Natural Selection : Process of Evolution – Selection

In this article, we’ll learn about the process of evolution through natural selection. Let’s begin

Introduction to Selection

Charles Darwin and Alfred Russel Wallace presented the hypothesis of evolution via natural selection in 1858. They contended that species with effective environmental adaptations are more likely to survive and reproduce than those with less useful adaptations, increasing the frequency with which good adaptations arise across generations.

Because of the limited resources available in an ecosystem, organisms of the same or different species compete for survival.

During his journey to the Galapagos Islands, Charles Darwin made numerous observations of fauna and flora. Among these discoveries was the fact that various kinds of finch colonized different islands.

On one island, the finches perfectly evolved to exist on a single food supply (e.g., insects). He hypothesized that this occurred as a result of adaptive radiation.

Natural selection is supposed to be the method through which evolution takes place. In this case, genetic diversity might result in favorable or unfavorable features.

If the organism’s traits allow it to live to reproductive age more successfully, it is more likely to outcompete other members of the population. Beneficial genes are picked and handed on to children. Unfavorable genes are targeted and may be eliminated from the gene pool.

Because of the battle for food, space, and mates, the less well-adapted individuals must perish or fail to reproduce, while the better-adapted individuals live and breed.

Natural selection may occur due to environmental causes, such as severe weather or seasonal fluctuations, without competition between species. However, artificial selection (or selective breeding) differs from natural selection in that people influence heritable differences in a species through controlled breeding.

Natural selection occurs when certain genotypes produce more offspring than others in response to environmental cues. It is a non-random shift in allele frequencies from generation to generation. Charles Darwin identified four prerequisites for evolution by natural selection in On the Origin of Species by Natural Selection (1859).

• The characteristic under selection must be changeable in the population, allowing the encoding gene to have more than one version or allele.
• The feature under consideration must be heritable, with a gene or genes encoding it.
• The battle for survival, in which many more children are born than can survive in the environment.
• Individuals with various alleles have varied survival and reproduction rates determined by the organism’s adaptation to its environment.

Natural selection occurs when the environment pressures a population, causing only particular phenotypes to survive and reproduce effectively. The higher the selective pressure or the selection event, the fewer individuals pass through the sieve of natural selection.

Those phenotypes that survive an intense selection event, like a drought, are better adapted to a drought-prone environment. So another way to put it is that they have better Darwinian fitness.

Types of Selection

Natural selection may drive change in populations in different ways depending on the kind of selection when a population has a normal distribution for a given feature.

• Stabilizing Selection
• Directional Selection
• Diversifying Selection
• Balancing Selection

Stabilizing Selection

When selecting pressures choose between two extremes of a characteristic, the population undergoes stabilizing selection. Plant height, for example, might be influenced by stabilizing selection. A plant that is too short may be unable to compete for sunlight with other plants. On the other hand, extremely tall plants may be more vulnerable to wind damage. These two selection forces work together to keep plants of medium height. As a result, the number of medium-sized plants will rise, while the number of short and tall plants will drop.

Directional Selection

In directional selection, one extremity of the trait distribution is targeted for selection. As a result, the population’s trait distribution swings to the opposite extreme. The mean of the population graph alters as a result of such selection. Using the well-known example of giraffe necks, there was selection pressure against short necks since individuals with short necks could not reach as many leaves to graze on. As a result, the distribution of neck length has moved in favor of those with long necks.

Disruptive Selection

In disruptive selection, selection forces occur against individuals in the middle of the trait distribution. As a result, the curve is bimodal, or two-peaked, with the two extremes creating their own smaller curves. For example, consider a plant with a wide range of heights that is pollinated by three separate pollinators, one of which is drawn to short plants, another to medium-height plants, and a third to the tallest plants.

If a pollinator that favored medium-height plants disappeared from a region, medium-height plants would be chosen against, and the population would choose both short and tall plants, but not medium-height ones.

Balancing Selection

When numerous phenotypes (or alleles) are actively maintained in the population, this is called balancing selection (i.e., no single phenotype has a consistent selective advantage over any other).

The two most prevalent types of balancing selection are frequency-dependent selection, in which fitness is determined by how common the phenotype (or allele) is, and heterozygote advantage, in which the heterozygote (with the combined phenotype of both alleles) outperforms any homozygote.

Sexual Selection

The mutual attraction between the sexes is a key component in reproduction. Males and females of many animal species are comparable in size and form, except for sexual organs and secondary sexual features, such as female mammals’ breasts. There are, however, animals in which the sexes demonstrate remarkable dimorphism.

Organisms that are better at attracting mates have higher fitness. Two general factors lead to sexual selection. One is a preference displayed by one sex (usually females) towards persons of the other sex who exhibit particular features. The other is improved strength (typically among males), which results in better success in attracting mates.