The concept of evolution as the constant development of all living things on the planet, the complication of life forms and the emergence of its new forms is widely used today in popular literature and in the media. Speculation on the topic of evolution and microevolution, the use of the term in populist forms erodes its meaning, removing from attention the very essence of the process. What is microevolution in biology, its forms and the final result - these are the questions that are covered in this article.
Evolution as a biological process
Evolutionary doctrine distinguishes two conventional forms - macroevolution and microevolution - as mechanisms for the development of life on earth. The division is arbitrary and is based on the sizes of taxonomic units to which the evolutionary movement leads. Macroevolution involves the formation of large taxa (genus, family, class, and so on) over a long period of time. The result of microevolution is the formation of a new species, the smallest taxonomic unit. Therefore, microevolution is also called speciation, the formation of a new species in the middle of the original by achieving reproductive isolation and isolation in a separate taxon.
Patterns of development
All the laws of evolution as speciation pass in macrotaxons according to the same scenarios and according to the same rules as for the elementary units of evolution - populations. What is microevolution can be easily illustrated by the example of the formation of related, phylogenetically close species within one genus. For example, in the Arctic there are three closely related species of seals - the Witt seal, the sea leopard and the Ross seal. In addition to minor external differences, their food supply is completely different, it was they who led to the formation of closely related, but different species.
Types of Microevolution
Speciation, which leads to reproductive nonbredness as the last step in the evolutionary isolation of a group within a species, has several mechanisms. By the type of isolation mechanism , several forms are distinguished. Microevolution includes:
- Geographical speciation.
- Speciation by ecological division of populations.
- Speciation by reproductive isolation proper (pre-population and post-population).
What is geographic and environmental microevolution?
In this case, the isolation mechanism in panmictic (sexually propagating) groups of organisms is considered when a new species is formed under the influence of geographical or environmental factors. The geographical factor of isolation of populations is considered landscape changes, which lead to temporary or complete isolation of populations of the same species. A good example is the formation of island species. And perhaps the most famous in this context are the Galapagos bindweeds, the description and study of which led Charles Darwin to his theory of the origin of species. An example of what microevolution is like ecological speciation has already been cited - Arctic seals. In the case of seals, the forage base has become an environmental factor in isolation. But the ecological factor is also the mismatch of the breeding seasons, various ecological races within the species, and so on.
Pre-population form of isolation as a type of microevolution
In case of impossibility of free crossing of individuals as a result of isolation associated with the absence of the formation of a zygote (embryo) of the body, they speak of pre-populative isolation. Its forms are different:
- Isolation due to sexual behavior (ethological). An example is closely related tropical frogs, which differ in timbre and species-specificity of mating.
- Isolation caused by the various structures of copulative or reproductive organs. Example - different types of orchids have a specific flower structure, which allows them to be pollinated only by a certain type of hummingbird.
Insulation caused by mismatch of gametes. Examples are only in experiments; it is difficult to track this mechanism by nature.
Post-population isolation as a speciation mechanism
In this case, it is understood that a zygote has formed. What is microevolution in this case, the following forms of achieving complete reproductive isolation of populations within a species show:
- Zygotes viability in the early stages of ontogenesis.
- The death of a born calf or young individual before reaching reproductive age.
- Sterility of hybrids.
The biological mechanism of this form of isolation is complex and associated with cytological, biochemical and humoral characteristics.
Microevolution as a process of achieving complete reproductive isolation of a group within one species leads to the formation of new species of organisms other than parental forms. But this is in theory. Not every isolation of a population will lead to reproductive isolation, and not every reproductive isolation will lead to the formation of new forms. What dogma in evolution is that microevolution begins with isolation and ends with it.