Female giraffes drove the evolution of long giraffe necks in order to feed on the most nutritious leaves, new research suggests

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Douglas R. Cavener, Penn State

(THE CONVERSATION) Everything in biology ultimately boils down to food and sex. To survive as an individual you need food. To survive as a species you need sex.

Not surprisingly then, the age-old question of why giraffes have long necks has centered around food and sex. After debating this question for the past 150 years, biologists still cannot agree on which of these two factors was the most important in the evolution of the giraffe’s neck. In the past three years, my colleagues and I have been trying to get to the bottom of this question.

Necks for sex

In the 19th century, biologists Charles Darwin and Jean Baptiste Lamarck both speculated that giraffes’ long necks helped them reach acacia leaves high up in the trees, though they likely weren’t observing actual giraffe behavior when they came up with this theory. Several decades later, when scientists started observing giraffes in Africa, a group of biologists came up with an alternative theory based on sex and reproduction.

These pioneering giraffe biologists noticed how male giraffes, standing side by side, used their long necks to swing their heads and club each other. The researchers called this behavior “neck-fighting” and guessed that it helped the giraffes prove their...