FINE LEVEL COMPETITION OF THE FITTEST. “When a diploid individual reproduces sexually, the two alleles at heterozygous loci are necessarily in competition because reproduction by one allele must be at the expense of the other. Such competition is an inescapable component of the organismal level of evolution that was originally advanced by Darwin and later integrated with the field of genetics during the modern synthesis of the early 20th century.”
http://cshperspectives.cshlp.org/content/7/3/a017608.full