Friend or foe? Elephants run from the voices of Maasai men, such as this herder (top).

Friend or foe? Elephants run from the voices of Maasai men, such as this herder (top).

(Top) Graeme Shannon; (Bottom) Karen McComb

ScienceShot: Elephants Shaped Their Own Evolution

Modern African elephants have teeth designed for grazing—perhaps because their ancestors sought out new dining experiences millions of years ago, according to a study in today's issue of Nature. Beginning about 10 million years ago, East Africa began to change from woodland to drier grassland. The elephants' teeth changed as well; the crowns of molars became up to three times higher, and the teeth developed more of the enamel ridges that allowed the animal to grind grass, which is tougher than leaves and often laden with grit. To explore how well the timing of the changes matched up, the researcher focused on a carbon isotope called 13C, which is retained in soil in the same proportions as in the vegetation the soil once contained. By checking published literature for records of 13C in both soil and elephant fossils spanning some 20 million years, he found that many elephants and related species switched from browsing to grazing about 8 million years ago, when the terrain was still a mosaic of both woodland and grassland. Yet the changes in the teeth didn't appear for another 3 million years. The finding suggests that the elephants tried out new feeding areas and new types of food, thus putting themselves in a position where natural selection would favor individuals with better-adapted teeth. By challenging the more passive view of natural selection—in which an environmental change simply favored elephants with stronger teeth—the study uses fossil evidence to show that the animals' own behavior may have helped shape their evolutionary destiny.

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