Acoording to a research done by Yaniv Erlich a scientist at ColumbiaUniversity and the Chief science of officer of the DNA test company MyHeritage have looked into determining at what point in history marrying your cousin was frown upon and the chance of a baby being born with birth defects due to consanguinity. In today society marriage between cousin is oddly viewed but in earlier times, cousins used to get hitched all the time. Such as Franklin Delano Roosevelts who married his fifth cousin Elenor or Albert Einstein and Charels Darwin who married their cousins too. From the 1650 to 1850 and individual on average was on average, fourth cousins with their spouse. By 1950 married couples were on average seventh cousins, according to Erlich. There was more of an expansion between cousins marrying each other in a within a centuary beacuse before1950 most people married someone who lived within a six mile radius of where they were born. Of course other factors played a role in marriages between cousins which influenced families to marry between each other such as money, power and control of territory.
Now modern time many states moved to outlaw cousin marriage. Today 24 states ban marriage between first cousins, while 20 states allow it. The others allow first cousins to couple up, but only under certain circumstances which include only both are over 50 or 55 or 65. Depending on the state the marriage is allowed if one or both are permanently infertile and only if the couple has received genetic counseling. First cousin share 12.5 percent of their DNA while parents and kids share about 50 percernt. Therefore any child that results from first cosuin union will have a similar looking genes which can result in future problems. Its estimated that 4 to 7 percent of children born to first cousins are likely to have birth defects, compared o 3 to 4 percent for children whose parents are more distanltly related. The real issue would rise if the next generation of kids also married their first cousins because their offspring would have even more DNA in in common and an even greater chance for birth defects. Odds of healthy offspring improve with each distance of relation. Second cosuins share 6.25 percent og their genes and third cousins share just over 3 percent. Any further cousins for the most part have no meaningful genetic relation at all.
https://www.popsci.com/marrying-cousins-genetics
https://www.theguardian.com/science/2013/jul/04/marriage-first-cousins-birth-defects
