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.

Different types of chance

Jacques Monod

When we don’t know why something happens, we usually say that it is due to chance. But this statement is ambiguous, because there are two different types of chance:

• Epistemological chance, where the cause of what’s happening is well-known, but so complex that it remains outside the scope of our knowledge. Almost all games of chance (dice, roulette, lottery jackpot) are examples of this type of chance. Rolling dice conforms to the laws of mechanics, but the conditions are so complex that we cannot predict the result of each roll. This type of chance is what Jacques Monod called operational uncertainty in his book Chance and Necessity (1970):

This term is used... in relation to the game of dice, or roulette, and the calculation of probabilities is used to predict the result of a play. But these purely mechanical and macroscopic games are not "the result of chance" except because of the practical impossibility of controlling the throwing of the dice or the ball with sufficient precision. It is evident that a very high precision launching mechanism is conceivable, and would make it possible to largely eliminate the uncertainty of the result... The same thing happens, as will be easily seen, in... many phenomena where the notion of chance and the calculation of probabilities are applied for purely methodological reasons. (My translation into English).

Darwin’s mistake

Charles Darwin

Consider the following paragraph by Darwin in The descent of man (chapter 5):

With savages, the weak in body or mind are soon eliminated; and those that survive commonly exhibit a vigorous state of health. We civilised men, on the other hand, do our utmost to check the process of elimination; we build asylums for the imbecile, the maimed, and the sick; we institute poor-laws; and our medical men exert their utmost skill to save the life of every one to the last moment. There is reason to believe that vaccination has preserved thousands, who from a weak constitution would formerly have succumbed to small-pox. Thus the weak members of civilised societies propagate their kind. No one who has attended to the breeding of domestic animals will doubt that this must be highly injurious to the race of man.

It seems incredible that, after a lifetime devoted almost exclusively to meditate on his theory of evolution, Darwin made the mistake of applying it wrongly to humans, as is clearly demonstrated in the paragraph I have just quoted.

Natural selection is more complicated than we thought

Jacques Monod

In his famous popular book Le hasard et la nécessité (1970), Jacques Monod said that evolution is the result of the interaction of two types of phenomena: chance (mutations, environmental changes) and necessity (natural selection) .

More precisely, natural selection can be considered as the action of a random element (the environment) over another random element (the genetic make-up of living beings). According to the synthetic theory of evolution, who is now over 80 years old, that action is quasi-deterministic (Monod’s nécessité).

A further development of the synthetic theory of evolution is Richard Dawkins’s selfish gene theory, which asserts that adult living beings are just the means that allow genes to perpetuate. Although it had some significant detractors (Stephen Jay Gould, for instance), this theory was accepted by many biologists in the two decades after its statement.

However, in recent years, advances in genomics and evolutionary biology are beginning to question the accuracy of the synthetic theory of evolution and the selfish gene. Make no mistake: this does not mean that the theory of evolution is in question, what is being discovered is the fact that things are not as simple as they seemed. The following is a sample of some of the problems detected, culled from the book The year in evolutionary biology, Annals of the New York Academy of Sciences (2008).

·         Epigenesis: genes are more interconnected than thought. A mutation in a gene can make another gene work in a completely different manner, complicating the action of natural selection.

·         Quasi-neutrality: slightly deleterious mutations seem to be immune to natural selection and are perpetuated over generations.

·       

The tree of life

  The development and hybridization of viviparous beings (which include such different organisms as mammals and flowering plants, among others) are not as simple as implied by the Dobzhansky-Muller principle, associated with the synthetic theory of evolution. Hitherto unsuspected effects take a part, such as genomic imprinting (substantial differences in the expression of maternal and paternal genes during development).

·         The fundamental dogma of the synthetic theory (the genotype uniquely determines the phenotype) is now questionable. Not only it is true (what was already known) that the genotype is plastic, and depending on the environment can lead to several different phenotypes (to see this, just compare the different types of cells of the same organism, which are very different, although they share the same genome). What is unexpected is the finding that several different genotypes may result in the same phenotype; a setback for Dawkins’s selfish gene theory. The relationship between genotype (genes) and phenotype (the physical aspect of the living adults) happens to be many-to-many in both directions, and the development of the phenotype from the genotype is more deeply influenced by the environment than previously thought.

The same post in Spanish
Thematic thread on Evolution: Preceding Next

Manuel Alfonseca