Plukket opp en interessant sak fra podcasten Skeptics Guide to the Universe hvor Steven Novella påpekte absurditeten med at sex mellom søskenbarn er forbudt i enkelte amerikanske stater. Bakgrunnen for et slikt forbud er at man mener risikoen for genetiske feil er for høy i slike forhold. Men et slikt lovverk stammer fra en tid før man visste særlig mye om dette, og nyere viten viser at et denne type forbud egentlig ikke kan forsvares. Risikoen for genetiske feil er nemlig svært liten, og ikke høyere enn om man får barn i en alder av 40+ år.
Jeg googlet litt på dette, og Wikipedia bekreftet påstanden:
In April 2002, the Journal of Genetic Counseling released a report authored by a team of scientists led by Robin L. Bennett, a genetic counselor at the University of Washington and the president of the National Society of Genetic Counselors, which showed that the potential risk of birth defects in a child born of first cousins was slightly higher than the risk associated with a non-cousin couple. The report estimated the increased risk for first cousins at 1.7 – 2.8 % over the base risk of about 3%, or about the same as that of any woman over age 40, or of a still younger man (see paternal age). Put differently, first-cousin marriages entail roughly the same increased risk of birth defects as a woman faces when she gives birth at age 41 (roughly 6%) rather than at 30 (roughly 3%). Critics argue that banning first-cousin marriages would make as much sense as trying to ban childbearing by older women. These numbers were reported only for first instances of cousin mating; repeated generations of cousin coupling are thought to increase the risk substantially.
Eller sagt på en annen måte:
Children of non-related couples have a 2-3% risk of birth defects, as opposed to first cousins having a 4-6% risk. […] In plain terms first cousins have at a 94 percent + chance of having healthy children. […] The National Society of Genetic Counselors estimated the increased risk for first cousins is between 1.7 to 2.8 percent, or about the same a any woman over 40 years of age.