Gibbons, the first apes to break from the evolutionary line that eventually led to us humans, have mysterious "scrambled" DNA that may have led to their evolving as new species, scientists report.

A massive reshuffling of the DNA was discovered by U.S. researchers sequencing of the genome of the endangered small apes living in Southeast Asian tropical rainforests.

The found an extraordinary amount of what are termed chromosomal rearrangements, which are structural modifications in DNA that can cause problems in many other species -- including leading to cancer in humans -- but which seem to have helped gibbons evolve and adapt to their environments, the researchers report in the journal Nature.

"This 'genome plasticity' has always been a mystery," says Wesley Warren of Washington University at St. Louis.

In sequencing the genome, the researchers discovered a portion of DNA they dubbed LAVA occurring more than a thousand times in the genome.

Apparently unique to the gibbon genome, LAVA is what is known as a retrotransposon, which affects genes controlling how chromosomes are paired up during the process of cell division.

LAVA has made the genome of gibbons unstable and subject to dramatic changes, the researchers say.

Such extreme changes in most species' genomes are normally linked with deleterious effects such as increases in maladies such as cancer, leading the researchers to wonder why that hasn't been the case in gibbons.

"It's a complete mystery still how these genomes are able to pass from one generation to the next and not cause any major issues in terms of survival of the species," says Warren.

It could be the case that some genomes are more resilient than has previously been thought, says James Shapiro of the University of Chicago.

"The genome can endure lots of changes and still function."

Shapiro is among an increasing number of scientists who suggest major genome shuffling has played a crucial part in evolutionary history, playing a major role in the forming of new species.

The first gibbon species may have broken away from the lineage out of which humans eventually emerged during just such a major shuffling of the genome, he says.

The research can yield insights into the evolutionary history of both gibbons and humans, and may yield clues to how human diseases have developed, the scientists say.

"We do this work to learn as much as we can about gibbons, which are some of the rarest species on the planet," says Lucia Carbone of Oregon Health and Science University, who led the analysis of the gibbon genome. "But we also do this work to better understand our own evolution and get some clues on the origin of human diseases."

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