Principles of Evolutionary Biology and Natural Selection

Darwin’s Theory of Evolution

Darwin’s theory posits that the world is not static; it is constantly changing. The process of change is gradual and continuous, and similar organisms are related and descended from a common ancestor. Evolutionary change is the result of natural selection.

The Mechanism of Natural Selection

Darwin explained natural selection through the following principles:

• In any population, individuals have variations, which are produced randomly.
• In the fight for existence, only the fittest survive.

Darwin’s explanation for this fact is that, when resources are limited, individuals in a population must compete for them. In this fight for existence, only those with favourable variants survive, as they are best adapted to the environment.

Natural selection is the process that favours those individuals best adapted to the environment, which, over time, leads to the appearance of new species.

Neo-Darwinism and Modern Genetics

Neo-Darwinism is a revision of Darwinism, enriched by the contributions of modern disciplines such as genetics, and advances in palaeontology and taxonomy.

The contribution of genetics: The discovery of the laws of inheritance of genes and the processes of mitosis and meiosis explained how hereditary variations are transmitted and defined what causes them:

• Genetic recombination during meiosis.
• Mutations cause changes in genes.

Natural selection favours genotypes for favourable traits in certain environmental conditions. However, a change in these conditions will favour different traits and, through the process of natural selection, genotypes for these traits will become more frequent in the population.

Punctuated Equilibrium

The theory of punctuated equilibrium is a refinement of Neo-Darwinist gradualism, which explains sudden evolutionary changes observed in the fossil record. It suggests that there are occasional periods of intense speciation, which occur after major events, such as geological catastrophes. In periods when environmental conditions are relatively stable, there is little evolutionary change. In other words, the evolutionary process takes place in leaps.

Key Evolutionary Concepts

• Adaptation: The accumulation of advantageous traits within the members of a population.
• Speciation: The mechanism that creates new species from previous ones.