It was a hot and humid day when archaeologists set off for the island of Luzon, the Philippines, in search of historic treasures.
What they eventually found would excite and perplex them in equal measure, a sight they couldn’t have imagined in their wildest dreams.
Locating a remote cave system on the country’s largest island, researchers didn’t have to search for long before finding an altogether new branch of human ancestry.
Small in stature and possessing no distinctive features, the remains of Homo luzonensis, as it was named, represented a lost line in the Homo genus that roamed the island at least 50,000 to 67,000 years ago.
It was identified by a total of seven teeth and six small bones and played host to several ancient and unseen features, though displayed characteristics seen in today’s humans.
The find and its results, published in the science journal Nature in 2019, have kept scientists on their toes ever since.
Yet, in some way, they shouldn’t have been surprised: archaeologists working across Southeast Asia in the last 15 years have consistently found evidence of unexpected human activity, and not of the kind that we know.
The presence of Homo luzonensis could mean that primitive human relatives left Africa and made it to Southeast Asia, something not previously thought possible. The subsequent study shows that human evolution in the region could well have been a highly complex affair.
Three or more human species could have existed in the region around the same time that Homo sapiens — the last surviving species of the Homo genus — first arrived.
The remains retrieved from Callao Cave consist of 13 separate specimens: teeth, hand and foot bones, and part of a femur that belong to at least three adult and juvenile individuals.
Although the results weren’t published until 2019, the remains had been collected since 2007.
Homo luzonensis was a completely different human to that which we know today. It did, however, share a striking number of similarities.
For example, the width of its tooth was shortened considerably compared to its contemporary species, just like that of Homo sapiens. Like other recent modern humans, luzonensis’ molars decrease in size towards the back of the mouth, and its enamel-dentin juncture lacks well-defined wavy crenulations.
This is largely where the likenesses end. Many of its other, more defining features hark back to the days of the australopithecines, an odd species that though walked upright resembled an ape more than a human.
Its finger and toe bones are also curved, hinting that climbing was an integral part of its existence, something that was also the case for australopithecines.
Scientists are most stumped not on the similarities between luzonensis and australopithecines but on its presence in Southeast Asia.
Homo Erectus has long been held as the first member of modern humans’ direct lineage to leave Africa around 1.9 million years ago. But luzonensis’ existence suggests that migration happened perhaps more than two million years ago.
The fact that Luzon has only ever been accessible by sea also raises questions about how luzonensis managed to reach the island in the first place.
The mystery is further compounded by the presence of another human species called Denisovans, a relatively unknown archaic hominin that existed across Europe and Western Asia during the Lower and Middle Paleolithic from 400,000 years ago to 40,000 years ago.
They are thought to have interbred with Homo sapiens when they arrived in the region. How the Denisovans reached the island is again up for debate.
