From Science:
Cutthroat competition in the testes might explain the unexpected prevalence of a mutation that halts skull growth and fuses fingers and toes. The genetic glitch seems to give some sperm precursors an advantage by speeding their division, a new study suggests.
Apert syndrome afflicts one in every 70,000 children who are born with fused bones in their heads, hands, and feet. That incidence, although low, is 100 to 1000 times higher than the average mutation rate. The fault occurs at one spot on a single gene on chromosome 10 and is linked to the father’s age. Researchers first theorized that the site might be susceptible to genetic errors, a mutation “hotspot.” More recent studies posited that the mutation might instead confer some advantage to germline cells–sperm progenitors–in natural selection.
Computational biologist Peter Calabrese of the University of Southern California (USC) in Los Angeles developed mathematical simulations of how the mutations might arise and develop in each scenario.
More here.