Making Sense of the Neutral Theory

Neutral Theory noted that at the molecular level, evolutionary changes that occured are selectively neutral and is driven by genetic drift rather than by natural selection. (you already know this)

Because of selective neutrality in mutations (no effect on fitness), polymorphism is found within a population and all of its individuals can reproduce to pass on their different alleles. With that, the only determinant for the propagation of a particular allele will be genetic drift - chances that a particular allele will be passed on, which increases in a smaller population.



The theory sets the basis for the Molecular Clock:
Kimura, King and Jukes made the assumption that most aa substitution

- occur at a constant rate and
- are selectively neutral
(=the substitution is not lethal and does not affect the fitness of the organism)

Since the fitness of organism is not affected despite the mutation, we can thus track the changes in aa sequences over a long period and we can also observe polymorphism within a population.

And since the substition occurs at a constant rate, by observing the aa sequences diferences of particular proteins or genes for two species, we can deduce their evolutionary history i.e their approximate period of divergence from a common ancestor.

If a particular gene is important in function, variation in the resultant aa sequences will not be observed frequently