Researcher who tracked DNA finds army ants evolved just once

WASHINGTON -- Army ants that sweep along in massive, voracious groups evolved just once, contrary to common scientific belief, a Cornell University researcher says.

Entomologist Sean Brady studied the DNA of 30 army ant species from across the world and concluded that they all had the same point of origin.

Brady's findings, scheduled for this week's online edition of Proceedings of the National Academy of Sciences, were being released early, the academy said last week.

Scientists have thought that army ants originated separately on different continents over millions of years.

Brady's findings indicate that the ants have existed 100 million years -- since the reign of dinosaurs -- and haven't changed.

"I didn't think they'd be that old. ... It's kind of amazing that for tens of millions of years they were engaged in their hunting parties when dinosaurs were walking all over them," Brady said.

At the time they evolved, the southern continents were formed a massive landmass known as Gondwana, which has since broken up.

"Biologists have wondered why army ants, whose queens can't fly or get caught up in the wind, are yet so similar around the world," Brady said.

There was no strong theory of separate evolution, he said. The idea was based merely on the assumption they evolved more recently and thus must have done so separately. Brady said he wanted to test that idea with his study.

Unlike common ants, army ants are nomadic, they forage without advance scouts and their wingless queens produce millions of eggs every month.

Brady said that while studying army ant DNA he was able to build a "family tree" for the creatures. Combining this with studies of the ants' form and structure, he found that all the species share the same genetic mutations, evidence all evolved from the same source.