Autism is a neurological disorder thought to be caused by mutant alleles of one or more genes. Scientists had been wondering why the number of children diagnosed as autistic increased dramatically in a decade, from 1 in 500 in 2002 to 1 in 88 in 2012. Researchers now think that they might have found at least part of the answer: Men are fathering children at later and later ages. A paper published in the journal Nature in 2012 showed a correlation between paternal age and the incidence of autism; the age of the mother was not a factor. How does this observation provide a possible explanation for the apparent increase in the rate of autism?

The germinative cells that will become sperms are under constant mitosis. During this process, DNA mutations can happen and be transmitted from one generation of cells to the other as the years go by, and more cell divisions take place, more mutations the DNA in the sperm will have. When the number of mutations reaches a certain level, his child will express these mutations and have autism.

The egg of the mother is not a factor because the germinative cells in women are not under constant mitosis, so there is not an accumulation of gene mutations. Women are born with an exact number of eggs for all their life.