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  • In October 2004, our understanding of the human family tree was turned upside down.

  • That’s when anthropologists reported that they’d discovered the bones of a tiny, unknown

  • hominin, on the Indonesian island of Flores.

  • This little creature stood only about a meter tall and had a brain about the size of a chimpanzee’s.

  • But that wasn’t what was so shocking.

  • We already knew about small-bodied, small-brained hominins in the human fossil record, like

  • the australopithecines.

  • What was really striking about this skeleton is that, at first at least, it appeared not

  • to have been very old, and yet it had features of much older, more basal hominins.

  • The original description of the bones dated them to between about 35,000 and 14,000 years

  • ago, which means that they would have lived at the same time as us.

  • But the last time a hominin with a brain that small was around, was millions of years ago

  • - not thousands - well before modern Homo sapiens was on the scene.

  • And the rest of its skeleton was equally baffling.

  • Its shoulder joint wasn’t like that of any modern human.

  • It had short collarbones, which meant that the shoulders were rotated forward in a way

  • that hadn’t been seen since early specimens of Homo erectus, from around 1.6 million years

  • ago.

  • The three bones of its wrist that were found were also strangely archaic-looking.

  • They were shaped like the bones of African apes and australopithecines - not like ours.

  • And its feet were really long compared to the length of its legs.

  • Were talking ape-like, not human-like, proportions.

  • And yet, it had short big toes and was probably an effective bipedal walker.

  • Its discoverers named this puzzling hominin Homo floresiensis, but it’s often called

  • the hobbitfor its short stature and oddly proportioned feet.

  • And it’s been at the center of a major controversy in the field ever since.

  • It’s been fifteen years now since its discovery was first announced, and were still exploring

  • what this little hobbit can tell us about the shape of the human family tree, and what

  • it means for our own evolutionary history.

  • And the questions that this little creature raises are big:

  • Was it its own species?

  • Or was it really just one of us?

  • Or, could it even have descended from a whole lineage of hominins that we don’t even know

  • about?

  • The partial skeleton that started the whole controversy is called LB1.

  • And it belonged to an adult female Homo floresiensis, based on the shape of her pelvis and the fact

  • that her wisdom teeth had come in.

  • But she’s not the only hobbit that anthropologists have found.

  • Since her discovery, the remains of as many as 11 other members of her species have been

  • recovered, although LB1 is still the only one with a skull.

  • And all of these hobbits come from a single site: a limestone cave called Liang Bua, located

  • in the western part of the island of Flores.

  • So, when LB1 was discovered in 2003, one of the first things scientists had to figure

  • out was how to explain her tiny size and strange mix of features.

  • What branch of our family tree couldve produced such an odd hominin - a hominin,

  • by the way, being a primate that’s more closely related to us than to chimps?

  • The team suggested that her species had evolved from a population of Homo erectus that became

  • isolated on the island of Flores.

  • And then, thanks to evolutionary pressures, their bodies got smaller over time.

  • Now, there are fossils of Homo erectus from other Indonesian islands, and they cover a

  • wide range of time -- from 1.6 million to just 143,000 years ago.

  • So we know that Homo erectus made it to that part of the world.

  • And we know that mammals on islands can change dramatically in body size over time, thanks

  • to a phenomenon known as Foster’s rule, which weve talked about before.

  • This rule says that big mammals on islands often get smaller, and small mammals tend

  • to get bigger, as they adapt to limited resources and fewer predators.

  • So in the original paper about the hobbit’s discovery, the researchers proposed that a

  • group of Homo erectus somehow got stuck on Flores, and they eventually evolved into a

  • new species: the smaller Homo floresiensis.

  • And, Flores wouldn’t have been a terrible place to be stranded.

  • Today, it’s a forested tropical island, and it seems to have been pretty similar,

  • if more variable, while Homo floresiensis was around.

  • Now, it’s not clear whether the hobbits actually lived in the cave where their remains

  • were found.

  • But, based on the number of animal bones and stone tools found in different layers of the

  • site, they seem to have used the cave more when the environment was wetter, and less

  • when it was drier and less forested.

  • And the hobbits seem to have had a ratherexotic diet, at least by our standards.

  • The animal remains found in the cave include a lot of very young pygmy Stegodon, an elephant

  • relative that, like the hobbits, seems to have evolved into a smaller version of its

  • mainland cousins.

  • A number of these bones have cut-marks on them, and some are even burned, so Homo floresiensis

  • seems to have been able to use fire.

  • And there were also lots of bones of Komodo dragons, which are still formidable predators

  • today.

  • It’s not clear whether the hobbits were hunting the Komodo dragons or just scavenging

  • them - but it’s possible that the hobbits might have been hunted by the dragons!

  • Interestingly enough, there don’t seem to be any bones of adult pygmy Stegodon in the

  • cave, which suggests that the hobbits might not have been able to take down a full-grown

  • elephant.

