Those drastic changes rarely happen, though. In humans, the most recent very well known one was adult lactose tolerance - something that switched lactase off in adulthood no longer does.
edit: and somewhat back to the original point with regards to eugenics - humans have been evolving intelligence for a while already, so selection for intelligence doesn't seem like a dramatic change.
adult lactose tolerance
That, by the way, is an interesting example of both adding functionality (now adults can drink milk!) and losing functionality (the gene which turns off lactase production in adulthood got broken and no longer works in many people).
A long blog post explains why the author, a feminist, is not comfortable with the rationalist community despite thinking it is "super cool and interesting". It's directed specifically at Yvain, but it's probably general enough to be of some interest here.
http://apophemi.wordpress.com/2014/01/04/why-im-not-on-the-rationalist-masterlist/
I'm not sure if I can summarize this fairly but the main thrust seems to be that we are overly willing to entertain offensive/taboo/hurtful ideas and this drives off many types of people. Here's a quote:
The author perceives a link between LW type open discourse and danger to minority groups. I'm not sure whether that's true or not. Take race. Many LWers are willing to entertain ideas about the existence and possible importance of average group differences in psychological traits. So, maybe LWers are racists. But they're racists who continually obsess over optimizing their philanthropic contributions to African charities. So, maybe not racists in a dangerous way?
An overly rosy view, perhaps, and I don't want to deny the reality of the blogger's experience. Clearly, the person is intelligent and attracted to some aspects of LW discourse while turned off by other aspects.