CBS Local — With online genealogy companies growing in popularity, a new study is suggesting that marrying a cousin should not be considered a bad thing for your family tree.
Data scientists at Columbia University have published a report in the journal Science that examines the DNA of a 13 million member family tree and data found in online genealogy profiles. The research found that first cousins share about 12.5 percent of the same DNA. Second cousins share just over six percent of their DNA while third cousins share about three percent.
According to Popular Science, the modern stigma around marrying cousins boils down to the need for genetic diversity. The more diverse the genes passed down from your mother and father are, the better the odds are that a child will be born without any defects. Simply put, if a father’s DNA does not have the proper resistance to a certain disease then it’s better if the mother has significantly different genes because she may have the proper anti-bodies.
While a diverse gene pool is best for preventing major birth defects, the study found that a marriage between first cousins would only create a four to seven percent chance of birth defects. Unrelated parents had a three to four percent chance of having a child with a genetic defect.
According to Columbia’s Yaniv Erlich, who is also chief science officer of the DNA test company MyHeritage, cousin marriage was common even into the 1950s. From 1650 to 1850 humans were typically marrying their fourth cousins. The study believes that present day humans are likely all 10th to 12th cousins.
In the United States, 24 states ban first cousin marriage while 20 allow the practice. The other six states, including Arizona, Illinois, and Minnesota, have various restrictions on cousin marriage.