Why do some bulls have a hump?

Why do some bulls have a hump?
Wildrosebeef Updated Answer
ALL bulls should have a hump or crest. A muscular hump on their necks is a sign of adequate masculinity and good fertility. They are what cattle producers call "superior quality sires." A bull with no or a very small hump on its neck is a bull that is inferior, with poor fertility, poor muscling, and lacking in masculinity. These kind of bulls shouldn't be used for breeding females, and should be slaughtered for beef or sold as bologna bulls.