Seems to me the horn thing was debunked a while ago, but it got me wondering.

If you irritate bone regularly, it'll start to form a little bump. So if you kept doing it, and it was part of your culture or something, maybe part of the royalty process, maybe it would be possible, after long enough and with considerable practice to get it right, to actually "grow" horns like that.

I'm assuming that it would take generations and a lot of patience, but after a while, like those girls in Africa with the rings around their necks, maybe some folks came up with a tradition of growing horns.

It would probably be quite the advantage, for a while, when it came to fighting other tribes, because you'd look like devils or whatever. On the downside, that fear might ensure your extermination eventually, when enough others banded up to "kill the devils".