A modern educated layman will not argue with the fact that the development of life on our planet follows evolutionary laws. And the “screenwriter" of this process, the result of which was the entire species diversity of living organisms, is natural selection. Any of its forms (stabilizing, moving and disruptive selection), examples of which nature continues to supply, surprises and bewitches. In the article, we briefly present the main characteristics of the driving factors of evolution and examples of speciation. We also give examples of natural selection, the disruptive form of which is a combination of the stabilizing and motor forms, leading to polymorphism within the species.
The "screenwriter" of evolution
The evolution of life, its diversity, comes down to the processes of microevolution or speciation. But not all evolutionary processes in populations end in the formation of a new species. While the emergence of new species always begins with evolutionary mechanisms within the species - the appearance of phenotypic diversity (polymorphs) as a result of mutations, isolation of populations and the action of natural selection - the differentiated reproduction of certain phenotypes that will be most adapted to the given environmental conditions. It is selection that becomes the driving force that will determine how many and which individuals will be successful in the struggle for survival, will survive to reproductive age and will be able to leave the largest number of fertile (capable of subsequent reproduction) offspring.
Forms of natural selection
From the direction of adaptive changes will depend on which way selection will go and who will be the winner in the struggle for survival. In evolution, there are three forms of natural selection:
- An example of disruptive selection is the preservation in populations of oceanic islands prone to strong winds, insects or with large wings, or generally wingless.
- This selection eliminates the middle peasants, giving advantages to the rearguard and outsiders. It is disruptive selection, examples of which will be given in this article, that is the result of the combined action of stabilizing and moving selection, acting alternately.
- Driving (directed) selection reinforces new forms that are more in demand in the changing environment. In this case, the old forms are eliminated from the population. For example, the loss of fingers in ungulates. It is this type of selection that does not allow us to defeat bacterial infections - the bacteria adapt very quickly to the effects of antibiotics and we have to invent more and more new drugs.
- Stabilizing selection comes into play when environmental conditions are unchanged and its goal is to maintain the average peasants. This form of selection is most common in nature. She hones devices, bringing them to maximum efficiency. For example, in severe winters, sparrows with average wing sizes survive, while long-winged and short-winged are less successful in the struggle for survival.
Sexual dimorphism
An example of disruptive selection in action is sexual dimorphism in most panmactic (sexually reproducing) animals. External differences between females and males within a species are far from always justified and often do not help animals to better adapt to environmental conditions. But it is precisely by such tearing selection that these differences formed in the process of evolution.
Male peacocks are an example of an animal whose disruptive selection within a species is almost absurd. Their huge tails are needed only during the breeding season, while for the rest of their lives they are more likely to harm their owners. Deer horns, the bright plumage of males of tropical birds, also turn out to be not particularly advantageous. There are quite a lot of theories of pinning precisely the signs of sexual dimorphism. But all of them basically rely on disruptive selection tearing the population.
Polymorphism is the norm for the species
Most species in nature have many phenotypic forms (morphoforms), which are an example of disruptive selection. A homomorphic population is less likely to adapt to environmental changes. Examples and characteristics of disruptive selection in nature are diverse and numerous. There are polymorphs in populations according to phenotypic, biochemical, ethological and environmental characteristics. Thus, the presence of early flowering and late flowering forms of many meadow herbaceous plants can serve as an example of disruptive selection in plants. Especially those that grow in meadow ecosystems. The meadow rattle usually blooms all summer, but two morphoforms of this plant appear on grasslands - one blooms before haying, and the second after.
Different snails
A striking example of disruptive selection in animals is the variety of colors of the shell of earthen snails. This example is described in all textbooks: in snails in the forest zone, the shell is brown or pink, in snails in glades with yellow grass and shells are yellow. Snail polymorphism is a purely adaptive feature that does not give particular advantages to any morphoform.
Another example of disruptive selection is the water snakes of North America. Shore snakes have wide transverse dark stripes on a light background, island snakes - more often without stripes at all and have a lighter general background. This is a purely adaptive adaptation - monophonic snakes are less visible on the rocks of the islands. But hybrids of these morphoforms are extremely rare - because they are not adapted neither to life on the river bank, nor to life on the rocky islands.
Colorful frogs
Characterization and examples of disruptive selection prove the existence of polymorphs in a population and the lack of advantages of these forms over each other. Thus, this form of selection stimulates intraspecific diversity and, under certain conditions, can become material for the formation of new species. So, lake frogs are found in two phenotypes - with a predominance of green in color or brown. It all depends on the habitat. Under certain conditions, both morphoforms can become the initial link in speciation. The same polymorphism is clearly visible in populations of ladybugs or variegated birds. But the evolutionary process is quite lengthy and it is not so simple to observe it in action.
Tearing selection in action
You can observe the effect of disruptive selection on the example of predatory fish in a low-feed reservoir. Often, small pikes do not have enough food in the form of fry, and then fish with very fast growth receive advantages, which allows them to hunt for larger victims. Either the squint with a growth retardation will benefit - they will be able to feed on planktonic crustaceans longer. In such closed lakes, the formation of two pike morphoforms is quite possible - either very large or very small.
The interaction of disruptive and driving selection can be illustrated by the phenomenon of industrial melanism (various colors of butterfly wings in clean and polluted areas), which is described in more than 70 species of various insects. This case is most vividly illustrated by the birch moth, which has white wings in nature. But in contaminated areas, the color of its wings becomes almost black. Interestingly, when conditions change, the wings of butterflies in the population brighten. Thus, industrial melanism is another example of disruptive selection that leads to polymorphism.
What about us?
It would seem that what can be in common with pikes in a pond and us humans? It turns out that it is also possible to find an example of the action of the disruptive form of natural selection in our society. The theory of corporate management explains this very selection by creating new revolutionary businesses and capturing unreached markets. In organizations with disruptive selection, leaders are born who recruit their own teams from their own kind, cutting off the middle peasants. So there are new directions, subsidiaries and revolutionary startups. “Disruptive Leaders” are expansive, maximized people. They are the ones who start the business and seize the bridgehead.
Leadership Strategies from Evolutionary Biology
Then they are replaced by “moving leaders” - the staff is growing, success is developing and consolidating. The next stage in the development of an organization is stabilizing or stagnation. The increased number of employees becomes an anchor, reducing the dynamics of business development. Then comes either a gradual fading, the departure of the middle peasants and the collapse of the company, or the transition to a disruptive leadership strategy. Here is a decision-making system as a product of natural selection in the management of organizations. Of course, very simplified, but this is the topic of another article.