Here’s a puzzle. If evolution ensures that ‘good’ genes spread through a population, then why are individuals so different? Why don’t people get better and better looking through each generation to the detriment of ugliness and lead to a population of real lookers?
The problem with current evolutionary theory is that it would seem that if females select the most attractive mates, then the genes responsible for their attractive features would spread quickly, leading to all males becoming equally attractive (think peacock tails). Ultimately, further sexual selection would then no longer take place and evolution would stop in its tracks.
This is the so-called lek paradox and it has remained a foil in the weaponry of the intelligent design advocate’s arsenal for many years. Until now.
Thanks to research at Newcastle University, England, this apparent fundamental flaw in Darwin’s theory of evolution, latched on to by creationists can be explained quite effectively by evolution itself. The findings of Newcastle’s Marion Petrie and Gilbert Roberts research suggests that sexual selection leads to increased genetic diversity by a mechanism not previously understood.
Petrie reasoned that as genetic mutations occur naturally anywhere in the genome, some will actually affect those used to produce the DNA repair kit enzymes found in all cells. This would lead to those individuals with a malfunctioning or inefficient repair kit, having more mutations left unrepaired and so greater variation in their genome.
Usually, damaged DNA leads to an unviable organism that either dies quickly of the effects or is otherwise unable to reproduce. However, if those variations are present in sections of the genome responsible for disease defence, then variation can actually be beneficial as greater variation in the genome at these points means more chance of warding of bacteria and viruses.
Petrie modelled the spread of genes in a population and demonstrated that the tendency towards reduction in genetic diversity caused by sexual selection is outweighed by the maintenance in greater genetic diversity generated by mutations affecting genome repair.
The researchers began this research a decade ago and their model genes are now a great fit for the observations of variations. “We find that sexual selection can promote genetic diversity despite expectations to the contrary,” Petrie says. The team publishes details of their findings today in the journal Heredity.