I've never met you and I believe your intentions are good. In a perfect world more female speakers of equal quality to male speakers would be a better, but there may be more research to be done before assuming the organizers had any chance at all of bringing in female speakers for the presentation series (one which I was no part in, and have no interest in).

Saying there are 20% females in a particular industry does not mean that 20% of females are qualified to speak.

It also doesn't mean 20% of females want to speak.

Now, both of those statements are somewhat inflammatory since logically men and women are equal, so how could a greater percentage of men be at the top of an industry, or a greater percentage want to speak?

Professor Roy Baumeister wrote this amazing paper on the subject (which was posted to HN about a year ago).

"Is There Anything Good About Men?" http://www.psy.fsu.edu/~baumeistertice/goodaboutmen.htm

I promise it is worth the entire read, not to be used as weak evidence in a tough conversation.

After considering the full article, and the fact that the twitter development ecosystem is a fairly small industry it is entirely possible that there are far less female speakers worth bringing to speak or that the female speakers who would be great candidates for speaking simply have no interest in doing so. At the same time, even I have a hard time believing that there is not one qualified female speaker interested.

So, what really needs to be addressed is not whether the team had a bias, but whether there was an efficient way to recruit those female speakers. If Aral or anyone else can provide suggestions on systems to achieve that, perhaps a guide of steps, that would be far more beneficial to the community.

[EDIT] Removed "beating up on the people who organized that" and replaced with "assuming the organizers had any chance at all of bringing in female speakers for the"

I recognize that even the edited statement I added has the partial effect of absolving the organizers. My intention is not to absolve them or say it was impossible to find female speakers. My intention was to simply to cast doubt on the assertion that a lack of female speakers was preventable.

[Added] I upvoted the original article because it did call out the presenters, but simply calling them out without providing a novel or proven approach to adding better speakers is simply not helpful. Especially given the complexity in finding great speakers.

To respond to the point made below that efficency is not important, I can't disagree more. Efficiency is always a consideration with anything, anyone does. If there was only one women expert who did not have any public speaking ability, would it be worth spending months training them to speak prior to them speaking so you could fill your 5th spot? I don't think anyone would argue that that makes sense. Obviously it is the extreme, but I, nor the OP, nor anyone else truley knows how hard it would be to get a female speaker for that event without putting on the event yourself.

Time spent getting speakers is time that cannot be spent on other facets.