From: here

How many female players are there in the top levels of chess? In the top hundred the answer is one percent, and that 1% is named Judit Polgar. But how about the top thousand? Using the latest available FIDE rating list for all players we were able to extract exactly 22 female players, which works out to (whip out your calculators, boys and girls) 2.2%.

For a long time we have known that there is a gap in performance between boys and girls in mathematics skills. In a new study, Jonathan Kane, a professor of mathematical and computer science at the University of Wisconsin, Whitewater, and Janet Mertz, a professor of oncology at the University of Wisconsin, Madison, examine this gender gap and test several popular explanations. Their cross-cultural analysis seems to rule out several causal candidates, including coeducational schools, low standards of living, and innate variability among boys.

I am not sure what science is behind the "gap" in boys and girls with concerns to math and chess.  I find both math and chess to be terribly boring and would much rather play a game of poker or read a good book! 

We recently have witnessed how well women can do at chess.

Hou Yifan, 17 year old girl from China and woman´s world champion, has done extremly well at the powerful Tradewise Chess Festival in Gibraltar.

Hou was in the lead going into the last round, but was caught at the last moment by Nigel Short. They both scored 8 points in 10 games and the English grandmaster grabbed the title in a blitz playoff. But Hou faced much tougher opponents. Facing six grandmasters rated above 2700 points - a barrier reserved for the best 40 players in the world - she scored four wins and two draws, including a historic win against Judit Polgar, the all-time best woman.

That´s why there is a gap.

I agree.

I ve always claimed that the best female chess player will always be less than the male player, or the best female mathematician is no match to the male one.

Yes, there is a gap, huge gap.

In Math results on a highschool level boys and girls in the Netherlands a gender gap is not visible. American research has also shown that 40 years ago boys were better than girls in Math, but over time this gap has decreased steadily, making it minimal in recent years. The gendergap in Math skills is visible in some countries, and not in others. This points towards a cultural gap, rather than a gap in actual skills. Math (and chess) is presented as a "boy thing", whereas foreign languages (and perhaps dancing, or baking cupcakes) are presented as a "girl thing."

So, in my opinion the best female chessplayer will not "always" be worst than the best male player. It is a matter of time, and breaking cultural barriers. The number of female candidates winning Math competitions has also been steadily climbing in Europe over recent years, so chess is next!

For the people who like the science behind it, this is a research done in 69 countries, pointing towards, amongst other, school enrollment of girls as a determinant of math skills, and not weither a kid has a hoha or a wiwi http://www.apa.org/pubs/journals/releases/bul-136-1-103.pdf