The president of Harvard University has caused a stir among academics by suggesting women have less innate ability at science and maths than men.
Dr Summers called for more research into gender differences
Former US Treasury Secretary Lawrence Summers argued one group outperformed the other because of genetics, not just experience, the Boston Globe said.
Several guests walked out of a conference after hearing the comments.
Dr Summers said later that the shortage of senior female academics was partly because of child-minding duties.
These would make it difficult to work the 80-hour week needed for advancement.
Dr Summers said the theory that men were more naturally able at sciences was based on research, not his own opinions.
Boys had achieved more top scores in tests than girls and the difference needed further investigation.
Richard Freeman, the organiser of the conference, held at the National Bureau of Economic Research, in Cambridge, Massachusetts, said Dr Summers had been asked to be provocative.
Dr Freeman told the Globe: "I predict he will get more things done on women and faculty issues because he's a straight-talking, no-baloney president."
Nancy Hopkins, of Massachusetts Institute of Technology, was one of the academics who walked out of the conference.
She said that, had she not done so, she "would have either blacked out or thrown up".
However, Dr Summers said in a statement: "My remarks have been misconstrued as suggesting that women lack the ability to succeed at the highest levels of math and science. I did not say that, nor do I believe it.
"I am deeply committed to the advancement of women in science, and all of us have a crucial stake in accelerating progress toward that end."
He added that the "harder we work to research and understand the situation, the better the prospects for long-term success".
Dr Summers has been president of Harvard since 2001, having previously served for several years in President Clinton's administration.