It has been shown that kinship determines fertility in humans as well as other mammals, birds, fish and insects. Evidence indicates that once kinship among a couple and their ancestors is taken into account there is no other important factor influencing fertility in a given species. At smaller populations the curve of fertility against kinship rises steeply as kinship rises until inbreeding is reached. At kinship less than an equilibrium point, fertility slowly falls with varying population time courses including: damped oscillation with rapid rise and slow fall seen in the wild, in the lab and by computer model; a two peaked pattern showing slow rise and rapid fall seen in humans, the wild and in computer model; and a single peak showing rapid rise and slow fall in humans, the wild, the lab and computer model, each pattern caused by a post zygotic mechanism or combined pre and post zygotic. Earlier we demonstrated damped oscillation in a population of captive fruit flies.
We hypothesized that the mechanism must be epigenetic and tried giving varying doses of folic acid to our flies looking for an effect.
We were able to demonstrate the two peaked pattern with slow rise and rapid fall characteristic of combined mechanisms.
We were surprised to discover that fertility depression can occur at roughly a dose of folic acid recommended for women. The number of possible confounding factors means that this may coincidental, but considering the importance of the issue this needs more study.