Inbreeding, hybridization, and isolation all play a role in the evolution of elephants, findings of a new study published in the Proceedings of the National Academy of Science have revealed.

Study researcher Eleftheria Palkopoulou from Harvard Medical School and colleagues found that ancient elephant species practiced widespread interbreeding, which likely helped these animals survive in a wide variety of environments.

DNA Analysis Revealed Ancient Elephant Species Interbred

Palkopoulou and colleagues sequenced the genomes of 14 different species of elephants, which include both living and extinct species from Africa and Asia. They also sequenced the genomes of two American mastodons, straight-tusked elephants that once lived in Asia and Europe, and a Columbian mammoth.

The findings revealed that the ancient straight-tusked elephant was a hybrid, with portions of its genome stemming from the woolly mammoth, the ancient African elephant, and the present-day African forest elephants.

Researchers traditionally thought that closest relative of the straight-tusked elephants was the Asian elephants because of the similarities in their teeth and skulls.

"We were puzzled by the discrepancy between morphological and genetic results, but our analyses show that the ancestry of straight-tusked elephants was highly composite including three ancestral components," said Palkopoulou.

DNA analysis also provided evidence suggesting that the Ice Age Columbian and woolly mammoths interbred. Interestingly the researchers did not find genetic evidence that there was interbreeding between the present-day forest and savanna elephants. What this suggests is that these two living species thrived in near-complete isolation for the past 500,000 years.

"While hybridization events have shaped elephantid history in profound ways, isolation also appears to have played an important role," the researchers wrote in their study. "Our data reveal nearly complete isolation between the ancestors of the African forest and savanna elephants for ∼500,000 y, providing compelling justification for the conservation of forest and savanna elephants as separate species."

Declining Numbers Of Modern-Day Elephants

Researchers of a 2017 study revealed that the population of forest elephants in one of the largest reserves in Central Africa has dropped between 78 and 81 percent because of poaching. The researchers hope that their work can contribute to current efforts to save the elephants amid declining numbers.

"I hope that this study can create an appreciation for the rich evolutionary history of elephants and emphasize the need for protecting the only three elephant species that still walk the planet today, who are all under imminent risk of extinction from poaching and habitat loss," Palkopoulou said.

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