Issues of ecology, evolutionary theory, population biology, and other sciences often touch upon the concept of variability (both definite and indefinite). This is the cornerstone for understanding the origin of species, their ability to adapt to changing environmental conditions. These principles underlie modern selection and molecular biology. Let's try to figure out what these concepts mean.
Types of variability
These concepts are also called hereditary and hereditary variation. What is the difference between definite and indefinite variability? The first arises in a group of individuals as a response to external factors. It is regulated by the magnitude of the reaction rate. As an example, you can recall the hibernation of a bear, the density of the dog’s coat, the length of the stem of a dandelion. If you change the environmental conditions, then these signs may not appear. So, if you artificially create an abundance of food and a warm temperature year-round, then the bear will not sleep for the winter. A dog that lives inside the house in winter will have much less undercoat than a chain yard dog. With a constant mowing of the lawn, the dandelion will grow with a shorter stem length, which will allow it to form a peduncle and avoid cutting. Of course, such traits are not genetically inherited.
Hereditary variation arises as spontaneous mutations within a group of individuals and is inherited through generations. However, not all mutations are useful. Most of them become useless or harmful. Only a few changes will be supported by natural selection. This property is the basis of evolution, as it allows the body to adapt to changes in the environment, to acquire qualities that contribute to survival. Let us dwell on this type in more detail.
History of the Study of Uncertain Variability
When mentioning the factors affecting the origin of species, one cannot fail to mention the author of the eponymous book and theory of evolution, Charles Darwin. Of course, to date, this theory has been finalized and is called synthetic. However, the description of the basic concepts and principle remained unchanged.
According to Darwin, uncertain variability is "infinitely diverse minor features that distinguish individuals of the same species and which cannot be explained by inheriting them from one of the parents or from more distant ancestors." He also spoke about the direct and indirect influence of the conditions of existence on the formation of a living organism, about the correlation of signs. Moreover, the concept of a gene did not yet exist, and the reasons for the appearance of these features were not clear to this scientist. It is now known that inheritance is of a genetic nature, and mutations occur in DNA constantly.
How does this mechanism work?
DNA replication constantly causes errors. Normally, they should be removed by the immune system or the cellular apaptosis system (programmed death). In case of failure of these systems, this cell can survive and create its own copies. If the body is unicellular or changes affect the germ cells, this defect will be inherited and transmitted to other generations. This creates a diversity of the population and guarantees the survival of the species and evolution as a whole.
Types of Mutations
- Gene. Affect the structure of DNA at the nucleotide level. Expressed in the loss, replacement of a nucleotide (as an example, human diseases, such as phenylketonuria, sickle cell anemia).
- Generative. Genes of germ cells are affected. Inherited through generations.
- Somatic. Mutations of non-sex cells. In animals, they are not inherited, but in plants they are inherited during propagation using the vegetative method (in cell culture in vitro).
- Genomic. Associated with a change in the number of chromosomes in the nucleus. They can manifest themselves as an increase of one or several chromosomes (in humans, Down's disease is associated with an additional chromosome) and as a multiplication of their number (polyploid plants are indicative: most modern wheat varieties are octoploid, i.e. they have eight sets of chromosomes).
- Chromosomal
Value
- The species does not constantly live in the same conditions. In the event of a change in living conditions, sometimes abrupt, for example, due to a natural disaster, migration to another continent, etc., the entire population may undergo extinction. But some organisms may have mutations, up to this point they are useless, and now they are necessary for survival. This means that only these individuals will survive and give birth already with these traits. An example would be the constant fight "bacteria - antibiotics". The developed antibacterial agents are quite effective for a certain time until the offspring of microorganisms with resistance genes for this type of medication multiply. This forces the pharmaceutical industry to create new tools and unwittingly stimulate bacteria to further evolution.
- The value in the selection. It was this type of variability that Charles Darwin considered the basis for artificial selection. Mutations that initially appeared regardless of environmental factors can be valuable to humans. So, for example, large-fruited tomato fruits are not useful for the plant itself - the branches will not withstand their weight without supports and garters. But selection on this basis allowed to obtain more productive varieties.
Definition: What is Uncertain Variability in Biology?
Summing up the above, we summarize what this concept means in science. Uncertain variability in biology is a concept synonymous with mutations. It is hereditary (in contrast to a certain one), while minor changes in the genome in the first generation accumulate and intensify in subsequent ones. This type of variability is also associated with changes in environmental factors, but not in the form of adaptations, but indirectly. Thus, it helps to adapt not to a specific organism, but to the taxon as a whole.
Examples of Uncertain Variability
Earlier in the article, private examples of mutations that help adapt to the environment were discussed. Consider several broad types of such variability in nature:
- Protective coloration. It occurs in many animals. In the process of natural selection, individuals that are more inconspicuous in the surrounding landscape are less susceptible to attack by predators and, therefore, can give more offspring. This feature is fixed in generations. In this case, when environmental conditions change (for example, when a population moves to another habitat), the color supported by selection may change.
- Signal coloring. As a result of changes in the genome, some insects have acquired a bright color, warning predators about toxic glands. Non-toxic insects can also have this color, this protects them from eating. This phenomenon is called mimicry.
- Body shape. The indirect influence of the environment supports individuals whose body shape is most adapted to it. So, a torpedo-like shape that helps in swimming is characteristic of aquatic organisms. It is similar in dolphins, seals, penguins, fish, swimming beetles. Naturally, this form in these animals developed independently. It’s just that in the process of evolution those individuals who were best suited for swimming survived and gave offspring.
- Protective mechanisms. For example, the needles of a hedgehog, porcupine - a modified hairline. Individuals that received, due to spontaneous mutation, a denser stubble that can cause inconvenience to a predator, gained an advantage in reproduction. In the next generations, it was most likely that the selection of the wooliness was supported by selection - this feature intensified.
Summarizing
This type of variability does not guarantee the survival of the organism, but ensures the survival of the species in constantly changing environmental conditions. Uncertain variability is necessary for humans as a tool for breeding work. It contributes to the natural and artificial origin of new taxa. That is why vague variability is the basis of evolution.