Fossils from a Philippine cave may come from a new human-like species | Science News for Students

Fossils from a Philippine cave may come from a new human-like species

Scientists say Homo luzonensis lived at least 50,000 years ago
May 10, 2019 — 6:45 am EST
a photo of the inside of a Phillipine cave

Scientists think fossils from this Philippine cave were left by a previously unknown Homo species that lived at least 50,000 years ago.

Callao Cave Archaeology Project

In a cave in the Philippines, researchers made a remarkable discovery of fossil bones and teeth. These remains appear to come from a new human-like species.

This human relative, or hominid, lived at least 50,000 years ago. Scientists have just dubbed its species Homo luzonensis (Lu-zo-NEN-sis). They took the name from Luzon, the island on which the fossil remains were found. Researchers described shared their new findings in the April 11 Nature.

Homo luzonensis lived at the same time as Homo floresiensis (Flo-res-ee-EN-sis). Nicknamed “hobbits,” those were controversial, half-sized Indonesian hominids who roamed its island of Flores.

Some of the new fossil bones are similar in shape and size to those in other Homo species. “But if you take the whole combination of features for H. luzonensis, no other Homo species is similar,” says study coauthor Florent Détroit. He’s a paleoanthropologist (PAY-lee-oh-an-throh-PAAL-oh-gizt) at the French National Museum of Natural History in Paris.

It will take more research to confirm that this is truly a new species. But if true, it would add another twist to the story of human evolution in Asia. Modern humans, Homo sapiens, reached what’s now Southern China between 80,000 and 120,000 years ago. When they got there, other members of the Homo genus were already living in East Asia and on Southeast Asian islands. As researchers gather fossils and DNA evidence, the story is becoming more complex.

What the bones say

Researchers dug in Luzon’s Callao Cave in 2007, 2011 and 2015. They found a dozen H. luzonensis fossils. These included seven teeth, five of which came from just one individual. They also found two finger bones and two toe bones. And they dug up an upper leg bone missing its ends.

To date how old the fossils were, scientists analyzed the radioactive decay of uranium in one tooth. (This element decays at a constant rate.) This suggested the bones are at least 50,000 years old. Based on that date, researchers decided a bone from another 2007 dig there also belonged to H. luzonensis. That was a foot bone found in the same cave sediment. It’s at least 67,000 years old.

a photo of five fossil teeth
These five fossil teeth, dug up in the Philippines, all came from one individual. Their distinct mix of traits led researchers to declare the species that left them a new human-like relative.
Callao Cave Archaeology Project

In some ways, the teeth have traits seen in modern humans. But in other ways they resemble ancient, now-extinct hominids. For example, H. luzonensis had molars that were very tiny, even smaller than those in hobbits. But the molars also have some features similar to those in modern humans. Other teeth, called premolars, were relatively large in H. luzonensis. Surprisingly, these teeth had two or three roots. Those teeth in modern humans have only one root. But hominids that lived at least several hundred thousand years ago — such as Homo erectus — typically had premolars with multiple roots.

Finger and toe bones in H. luzonensis are curved. That suggests these individuals could climb trees. In this way, they would resemble hominids from at least 2 million years ago.

It's unclear whether H. luzonensis was as small as hobbits, Détroit says. The best-preserved hobbit skeleton comes from a female. She stood only about one meter (three feet) tall. Based on the length of the Callao Cave foot bone, Détroit’s team suspects that H. luzonensis was taller than that. But these people still would have been smaller than most human adults today.

Mysterious origins

As with hobbits, the evolutionary origins of H. luzonensis are a mystery. Scientists think hobbits may have descended from groups of H. erectus that traveled the seas. Perhaps H. luzonensis did too, writes Matthew Tocheri. He’s a paleoanthropologist at Lakehead University in Thunder Bay, Canada. Tocheri wrote a commentary that was also published in the April 11 Nature.

Evidence suggests that hominids reached Luzon by around 700,000 years ago. Détroit speculates that H. erectus may have also crossed the sea to Luzon from other Indonesian islands or from mainland Asia. Then it might have evolved into H. luzonensis, with its smaller body and unusual skeletal traits. This is a process known as island “dwarfing.”

But some scientists who weren’t part of the new study say it’s too soon to call the Luzon fossils a brand-new Homo species. Détroit’s group has not extracted DNA from the fossils. Until they do, “all [evolutionary] possibilities must remain open,” says Katerina Douka. She’s an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany.

The fossils have a mix of features that the team finds distinctive. But maybe that mix came from two or more earlier Homo species interbreeding. That would mean the fossils are hybrids, not a new species.

