During the course of my PhD research for the book that became The Battle of the Sexes in Science Fiction I had to learn a lot about ye olden day beliefs about sex and sexuality, including conception. For instance I came across this in Thomas Laqueur’s book Making Sex:

Samuel Farr, in the first legal-medicine text to be written in English (1785), argued that “without an excitation of lust, or enjoyment in the venereal act, no conception can probably take place.” Whatever a woman might claim to have felt or whatever resistance she might have put up, conception in itself betrayed desire or at least a sufficient measure of acquiescence for her to enjoy the venereal act. This is a very old argument. Soranus had said in second-century Rome that “if some women who were forced to have intercourse conceived . . . the emotion of sexual appetite existed in them too, but was obscured by mental resolve,” and no one before the second half of the eighteenth century or early nineteenth century question the physiological basis of this judgement. The 1756 edition of Burn’s Justice of the Peace, the standard guide for English magistrates, cites authorities back to the Institutes of Justinian to the effect that “a woman can not conceive unless she doth consent.” It does, however, go on to point out that as matter of law, if not of biology, this doctrine is dubious. Another writer argued that pregnancy ought to be taken as proof of acquiescence since the fear, terror, and aversion that accompany a true rape would prevent an orgasm from occurring and thus make conception unlikely.

Thus the statement of Todd Akin, the Republican nominee for the Senate in Missouri, that

from what I understand from doctors [pregnancy from rape] is really rare. If it’s a legitimate rape, the female body has ways to try to shut that whole thing down

does not come out of nowhere. It comes out of long debunked pseudo-science dating back centuries to a time when it was also believed that women could give birth to rabbits.