A couple of years ago driving through the south of France I stumbled across this sign, and even if your French wasn't up to the job, the cartoon mascot was easy to read.
This week a Sausagefest of a different sort has been bouncing round the science tweetosphere: a big, international quantum chemistry conference with 29 plenary speakers and session chairs, all of whom were men. And yes, the physical and mathematical sciences are far from a 50/50 gender ratio, so you would be rightly surprised if the list was 50% female. But the odds of having no women at all in a field that is 10% female are about 1 in 20. And if quantum chemistry is 15% female, the odds of an all-male line-up drop to less than 1 in 100. [I'll leave the proof as a homework exercise.]
Today, I was looking at a conference announcement in my own field and it was the same deal, roughly 30 names (between the organising committee and invited speakers) and all men, to the best of my knowledge. Gender ratios vary significantly between adjacent subfields, but there are plenty of smart, high-profile and enormously talented women in astrophysics and cosmology -- which puts this outcome in the 1% category.
If you want reasons other than random chance for an all-male list of speakers there is no shortage of options. There is even a helpful bingo card.
But the most likely reason is this: the (100% male) organisers asked the obvious, easy people, and those people just happened to be male. No-one decided not to invite any women, but a series of disconnected decisions led to just that result -- an emergent phenomenon, if you want.
I have organised conferences and run colloquia and seminars. And I love it. You get to invite smart people doing interesting work to visit, you hear what they have to say, and then you take them out to a decent dinner. As "service" tasks go, it beats being on the committee that sets the Qualifying Exam for the PhD students.
Now, here's the funny thing: if you draw up a list of speakers you always check it for variety against a slew of different criteria. Did I accidentally fill the departmental colloquium with cosmologists this semester, and will my colleagues complain? Have I invited three people from Princeton to visit in the same month? Do the 26 speakers for my conference cover all the hot topics in the field? Did I remember to invite anyone from Europe?
So checking for gender equity on a list of conference speakers isn't difficult -- you are already looking for half a dozen different kinds of balance, and this is just one more. It's really not that hard to get right, and it matters.