offspring into adulthood.
Briefly: answers to topical questions
What elementary evolutionary factors underlie both micro- and macroevolution?
Both macroevolution and microevolution are based on the same probabilistic processes that serve as sources of intrapopulation variability. Two groups of factors are distinguished:
- Main factors—mutation process, population waves, isolation, and natural selection. They ensure the appearance of new alleles, chromosomes, and sets of them.
- Additional factors—migration (gene flow) and meiotic drive. They alter allele frequencies and the genetic structure of the population.
The difference between macro- and microevolution is that in macroevolution, the nature of mating changes and interspecific relationships arise.
What are the main forms or directions of macroevolution?
The main forms of phylogenesis are divergence, convergence, and parallelism.
- Divergence—the divergence of traits in related groups; associated with homologous organs.
- Convergence—the convergence of traits in unrelated groups under similar conditions; associated with analogous organs.
- Parallelism—the independent development of similar traits in closely related groups.
Sources also indicate:
- Allogenesis (idioadaptation)—an evolutionary pathway in which specific adaptations to particular environmental conditions arise without increasing the general level of organization.
- Aromorphosis (arogenesis)—a major evolutionary change leading to an increase in the general level of organization and vital activity, allowing organisms to colonize new environments.
What main empirical rules describe the patterns of macroevolution?
The patterns of macroevolution are described by the rule of irreversibility of evolution and the rule of descent from unspecialized ancestors.
- Rule of irreversibility of evolution (Dollo's law)—phylogenesis as a whole is irreversible. An organism cannot return to a state already passed by its ancestors, even if it returns to its former habitat.
- Rule of descent from unspecialized ancestors (Cope's rule)—new major taxonomic groups originate from relatively unspecialized ancestral forms. Such forms possess greater evolutionary plasticity and can give rise to new branches with fundamentally new adaptations.
For quick memorization of basic descriptive methods in studying macroevolution, the acronym PEBS can be used: Paleontology, Embryology, Biogeography, Comparative anatomy.
Class and exam questions
What is the main difference between the mechanisms of macroevolution and microevolution?
It is based on the exact same elementary evolutionary factors. The main difference lies in the altered nature of interbreeding and the formation of interspecies relationships.
Can macroevolution be studied experimentally?
No, experimental study of macroevolution is impossible due to the enormous time scale (millions of years). Only descriptive methods are applied.
What is neoteny and what does it lead to?
This is the retention of juvenile traits in an adult organism. It leads to morphological simplification, but preserves the richness of the genotype, making it an important factor in progressive evolution.
What else to study on this topic
- I.I. Schmalhausen's theory of stabilizing selection
- Automation of ontogeny in progressive evolution
- The connection between neoteny and anthropogenesis (the "naked ape" theory)
- Elementary factors of microevolution and their transfer to the macro level
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