WASHINGTON, Feb. 26 (Xinhua) -- An international team has produced comprehensive evolutionary pictures about elephants and their relatives, mammoths and mastodons, that span millions of years.

The study, published on Monday in the Proceedings of the National Academy of Science, suggests that interbreeding helps explain why mammoths were so successful in diverse environments and for a long time.

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

The study shed light on a complicated history, characterized by widespread interbreeding.

"This genomic data tells us that... evolution doesn't happen in an organized, linear fashion," said evolutionary geneticist Hendrik Poinar, one of the paper's senior authors and director of the McMaster Ancient DNA Center in Canada.

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

"This is one of the oldest high-quality genomes that currently exists for any species," said Michael Hofreiter at the University of Potsdam in Germany, a co-senior author who led the work on the straight-tusked elephant.

Researchers also found further evidence of interbreeding among Columbian mammoths and woolly mammoths.

Despite their vastly different habitats and sizes, researchers believe that woolly mammoths encountered Columbians mammoths at the boundary of glacial and in the more temperate ecotones of North America.

However, they 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.

Interbreeding among closely related mammals is fairly common, according to researchers, who point to examples of brown and polar bears, Sumatran and Bornean orangutans, and the Eurasian gold jackals and grey wolves. A species can be defined as a group of similar animals that can successfully breed and produce fertile offspring.

Researchers suggest that they would explore whether the introduction of new genetic lineages into elephant populations, both living and ancient, which played an important role in their evolution, allows them to adapt to new habitats and fluctuating climates.