The study revealed interbreeding was widespread in the history of these animals. (Photo: Pixabay)

A new study now finds that there are just two African elephant species, forest and savanna elephants - and they don't interbreed.

The research adds to growing fears regarding the future of the few species that remain on Earth.

The study, published in the journal Proceedings of the National Academy of Science, was conducted by a team of scientists from McMaster University, the Broad Institute of MIT and Harvard, Harvard Medical School, Uppsala University,and the University of Potsdam.

The team painstakingly sequenced 14 genomes, from both living and extinct species from Asia and Africa, two American mastodons, a 120,000-year-old straight-tusked elephant, and a Columbian mammoth.

What the study revealed was that interbreeding was widespread in the history of these animals.

However, this has virtually stopped.

Speaking about it, evolutionary geneticist Hendrik Poiner, who is one of the senior authors on the paper and Director of the McMaster Ancient DNA Centre and principal investigator at the Michael G. DeGroote Institute for Infectious Research said, “Interbreeding may help explain why mammoths were so successful over such diverse environments and for such a long time, importantly this genomic data also tells us that biology is messy and that evolution doesn't happen in an organized, linear fashion.”

He added that the combined analysis of genome-wide data from all these ancient elephants and mastodons has raised the curtain on elephant population history, revealing complexity that scientists were not aware of earlier.

For example, a DNA analysis of the ancient straight-tusked elephant showed that it was a hybrid with portions of its genetic makeup stemming from an ancient African elephant, the woolly mammoth, an present-day forest elephants.

Researchers also found further evidence of interbreeding among the Columbian mammoths (which covered the present day United States as far south as Nicaragua and Honduras) and woolly mammoths, which arose in Eurasia.

Surprisingly, scientists found no genetic evidence of interbreeding among two of the world's three remaining species, the forest and savanna elephants, suggesting they have lived in near-complete isolation for the past 500,000 years, despite living in neighboring habitats.

The finding is surprising because interbreeding among closely related mammals is fairly common.

'This paper, the product of a grand initiative we started more than a decade ago, is far more than just the formal report of the elephant genome,' said co-senior author Kerstin Lindblad-Toh, a senior associate member of the Broad Institute and Director of the Science for Life Laboratory at Uppsala University in Sweden.”

She further added, “It will be a reference point for understanding how diverse elephants are related to each other and it will be a model for how similar studies can be done in other species groups.”

The researchers suggest that future work should explore whether the introduction of new genetic lineages into elephant populations - both living and ancient - played an important role in their evolution, allowing them to adapt to new habitats and fluctuating climates.