Is Neutrality Problematic For Evolvability
Kimura (1983) is one of the key players of research into genetic neutrality and had a major role in its rise to prominence. Kimura referred to neutrality as genetic variation that does not result in change to the fitness of an organism. Moreover any change has to remain neutral in any environmental, genetic or physical condition.
Wagner (2005) claimed that this definition of neutrality actually caused the biggest problem to neutrality. Firstly how can one test, set limits and measure fitness. Wagner (2005) used bacterial strains grown under laboratory conditions to exemplify this predicament. One can assume that the growth rate of these bacterial strains can be used to show the various fitness levels between different strains. But there are numerous possible conditions that the strains can be put under, such as fitness at varying temperatures, starvation conditions. And other factors can be used to measure fitness like germination rates and their sporulation efficiency. The question is which one of these is the correct method to determine fitness and has the most relevance, something which many evolutionary biologists consider an almost impossible question to answer. This is something which is amplified which is amplified with much higher species such as human, where a whole host of other factors come into play like, fertility, reproductive capacity and mortality amongst numerous others.
Neutrality assesses resistance to particular mutations but here stems another problem. Many enzymes and proteins are multifunctional, and for some, not all functions have been revealed. P53 is a good example of a protein which exhibits multiple functions. It can hold a cell in the G1/S checkpoint of the cell cycle, it can initiate DNA repair and can send a cell into apoptosis (Jin, 2001). These are just some of the functions we are aware of. Because of the ambiguity we cannot judge the neutrality of mutations in genes accurately until all functions are known.
