Thought leaders on teamwork assert that diverse teams perform better; findings in the area of complex adaptive systems suggest the same. Recent Twitter discussions and various blogs have raised concern, yet again, over a lack of diversity in IT. For example, the topic of "too few women in software development" always comes up, perhaps because it is painfully obvious at tech conferences, and perhaps less politically sensitive to discuss than some other marginalized groups.
In North America, historically, women have made up 10 to 20 percent of the IT community, and yet some conferences still feature less than 10% women among their presenters. (Female speakers are still entirely absent at some conferences). It's true that there are fewer women than men to choose from in IT, but if this were the only reason we'd expect to see, on average, 10% to 20% of senior speakers being female. It just isn't the case in too many places.
There are certainly many factors at play, including the fact that women are more likely to turn down invitations due to the requirements of family life; and some choose to become less visible in response to harassment. But top notch speakers of any gender are reportedly difficult to find - and those who are most sought after have probably honed their skills by speaking at smaller, proposal-driven conferences before they were ever invited to speak. Reasons cited that women submit fewer conference proposals and speak less frequently include: lack of confidence (see Imposter Syndrome, which is not limited to women) and lack of practice or information on how to write a good proposal.
In response to this issue, Lisa Crispin has suggested that, for example, women speakers help less experienced women to write strong conference proposals, to put a larger number of deserving women in the public eye (a strategy that could also be used to encourage participation by other underrepresented groups). Jim Holmes offers help for those new to writing conference proposals. This is also valuable for those who encouraging them to submit by assisting with the process. Search engines reveal a number of other resources available to help newbies understand how to get involved in conferences, including Kathy Sierra's How to speak at a tech conference.