Since the discovery in 2007 of Callao Man — represented by a Homo sapiens foot bone excavated at Callao Cave — humans were thought to have first lived in the Philippines about 67,000 years ago.

Now that number needs to be multiplied nearly 11 times, as an international team of researchers has just discovered strong evidence that early humans were in the Philippines by at least 709,000 years ago. The evidence, reported in the journal Nature, consists of 57 stone tools and an almost complete disarticulated skeleton of a butchered rhinoceros.

"There are obviously two questions to answer at present," lead author Thomas Ingicco of the National Museum of Natural History in Paris told Seeker. "One is who made the stone tools and butchered the rhino."

"The other question is the origin of the dispersion," he added, referring to how the toolmakers and rhino wound up in a bucolic part of the Philippines.

The new findings, as well as prior research, provide clues.

First, there is the location of the artifacts and animal bones, which also include the remains of brown deer, monitor lizards, freshwater turtles, and stegodons — members of an extinct genus similar to elephants and mammoths. All were found at a site called Kalinga in the Cagayan Valley of northern Luzon Island, Philippines.

"By 700,000 years ago, Homo erectus seems to have been present everywhere in Asia," Ingicco said. "We have fossils from China and Java in Indonesia, and some are much older than the Kalinga site as we have evidence as early as 1.8 million years ago in those places."

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The Kalinga toolmakers therefore could have been Homo erectus individuals. They might have traveled to the Philippines along one of four possible gateways, according to Ingicco and his team. The first, a northern route, is from China via Taiwan. The second, a southern approach, is from Sulawesi via the Sangihe Islands. The third, a southwestern route, is from Borneo via the Sulu Archipelago, and the fourth, a northwestern approach, is from Borneo via Palawan Island.

The trip perhaps was not intentional.

"Colonization of the islands could have been possible thanks to natural rafts, such as floating mangroves that typhoons occasionally break off the coast," Ingicco said. "These floating islands would have come with animals and possibly hominins (early humans) on them. Such natural rafts are quite well documented for historical periods and it is therefore a likely way of colonizing Luzon Island during the mid-Pleistocene by hominins."

He added, however, that "floating islands cannot be recovered by archaeological means nor can some kind of watercraft for such an old archaeological site."

The latter is important, because the scientists cannot rule out that the Kalinga toolmakers constructed their own boat, raft, or other means of water transportation. The distance then was too far for human swimming, so the scientists can at least negate that idea.

"If these hominins were capable of constructing some sort of watercraft, then it would indeed be an extraordinary discovery," Ingicco said.