Science magazine has asked stem cell pioneer Hwang Woo-suk to explain the controversy over how he obtained human eggs for his research.

A spokesman for the American Academy of Arts and Sciences on Tuesday said no evidence exists that the controversy impugns Hwang's accomplishments thus far.

In a statement released Monday, Science editor Donald Kennedy said his team is looking into Hwang's thesis on stem cells submitted last year, adding the magazine takes the controversy very seriously.