Natural Selection: Definition, Types, Examples and Process

What Is Natural Selection?

This type of evolution states that the average traits of the population change over generations because new organisms with genetically favourable traits are more likely to live longer, produce offspring and pass the traits on to successive generations. Such processing causes the transition in species towards having new characteristics favorable for survival in various environments thus resulting in the evolutionary development.

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The idea of natural selection stems from the work of Charles Darwin in the 1800s which brought a new way of thinking concerning species development. Darwin introduced the theory of evolution in a book entitled “On the Origin of Species” and it offered a background to why and how existence comprises variation and organisms change their traits due to survival of the fittest and reproduction of the strong ones.

Key Concepts Of Natural Selection

Knowledge of the following concept is important to understanding natural selection

Variation

The populations need genetic variation since it is one of the key components of natural selection and serves as the starting point for evolution. Variance arises from mutation, a conception that generates new alleles; gene flow that transplants… alleles; and sexual reproduction which rearranges alleles.

Inheritance

Certain conditions must be met for natural selection to occur; the first of these is heritability, by which the characteristics have to be inherited from the parents to the young. This concept is based on Mendelian genetics which focuses on the way traits are passed from one generation to another by genes and their variants.

Differential Survival And Reproduction

From the view of natural selection, there is differential survival and reproduction; those with helpful inducements have higher chances of survival as well as reproduction. Some examples of such principals are found in antibiotic-resistant bacteria, or beak size in Darwin’s finch where the strongest and fittest one survives.

Adaptation

Adaptation is also the characteristics that Increase the opportunity for the organism to survive and reproduce in a particular environment. These traits occur or change due to any environmental pressure that may exist like predation or climate and could also be illustrated in instances of peppered moths that adapted to tree trunks, and the long necks of giraffes to reach high foliage among others.

Mechanisms Of Natural Selection

The mechanism of natural selection includes:

Directional Selection

Directional selection takes place when there are demands from the consideration that one of the extremes of the phenotypic variation possesses better adaptation for the environment as related to the rest of the population. For instance, the change in beak size, the finches of Darwin where bigger beaks were preferred during a drought for cracking seeds.

Stabilising Selection

A mechanism of stabilizing selection removes variation and supports the preservation of the traits’ middle value. An example is human birth weight, that the two extremes of high and low birth weight have lower probabilities of survival than average weight.

Disruptive Selection

Disruptive selection results in the fixing of two highly divergent individuals at both ends of the scale of variation thus increasing the variation and possibly even speciation. One can easily think of situations like the one in which the size of the beak of the bird is a plus and minus to the extent that small birds which eat small seeds will naturally have very small beaks while other birds that eat large seeds will have very large beaks.

Sexual Selection

Sexual selection is a type of natural selection in which characteristics become favoured for reasons other than enhancing the likelihood of the bearer’s survival but rather to enhance his/her chances of finding a mate. Some instances include; the appearance of a male peacock, where its feathers are designed to attract females or the large antlers of the male deers intended for the same purpose.

Evidence For Natural Selection

The evidence of natural selection is found in these sources:

Fossil Record

The other evidence of evolution comes from the analysis of fossils and their ages, which gives chronological evidence for evolution. Some of such include the Archaeopteryx which has characteristics of both the reptiles and the birds thus demonstrating a link of evolution. Interpretation: These fossils show changes in species with one being an evolution of the other and therefore supporting the idea of common ancestry.

Comparative Anatomy

Homologous and analogous organs help to establish the relation between the species in the field of comparative anatomy. Accessory structures such as limbs of vertebrates, though present with different functions, are evolutionary products of the same structure while analogous structures like wings of insects and birds even though they have the same function have evolved with a different beginning. The existence of organs like the human appendix that have no significant function in the current organism but had a functioning part in the ancestor species points to evolution.

Molecular Biology

Molecular biology provides evidence for natural selection by revealing via the DNA sequence evidence that linked different species; have a common ancestor. The second one is protein and genetic relatedness also support the findings of evolutionary relatedness; closer related species possess higher sequence comparisons meaning that they will have similar DNA sequences and protein structures.

Observed Instances Of Natural Selection

• Antibiotic Resistance in Bacteria: Bacteria grow resistance against antibiotics through mutations and selection which explains that potential forces of evolution take place.

• Industrial Melanism in Peppered Moths: The Industrial Revolution led to pollution which darkened the tree barks; this is an example of natural selection where the population of dark-coloured moths was on the rise.

• Darwin’s Finches: This is especially seen through observations that were made regarding the differences in beak size of finches in the Galápagos Islands, which show that when under pressure of certain conditions, certain characteristics are selected.

Case Studies And Examples

Some most common examples of natural selection are:

Galápagos Finches

One of the reasons was Darwin’s observations regarding the finches living in the Galapagos: concluded digitalis that changes in the shape of beaks, which differently on different Islands, are suitable for feeding on different species of food.

Significance: The adaptations already mentioned are great for emphasizing natural selection and adaptive radiation because they illustrate how species are developed depending on pressures.

Peppered Moth

That colours ranging from light to dark are part of a single species is a perfect example of industrial melanism.

Significance: The changing colour of the industrial moth from dark in the Industrial Revolution probably due to the effect of pollution and later becoming light as pollution was reduced is an excellent example of evolution due to adaptation.

Antibiotic Resistance In Bacteria

Bacterial, resistance to antibiotics shows natural selection in bacteria in as much as mutations and gene transfer enable the bacteria to survive the antibiotic.

Significance: This resistance presents overall threats to public health, and therefore it requires the precautionary use of antibiotics for eradication of resistant strains.

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