Whether one truly believes in the Bible or not, it seems to have become a social standard to attribute one's own assumptions of right from wrong on scripture.
Unfortunately, many times the person who claims that something is "a sin against God," or that an individual will "burn in Hell" for his actions or lifestyle have no clear understanding of what Scripture says on the subject.
Perhaps even more unfortunate is that many preachers, priests, and theologians have also allowed society to cloud their judgment on the issue, rather than to study what the Bible has to say on the subject for themselves.
I know you asked about first cousins, but all the research I’ve found uses second cousins as the benchmark of consanguinity (more commonly known as intermarriage).These people note that 20 percent of marriages around the world are between first cousins, that Albert Einstein and Charles Darwin married their first cousins, and that first-cousin marriage, while prohibited in half the United States, is legal in Canada and throughout Europe.Now a study by the National Society of Genetic Counselors says that having a child with your first cousin raises the risk of a significant birth defect from about 3-to-4 percent to about 4-to-7 percent.In this discussion, we will consider only the biblical history and acceptance of cousin relationships, as opposed to institutional creeds.(For a complete discussion on the Catholic Church, please see our Chat with an Expert page.) For much of the world's population, the Bible is the final authority on right and wrong.