Theodoret of Cyrus on Cain's wife

I used to roll my eyes every time creationists made a big deal out of where Cain got his wife. I considered the attention they gave it disproportionate to the actual importance of the issue. I figured only ignoramuses and scoffers ever raised such a trivial challenge. Lately, though, I've noticed Cain's wife being raised by ostensibly good scholars as a real problem for a straightforward interpretation of Genesis. I'm a little flabbergasted that anyone would still cling to such a silly objection, but there it is.

Meanwhile, we've been working hard this semester to add historical Genesis commentaries to the CORE library, and we just received a copy of Theodoret of Cyrus's The Questions on the Octateuch Volume I: On Genesis and Exodus. Theodoret was a fifth century bishop of Cyrus, about 100 miles from Antioch. He's not always concerned with the same textual issues that modern creationists are, but very often he addresses very similar themes. Here's what he says on Cain's wife:
Whom did Cain marry?
His sister, of course. At the time, this was not an offense, no law forbidding it, especially since there was no other way to provide for the increase of the race. ... [God] formed one man from the earth, created one woman from him, and filled the whole world with their offspring. To achieve this goal, he allowed intercourse of brother and sister in the beginning, but when the races had increased, he made this kind of marriage unlawful.
Seems obvious to me.

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