Not long after the revelation that Republican presidential candidate and retired neurosurgeon Ben Carson participated in a study that used fetal tissue – despite his claims that such research is never necessary – Carson sought to distance himself from the work. 

“Today I was accused by the press as having done research on fetal tissue. It simply is not true,” Carson said in a Facebook post late Thursday. “… I, nor any of the doctors involved with this study, had anything to do with abortion or what Planned Parenthood has been doing. Research hospitals across the country have microscope slides of all kinds of tissue to compare and contrast. The fetal tissue that was viewed in this study by others was not collected for this study.”

The study’s methods section says the slides were obtained from “two fetuses aborted in the ninth and 17th week of gestation.”

Carson, as well as the rest of the Republican field, has condemned Planned Parenthood doctors discussing the donation of fetal tissue in secretly recorded videos, and some Republicans have condemned the entire practice. Carson previously called the videos evidence of “how far we have drifted in terms of our humanity.” Last week, Carson told msnbc, “It should be made very clear to people that the types of things we’re discovering by using fetal tissue can also be discovered by using non-fetal tissue. So it’s not like it is the only source as they try to make it sound.”

On Fox News’ The O’Reilly Factor Thursday night, Carson called the reports “propaganda.” But he also said, “Just because they get the fetal tissue doesn’t mean they should throw it out. Of course they don’t. That’s how science is advanced.”

Another Republican candidate who is trailing Carson in the polls, former Pennsylvania Sen. Rick Santorum, told CNN Friday that he would not have conducted research involving fetal tissue. (As a congressman, Santorum voted against lifting the ban on fetal tissue research.) “It’s used to, I won’t say coerce, certainly make women more comfortable about having an abortion,” Santorum said.

The secretly recorded tapes make clear that the consent process to the donation of fetal tissue – which takes place in less than five states and only for the small number of later abortions – happens after the consent to the procedure. “I think that a lot of people feel strongly that the conversation shouldn’t be had until after they’ve made their decision to terminate, they know how far along they are and they know what’s going to happen, and when all that is said and done, and they’ve had time for all of that to sink in, then it’s time to basically say, this is how we normally handle the tissue, but if you would be interested, here’s another opportunity to contribute to research, contribute to science, donate your tissue,” Deborah Nucatola, a Planned Parenthood executive, says in the first video released. 

Meanwhile, Carson faces other potential problems with the anti-abortion wing of the Republican Party. When asked Thursday on a different Fox News show about rape exceptions in a theoretical abortion ban, Carson said of rape survivors, “I would hope that they would very quickly avail themselves of the emergency room, and in the emergency room, they have the ability to administer RU-486 and other possibilities before you have a developing fetus.”

RU-486 is a chemical abortion pill administered by doctors to end a pregnancy, fiercely opposed by anti-abortion activists like any other abortion procedure. Carson may or may not have been referring to an entirely different drug, emergency contraception, which is a high dose of birth control that does not end a pregnancy but prevents fertilization. Many anti-abortion activists also oppose emergency contraception, either out of opposition to any birth control, or because they believe that it may interfere with the implantation of a fertilized egg, something it has never been shown to do.  

Carson also said he believes life begins “certainly once the heart starts beating, certainly at that point.”