A paper published Tuesday in the PLoS Biology scientific journal shows that African elephants are, in fact, two species that diverged millions of years ago.
"A surprising finding from our study is that the divergence of African savanna and forest elephants -- which some have argued to be two populations of the same species -- is about as ancient as the divergence of Asian elephants and mammoths," according to the authors, who are made up of researchers from the United States, United Kingdom and Germany. "Given their ancient divergence, we conclude that African savanna and forest elephants should be classified as two distinct species."
Modern savanna (or bush) elephants weigh roughly twice as much as their forest-dwelling cousins, and have significantly different body shapes, with the savanna breed standing nearly a meter taller than the forest elephants.
Mitochondrial DNA analysis proves the forest elephants should be now known as Loxodonta cyclotis and the savanna ones as Loxodonta Africana, the authors say.
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"We'll need to rewrite some basic biology textbooks," said David Reich, lead author of the paper and a geneticist with Harvard Medical School.
The two species can interbreed, but researchers say that such pairings are rare in the wild and the hybrids produced in the matings typically don't pass on their genes.
That could be because the hybrid males are smaller than their savanna rivals, and elephant females usually mate with only the largest bulls, leaving the two populations separate and distinct.
The two lineages diverged genetically between 2.5 and 5 million years ago, roughly the same time that humans and chimpanzees split apart, says Alfred Roca of the University of Illinois.
Huge climatic changes in Africa at the time led some animals to remain in the forests while others took to the vast new grasslands ushered by a drying and warming climate.
Roca says that the study used new technology that allows a much more detailed view of the genetic sequences of the five species they studied and is the first-ever sequencing of the extinct mastodons' nuclear genomes.
After studying elephant genetics for 13 years, Roca says he was still surprised to find the results showed that the savanna and forest elephants are roughly as distant genetic cousins as modern Asian elephants are to the now-extinct woolly mammoths.
The findings could lead ecologists and governments to change the way they are trying to protect elephants in Africa, with much more focus on developing distinct species-specific conservation plans.
Roca says that the forest elephants make up about a fifth of the continent's elephant population, but are under far more environmental pressure due to deforestation and competition with rising populations of humans.
"From the standpoint of protecting the animals, the savanna elephants have been the poster child of conservation efforts," Reich says. "These new findings show that losing the forest elephants would be a major loss and extinction as well."
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