4 Reasons Why Cain Could Marry His Sister

1. Only close relatives were available.

The Bible shows us that everyone descends from the first two people, Adam and Eve. We didn’t evolve from a shared ancestor with monkeys and apes. We were created in the image of God about 6,000 years ago. God made Adam from dust and Eve from Adam’s side. Adam called his wife Eve because she would be the mother of all people. Cain didn’t have a secret source for a spouse. He had to marry a descendant of Adam and Eve. Since these two people were his parents, the only other possible women alive on earth for him to marry must have been descendants of his parents—his sister or maybe a niece.

2. Marriage between close relatives wasn’t prohibited.

Yes, the Bible does prohibit marriage between brothers and sisters. Look no further than the Mosaic Law. But the Mosaic Law was given about 2,500 years after Cain. It was permissible before the Law.

3. Marriage between close relatives wasn’t scientifically and medically dangerous.

Today, if a brother and sister marry, there is a high probability that their children will have severe medical disabilities. In our day, which is around 160 generations since Cain, the human population carries a load of DNA mistakes—mutations. However, people who are not close relatives tend to have different mutations. If these people marry, any mutations that one spouse passes on will likely be compensated for by a good version of those genes from the other spouse. Children of close relatives have a higher probability of inheriting two mutated versions, leading to disabilities—if the child survives at all.

In Cain’s day, just a single generation removed from Adam and Eve’s perfectly created DNA, the mutational load would have been much lighter than it is today. He and his sister could have successfully produced healthy offspring.

4. Everyone marries a relative.

For many people, the biblical answer makes their skin crawl. But do you know the genealogical closeness between your parents? Or between you and your spouse? Or you and your future spouse?

Based on the history of human population growth, you and I have a 95% chance of having a shared ancestor just 600 years ago. The explanation is technical, but it’s true for every person around the globe—including for your parents, for your spouse (if you’re married), or for your future spouse (if you’re not married). Put another way, you and I are probably twentieth or twenty-fifth cousins. Or closer. So are your parents. Cain may have married his sister, but everyone is still marrying relatives.