What is the theory of evolution?

Tree of Life

The theory of evolution, in its current form, asserts that the transformation of species (the evolution of life) depends on five factors:

1.      Spontaneous variations in the genome (mutations, genetic recombination, and other events that modify the genome).

2.      Spontaneous variations in the environment. This factor is often overlooked, as the environment is usually quite stable, although sudden changes sometimes occur that can have huge consequences.

3.      Inheritance, through which the variations that occur as a result of the first factor are passed on to offspring and are subject to the action of natural selection.

4.      Natural selection, which means that those individuals whose genome is best adapted to the environment will leave more offspring (at least statistically).

5.      The basic laws of the universe, which are currently represented by quantum theory and the theory of relativity.

Darwin’s contribution consisted in proposing the existence of the fourth factor (natural selection), assuming the existence of the first three, although he did not understand their mechanisms. Those of heredity (the third factor) were discovered by Gregor Mendel during Darwin’s lifetime, although they remained almost unknown to the scientific community until their rediscovery in 1900. Mutations were discovered by Hugo de Vries in 1901. With these advances, the theory of evolution was complete by the beginning of the 20th century. As for the fifth factor, it is not usually mentioned, but recently it has been given greater importance with the discovery that the laws of the universe appear to be finely tuned to make life and its evolution possible.

The first two factors are what Jacques Monod called chance in his book Chance and Necessity. The third (heredity) is necessity. The fourth (natural selection) is just the statistical observation that better-adapted individuals tend to leave more offspring.

Theodosius Dobzhansky

Around 1930, Theodosius Dobzhansky, Ernst Mayr, George Gaylord Simpson, Ronald Fisher, J.B. Haldane, Sewall Wright, and other biologists formulated the synthetic theory of evolution, or neo-Darwinism, which applies Darwin’s ideas to populations of living beings rather than isolated individuals. This theory remains dominant today, although it has undergone minor revisions. The main ones are:

• Richard Dawkins’s selfish gene theory, which holds that evolution applies to genes and that individuals are merely instruments used by genes to reproduce. This theory is now dubious because it is based on the central dogma of molecular biology, proposed in 1958 by Francis Crick, one of the discoverers of the structure of DNA, which is now considered an approximation rather than a dogma.
• The neutralist theory of evolution, proposed in 1968 by Motoo Kimura, which asserts that slightly detrimental genes may remain marginally present in a population, and if the second factor (the environment) changes and those genes become favorable, their prior existence in the population accelerates adaptation to the new conditions.
• The punctuated equilibrium theory, proposed in 1972 by Stephen Jay Gould, which states that long periods of evolutionary stagnation can be followed by short periods of extremely rapid change. This happened, for instance, when life underwent a change in level, such as what led to the Cambrian explosion, or when the environment changed abruptly and mass extinctions occurred, such as what happened at the end of the Permian period, which was followed by the diversification of reptiles, and what happened at the end of the Cretaceous period, followed by the diversification of mammals. This explains the problem of macroevolution, which is sometimes presented as an argument against the theory of evolution, and which turns out to be a false problem, since it does not require special mechanisms and can be explained in terms of HOX-like genes and the number of empty ecological niches at a given time.

In one of my books, The Fifth Level of Evolution, I have explained the past changes in the level of life (four changes have taken place so far, plus an incipient fifth level); I have pointed out that a direction in evolution can be seen and measured; and I have indicated where it might lead us in the future, the endpoint of which I identify with an idea that, in some way, has been known for two thousand years.

In the next post, I will explain the sciences, observations, and data that, when accumulated, have made the theory of evolution one of the best-established scientific theories of our time, despite the criticisms of some well-meaning people, who usually oppose it for unscientific or pseudoscientific reasons.

The same post in Spanish

Thematic Thread on Evolution: Previous Next

Manuel Alfonseca