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DETROIT, MI - MAY 4:  Republican Dr. Ben Carson, a retired pediatric neurosurgeon, speaks as he officially announces his candidacy for President of the United States at the Music Hall Center for the Performing Arts May 4, 2015 in Detroit, Michigan. Carson was scheduled to travel today to Iowa, but changed his plans when his mother became critically ill. He now will be traveling to Dallas instead to be with his mother Sonya. (Photo by Bill Pugliano/Getty Images)
DETROIT, MI - MAY 4:  Republican Dr. Ben Carson, a retired pediatric neurosurgeon, speaks as he officially announces his candidacy for President of the United States at the Music Hall Center for the Performing Arts May 4, 2015 in Detroit, Michigan. Carson was scheduled to travel today to Iowa, but changed his plans when his mother became critically ill. He now will be traveling to Dallas instead to be with his mother Sonya. (Photo by Bill Pugliano/Getty Images)

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A look back at Ben Carson on fetal tissue research

Former neurosurgeon and current Republican Presidential Candidate Ben Carson's past comments came to attention after news of his research using aborted fetal tissue broke.

A look back at Ben Carson on fetal tissue research

Former neurosurgeon and current Republican Presidential Candidate Ben Carson's past comments came to attention after news of his research using aborted fetal tissue broke.