Here are the first lines of Ken Ham’s blog post, “Why Is Marriage Just for Two?”

For years I have been asking the question “why only two?” to those people who support gay marriage. You see, the idea of marriage being between only two people is biblically based.

Where to even start?

The Bible is a collection of 66 books written by 40 authors over a period of hundreds of years. The Old and New Testament are contradictory on a number of points, such as whether God requires his followers to follow the Levitical Law. Ham and other evangelicals hold that in the New Testament, Jesus “fulfilled” the law, rendering it null and void. This alone, outside of any other contradictions, suggests that it is incredibly overly simplistic to say something is “biblically based.”

When Ham says that the idea of marriage being between only two people is biblically based, I have to wonder what part of the Bible he’s talking about. Yes, in Genesis God creates Adam and Eve, one man and one woman, and speaks of the two becoming one flesh. But in the same book, God chooses as his followers men who almost universally take more than one wife—and the Bible says nothing to suggest these men were operating outside of God’s will in doing so. Jacob takes two wives and two concubines, and yet God treats his twelve sons by these four women as all equally legitimate.

In the Old Testament, God lays down laws for his people. He carefully regulates who men can take as a wife—not a niece or a sister, for instance—but never prohibits polygamy. Instead, it accommodates it, requiring men who take a second wife not to deprive the first wife of food or clothing, for example. Indeed, the entire Old Testament is, to my knowledge, bereft of any suggestion that marriage is only to be between one man and one woman. Instead, polygamy is treated as normal and accepted and, for the wealthy and powerful, even expected.

King David, who is repeatedly described as a man after God’s own heart, took nearly a dozen wives. God severely punished David for taking Bathsheba as his wife, given that she was originally married to another man and David had him killed to obtain her. But God never punished David for taking his other wives.

Polygamy isn’t condemned in the New Testament, either. In Timothy and Titus, church leaders are required to be the “husband of but one wife,” but this is the only time polygamy is referenced in any way. I’ve seen it argued that Jesus is condemning polygamy when he speaks of marriage and says “the two shall become one flesh,” but in that passage he is referencing a Genesis passage that says the same thing—and as we’ve already noted, the Old Testament permits polygamy. The New Testament writers condemn gluttony and prostitution and anger—but not polygamy, despite the fact that polygamy existed in Jewish culture at the time.

And yet Ken Ham thinks marriage being between two people only is biblically based. What’s more, he doesn’t even bother to back up his assertion—he simply assumes it is transparently obvious.

Don’t get me wrong, creationists like Ham try to find ways to explain all of this away. And in some sense that’s fine—I don’t have a problem with people arguing that Christians should be monogamous, or finding ways to interpret the bible to support monogamy. I do, however, have a problem with Christians arguing that something is transparently obviously and unquestioningly biblical when it is anything but. Go ahead and form your own interpretation—but please, oh please, don’t claim the Bible is “clear” on an issue when it’s obviously more complicated than that.

Christianity is monogamous not because of anything the Bible says but rather because the Romans were monogamous. Christianity was profoundly influenced by its development within the Roman Empire. Even the Christian concept of heaven and hell comes from the Romans, not the Jews. While Jewish law permitted polygamy, the Romans were fiercely monogamous, and during its early years Christianity moved from being a Jewish sect to being an independent religion within the Roman Empire—a religion adopted primarily by Gentiles (and not Jews) and ultimately made the Roman Empire’s official religion.

Yes, you read that right—the Western idea that marriage is between one man and one woman isn’t biblical, it’s Roman.