Science has made us understand the importance of cross-breeding. Even among the human race, cross-breeding is very important. It gives us stronger bodies and helps in reducing the effect of some genetic sickness. We should appreciate the benefits of scientific knowledge. We should appreciate what God has helped humanity to achieve scientifically.
The Bible does not say we should marry our closed relatives. We have seen that Abraham took his wife from among his sisters. That was what he told Abimelech. He told him that Sarah was his sister. Rebecca was a cousin to Isaac. These were the trend possibly from the very beginning of creation.
But God altered that trend when he told the Israelites through the law which he gave them, that they should not uncover the nakedness of their relatives. This is enough to suggest to us that God is against marrying a closed relative. So, the Bible does not support marrying a closed relative.
