The researchers also cannot rule out that the Kalinga toolmakers were Homo floresiensis, aka the Hobbit Humans, so named because of their diminutive size and the popularity of "The Lord of the Rings" film series that was in theaters during the time of the hominins' discovery. The island of Flores, where Homo floresiensis remains were found, is just south of the Philippines.
Conversely, the Kalinga toolmakers could have eventually made their way down to Flores, and Homo floresiensis evolved from them. They could have been small even before they took such a hypothetical journey.
Ingicco explained, "Luzon Island might have been the place for similar endemic evolution of hominins into dwarfism, just like what happened on Flores."
Caley Orr of the University of Colorado, Denver has studied Homo floresiensis and other early humans. Orr told Seeker that it has been previously theorized "that a population of Homo erectus was stranded on the island of Flores and became 'dwarfed' over time, which sometimes happens to larger animals that adapt to small island environments."
Orr added, "Homo floresiensis probably went extinct by at least 13,000 years ago." That is relatively recent, in terms of overall human history.
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Ignicco and his colleagues say it is also possible that an entirely different and as-of-yet unknown hominin made the Kalinga tools and was the first to settle the Philippines. The tools unfortunately do not shed light on this matter.
Made from pebbles, the tools were simple in construction but knapped — that is, shaped by striking, which in this case occurred on anvils.
"Anvil technology is actually found in different places around the world, and it seems to always be used whenever the pebbles are too hard to be knapped in these other places," Ignicco said. "In France, for example, anvils were used to produce tools from quartzite by 1.1 million years ago."
One excavated pebble at Kalinga was five times larger than the rest. The researchers do not think that it arrived at the site by natural transport, such as flowing in from a river, so they suspect that it was intentionally brought to the area by the early humans, who perhaps used it as an anvil or in their butchering of the rhino.
The rhino — the now-extinct Rhinoceros philippinensis — appears to have been savored. Cut marks reveal that its consumers likely stripped off the meat and smashed its bones to gain access to the animal's marrow. Remarkably, 75 percent of the rhino's remains were found during the excavation.
Prehistoric human migrants often seemed to adhere to a simple rule: follow the meat — or fish. Evidence is mounting that early humans tracked animal migrations on land, leading them into new territories. During settlement of the Americas, for example, the kelp highway hypothesis holds that some of the first Americans colonized the New World by following coastlines and seafood-rich kelp forests from north to south.
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Since there is a huge time gap between the Kalinga finds and Callao Man's lifetime, the researchers are not certain if the two are connected. The researchers applied three different dating methods to the former, including electron spin resonance used to analyze quartz grains found above and below the archaeological deposit. The methods suggest that the finds could be even older than 709,000 years.
If the Kalinga toolmakers and the population represented by Callao Man remained in the Philippines and produced continuous subsequent generations, people of Philippine descent today could be related to one or both of these groups. In any case, the new finds significantly add to the islands' already rich history.
As Ignicco said, these are "exciting discoveries" that will surely spark intense future research in the Philippines.
Only a few other sites, such as Choukoutien in China and Ngebung in the Sangiran Dome of Java, have yielded evidence for early humans butchering animals in Southeast Asia. The scientists therefore hope to learn much more about the identity, origin, behavior, and diet of hominins from this region who lived during the Middle Pleistocene, 781,000–126,000 years ago.