I didn't know this

"I'd always thought marrying a blood relative as close as a cousin was immoral, and certainly risky if you plan to have kids. Conventional wisdom says only primitive people who live in isolated places marry cousins. It leads to stupid children. But that's a myth.
It's the sort of myth that leads to stupid laws. Half the states in America have banned cousin marriage, but there's no good reason for it. You can marry your cousin and have perfectly intelligent kids.
Take Albert Einstein -- was he intelligent enough for you? His parents were cousins, and he married his cousin. So did Charles Darwin and Queen Victoria. Worldwide, 20 percent of all married couples are cousins. "
From an essay by John Stossel.
Read the entire article here.