So, maybe you've seen the news today about Representative Todd Akin. He's the republican nominee for Senate in Missouri, running this year against Claire McCaskill. In an interview he said that he opposed abortion in all circumstances, with no exception for rape, because rape does not lead to pregnancy, see, because, "If it's a legitimate rape, the female body has ways to try to shut that whole thing down." (Quotes on Jezebel, video here.)
After realizing that he sounded like a complete shithead, even for a contemporary Republican (and probably after receiving a scolding from national Republicans), he issued a statement in which he claims that he "misspoke," which is politician speak for, "I accidentally said what I actually thought, and then discovered that it will negatively impact my election chances, so I'm going to lie now. No backsies!"
Although, to be fair to Akin, nowhere in his statement did he back down from the position that abortion should be outlawed without exception, merely that he would advocate for "justice." Also, jobs!
Setting aside for the moment the woeful state of politics, is it true, or even possible, that the female body could have "ways to try to shut that whole thing down"?
Actually, in a lot of non-human animals, something sort of like that does exist.
In species where polyandry (where females mate with multiple males) is common, there is often competition for reproductive access both before and after copulation, where one male may participate in a larger share of a female's reproduction. In many cases, this is going to be something like sperm competition, where differential reproductive success depends on traits associated with the sperm, and by extension, with the competing males. This is not really what we're talking about, though.
In a few cases, you can actually get "post-copulatory female choice," where it is clearly the female deciding whether or not to allow fertilization. One such set of cases occurs in some spiders and crickets, where the male transfers a spermatophore to the female. This is basically a bag full of sperm that is attached to the female during copulation. She may then modulate the success of the sperm through the amount of time she permits it to remain attached to her.
For example, here's a paper on field crickets that shows not only that females modulate spermatophore retention time in response to male song quality, but that this modulation is contingent on the female's prior experience. This is important because it emphasizes the aspect of female choice.
But what about humans? Well, actually, yes. Human females have the capacity to engage in post-copulatory female choice, such that they do not necessarily have to give birth to their rapist's child. It's called safe, legal abortion. It still exists in this country, but if too many more Todd Akins get elected, the American female body will no longer have "ways to try to shut that whole thing down."
Rebar, D., Zuk, M., & Bailey, N. W. (2011). Mating experience in ﬁeld crickets modiﬁes pre- and postcopulatory female choice in parallel Behavioral Ecology, 22, 303-309