Or the Luzon hominids might have started out as a small population of, say, H. erectus. As they survived on the island for possibly hundreds of thousands of years, perhaps they evolved some new skeletal traits. But that wouldn’t necessarily make them a new species, says paleoanthropologist María Martinón-Torres. She directs the National Research Centre on Human Evolution in Burgos, Spain.

Such questions make the new fossils “an exciting and puzzling discovery,” Martinón-Torres says.

Scientists know for sure that the Callao Cave hominids had unusual teeth. They also had hand and foot bones built for climbing. If Luzon’s ancient Homo members all shared these traits, “then that combination is unique and unknown so far” among hominids, Martinón-Torres says. A more complete set of fossils, ideally with ancient DNA, would tell us more. Martinón-Torres says we’ll need these findings to know for sure whether our family tree has a new member.

Power Words

(more about Power Words)

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

commentary     (in science) An opinion piece, often written to accompany — and add perspective to — a paper by others, which describes new research findings.

constant     Continuous or uninterrupted.

decay     The process (also called “rotting”) by which a dead plant or animal gradually breaks down as it is consumed by bacteria and other microbes. (for radioactive materials) The process whereby a radioactive isotope — which means a physically unstable form of some element — sheds energy and subatomic particles. In time, this shedding will transform the unstable element into a slightly different but stable element. For instance, uranium-238 (which is a radioactive, or unstable, isotope) decays to radium-222 (also a radioactive isotope), which decays to radon-222 (also radioactive), which decays to polonium-210 (also radioactive), which decays to lead-206 — which is stable. No further decay occurs. The rates of decay from one isotope to another can range from timeframes of less than a second to billions of years.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).

evolutionary     An adjective that refers to changes that occur within a species over time as it adapts to its environment. Such evolutionary changes usually reflect genetic variation and natural selection, which leave a new type of organism better suited for its environment than its ancestors. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

extinct     An adjective that describes a species for which there are no living members.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

genus     (plural: genera) A group of closely related species. For example, the genus Canis — which is Latin for “dog” — includes all domestic breeds of dog and their closest wild relatives, including wolves, coyotes, jackals and dingoes.

hobbit     Nickname given to Homo floresiensis, a small-bodied hominid species whose fossils have turned up only on the island of Flores, in Indonesia. The small-brained folk lived in isolation there until at least 18,000 years ago.

hominid     A primate within the animal family that includes humans and their ancient upright-walking relatives. Except for humans, all other hominids are known only from fossils.

Homo     A genus of species that includes modern humans (Homo sapiens). All had large brains and used tools. This genus is believed to have first evolved in Africa and over time evolved and radiated throughout the rest of the world.

Homo erectus     An extinct species of hominid that lived in Africa and Eurasia between about 1.9 million and 70,000 years ago.

hybrid     An organism produced by interbreeding of two animals or plants of different species or of genetically distinct populations within a species. Such offspring often possess genes passed on by each parent, yielding a combination of traits not known in previous generations. The term is also used in reference to any object that is a mix of two or more things.

paleoanthropologist     A scientist who studies ancient humans and hominid biology, also the behavior and evolution of hominids evolved. This field is based on the analysis of fossils, remnants, artifacts or markings created or used by hominids.

population     (in biology) A group of individuals from the same species that lives in the same area.

premolar     Also known as a bicuspid, this is one of the teeth located between the so-called canine tooth and the molars. Adult humans have two premolars on each side of the upper and lower jaws.

radioactive     An adjective that describes unstable elements, such as certain forms (isotopes) of uranium and plutonium. Such elements are said to be unstable because their nucleus sheds energy that is carried away by photons and/or and often one or more subatomic particles. This emission of energy is by a process known as radioactive decay.

radioactive decay     A process by which an element is converted into a lighter element through the shedding of subatomic particles (and energy).

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sediment     Material (such as stones and sand) deposited by water, wind or glaciers.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

unique     Something that is unlike anything else; the only one of its kind.

uranium     The heaviest naturally occurring element known. It’s called element 92, which refers to the number of protons in its nucleus. Uranium atoms are radioactive, which means they decay into different atomic nuclei.

Citation

Journal: F. Détroit et al. A new species of Homo from the Late Pleistocene of the Philippines. Nature. Vol. 568, April 11, 2019, p. 181. doi:10.1038/s41586-019-1067-9.

Journal: M. Tocheri. Previously unknown human species found in Asia raises questions about early hominin dispersals from Africa. Nature. Vol. 568, April 11, 2019, p. 176.