Rep. Todd Akin, Missouri’s Republican Senate nominee, caused a public outcry Sunday when he told a local television station that “legitimate rape” rarely leads to pregnancy.

“First of all, from what I understand from doctors [pregnancy from rape] is really rare,” Akin, the Republican Senate nominee in Missouri, said. ”If it’s a legitimate rape, the female body has ways to try to shut that whole thing down.”

Akin later issued an apology, saying he “misspoke” when he made an “off-the-cuff” remark. Empirical evidence suggests that he is indeed wrong: Research published in the Journal of American Obstetrics and Gynecology suggests over 30,000 pregnancies result from rape annually. “Rape-related pregnancy occurs with significant frequency,” the trio of researchers from the University of South Carolina concluded. “It is a cause of many unwanted pregnancies.”

A separate 2001 study – which used a sample of 405 rape victims between ages 12 and 45 – found that 6.4 percent became pregnant.

But while Akin is wrong in his assertion about rape and pregnancy, he certainly isn’t alone. His remarks tapped into a strain of thinking that dates back to at least the 1980s, with anti-abortion politicians from Pennsylvania to Arkansas making the case that the trauma of rape can often prevent pregnancy. The argument does not come up frequently, but when it does, it nearly always leads to political controversy.