Mystery of horned females solved

It was one of the many mysteries pondered by Darwin: why do some female animals have horns?

Horns on cloven-hooved mammals are thought to have evolved for fighting each other, but most female cattle and deer don't do this.

Now Theodore Stankowich of the University of Massachusetts and Tim Caro from the University of California, Davis, have a solution. They noted the presence or absence of horns in 117 species of bovid and set up competing mathematical models to examine whether evolution of horns was likely to have been driven by body size, openness of habitat, territorial behaviour, group size or conspicuousness.

This showed that horns were most likely in conspicuous species - those living in open habitats and large enough to be clearly visible to predators - suggesting that they evolved as defensive weapons.

Behavioural ecologist Craig Roberts of the University of Liverpool, UK, is not convinced.

"They haven't shown that female competition for food could not be the reason why horns evolved.", Roberts told New Scientist magazine, which also announced the results of the researches done by Stankowich and Caro.