Hat tip to the evil growth marketing technique (source long lost, sorry) suggesting use of a default female "outline" avatar to strongly motivate account creation / gender reassignment (and perhaps even replacement with genuine profile pictures)!
I think it's interesting how much thought goes into default avatars, and that it can be used as a marketing tactic. Thanks for providing link to Twitter as well. Guess I'll have to think more about it in the future.
For a service where the early adopters are predominantly male (perhaps an invalid assumption, but a lazy tech stereotype), you have the default picture be the outline of a female to incentivise the male to "correct" the default by uploading their own picture (demonstrating they're a male, rather than female).
Interesting thought process if my interpretation is correct.
The OP was referring to an "evil growth marketing tactic" - it wouldn't be as evil if it were mainly for empathy with the user base rather than as a dark pattern.
Absolutely, I've played around with this. There are tons of open source libraries to determine gender from name. Obviously it cannot be 100% correct, but it can provide a guess
Edit: Twitter recently discussed changing default avatars, in part because their default was often left in place as "fun and cute": https://blog.twitter.com/official/en_us/topics/product/2017/...
My main point was that default avatars can drive sign-ups motivated primarily just to change it.