Have you ever been told that the reason giraffes have such long neck is that they evolved to eat leaves on tall trees? Well, you've been lied to. The real reason (surprise, surprise) is sex and mating:
The latest theory – and it's a surprise this hasn't come up before, given biologists' fixation with it – is that the long necks are the result of sexual selection: that is, they evolved in males as a way of competing for females.
Male giraffes fight for females by "necking". They stand side by side and swing the backs of their heads into each others' ribs and legs. To help with this, their skulls are unusually thick and they have horn-like growths called ossicones on the tops of their heads. Their heads, in short, are battering rams, and are quite capable of breaking their opponents' bones.
Having a long and powerful neck would be an advantage in these duels, and it's been found that males with long necks tend to win, and also that females prefer them.
The "necks for sex" idea also helps explain why giraffes have extended their necks so much more than their legs. If giraffes evolved to reach higher branches, we might expect their legs to have lengthened as fast as their necks, but they haven't.
Previously on Neatorama: 30 Strangest Animal Mating Habits