There are a couple of books which I can recommend that talk about why you see so few women in computing (as opposed to biology, math, etc) and also why you see so few black men and women:
* Unlocking the Clubhouse: http://a.co/8oXDROX
* Stuck in the Shallow End: http://a.co/9HXgvKW
These are not only well written, but they're also well researched and well thought out. They're worth reading on their own merits, but you may find them a useful debunking to the memo.