Reuters reports on a research study by Dr. Neri Laufer (Hadassah University Hospital, Jerusalem) into the genetic variation underlying fertility in older women. The newsworthy finding is the identification of a "select group of genes" that influence late fertility:
Using gene chip technology, [Laufer] and his team compared the genetic profiles of eight women chosen from 250 who had had children past the age of 45 with profiles of six others who had finished their families by the age of 30.
"These women appear to differ from the normal population due to a unique genetic predisposition that protects them from the DNA damage and cellular aging that helps age the ovary," he said.
Conceiving naturally past the age of 45 is rare because a womans supply of eggs diminishes as she ages and approaches the menopause, which normally occurs around the age of 50.
The report implies that the alleles may be more common in some groups than others. Although it does not say, the geographic extent of the samples was almost certainly limited, so the following cannot be considered conclusive, but it is interesting:
All the super-fertile women in the study were Ashkenazi Jews, descended from the Jewish communities of central and eastern Europe. Most had had six or more children, did not use contraception and had a low miscarriage rate.
"They challenged their reproductive system until the menopause," said Laufer, who added that the distinct genetic fingerprint was not unique to them.
He found a similar profile in Bedouin women who also had children late in life.
It might be highly localized, it might be global. Whichever is the case, this is certainly interesting from the standpoint of the evolution of life history traits in humans. The persistence of fertility into later adulthood would seem to be highly adaptive, unless the allele has some cost for earlier survival or reproduction. The distribution of the allele and that of linked loci could tell us if it has been recently spreading, or if it is an ancient polymorphism. To my knowledge, this is the first examination of the determinants of fertility late in life, as opposed to genetic determinants of mortality. The shape of human life histories is affected by selection on both, so this is an important step.