Thursday, February 26, 2015

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.

Manuel Alfonseca

No comments:

Post a Comment