  • The hobbits also left behind a number of simple stone tools, like cores, flakes, and points,

  • some of which seem to have been used not only for hunting, but also for processing plant

  • materials.

  • But other experts weren’t convinced that these artifacts had been made by a new species

  • of hominin.

  • Instead, they thought the so-called hobbits were actually modern Homo sapiens, but from

  • a population of very small-bodied people, like some groups of tropical hunter-gatherers

  • today.

  • And, they argued, LB1 likely had some kind of pathological condition.

  • To support their case, these researchers compared the bones from LB1 with the skeletons of various

  • indigenous peoples of Indonesia and Australia.

  • Their thinking was that the best populations to compare them to would be ones that lived

  • in the same region and environments as the hobbit.

  • And, they said, more than 140 features of LB1’s skull matched those of modern humans

  • from the area.

  • But the researchers who thought Homo floresiensis was a new species countered this argument.

  • They said that there are a number of groups of people from around the world who have adapted

  • to their environments by becoming smaller - but none of them ended up with the same

  • tiny brain and odd limb proportions as the hobbit.

  • So that just left the claim that LB1 was an individual with some kind of pathological

  • condition.

  • In a series of papers, the supporters of this hypothesis proposed a number of different

  • conditions that might explain LB1’s very small skull, short stature, and other features.

  • These included Laron Syndrome, which is caused by an insensitivity to certain growth hormones,

  • as well as microcephaly, or having a much smaller-than-average head circumference, and

  • Down Syndrome.

  • And every time, the scientists who thought Homo floresiensis was a new species pointed

  • out that none of the proposed disorders quite matched LB1’s anatomy.

  • Plus they didn’t explain all of the hobbit’s features that resembled those of older hominins,

  • like its archaic-looking wrist bones.

  • The two camps went back and forth, publishing paper after paper, questioning each other’s

  • arguments - and not always in civil terms.

  • And while one group of researchers still thinks LB1 is a pathological modern human, some recent

  • work has suggested a third theory of where the hobbits came from.

  • The Shire!

  • No, just kidding

  • Instead of being a dwarfed version of Homo erectus, or a modern human with a developmental

  • disorder, maybe the hobbit actually evolved from another, earlier hominin species -- one

  • we don’t know about yet.

  • In this scenario, Homo floresiensis is still its own, new species, but its ancestor wasn’t

  • Homo erectus.

  • And in 2017, some experts tested this hypothesis.

  • They collected a whole lot of skeletal data from 11 different hominin species, and built

  • two kinds of evolutionary trees that showed how the species might be related.

  • One tree was designed around the notion of parsimony, the idea that the simplest path

  • for one species to diverge into another is the one with the fewest changes in features.

  • The other model was built using statistics, analyzing how likely a path might be, based

  • on different models of evolutionary change.

  • And both methods came up with pretty similar results.

  • In one scenario, Homo floresiensis shared a common ancestor with Homo habilis, a hominin

  • that lived in Africa between 2.4 million and 1.4 million years ago.

  • In the other scenario, the hobbits are part of the sister group to the branch that includes

  • Homo habilis, Homo erectus, and us.

  • What all this suggests is that Homo erectus might not have been the first hominin to leave

  • Africa - even though that’s what the current fossil record shows.

  • It also suggests that there’s probably a lot of ancestors on the hobbit’s branch

  • of the family tree that are still out there, waiting to be found.

  • Which is amazing even to think about, there’s so much we don’t know!

  • Now where does the debate about the hobbit stand today?

  • Well, the consensus among most experts is that Homo floresiensis is probably its own,

  • unique species.

  • This was helped along by the publication of revised dates for the bones and stone artifacts

  • that were found in the cave.

  • Instead of the dating to between 35,000 and 14,000 years ago, as we first thought, the

  • deposit that the skeleton came from was more like 100,000 to 60,000 years old.

  • And the stone artifacts were between 190,000 and 50,000 years old.

  • So the odd little skeleton was older than we originally thought, which made its archaic-looking

  • anatomy somewhat easier to understand.

  • And it looks like there were changes in the island’s climate and volcanic eruptions

  • around 50,000 years ago, which might explain why the species disappeared.

  • But who it’s descended from is still a wide-open question.

  • And the more digging we do in Southeast Asia, the more complicated our evolutionary story

  • seems to be.

  • For example, in 2019, scientists working in the Philippines announced their discovery

  • of teeth and bones from a new species of hominin dated to about 50,000 to 67,000 years old.

  • It was named Homo luzonensis, and it overlapped in time with the hobbits and us, along with

  • some of our other extinct relatives.

  • And it had a different mix of ancient and modern features than the hobbit, like very

  • small molars but with larger premolars, and curved finger bones.

  • This discovery -- of another new hominin on a remote island in Southeast Asia-- just reinforces

  • how much more we have to learn about our family tree.

  • Excavations at the cave where the original hobbit was found are on-going.

  • And anthropologists are trying all the latest genetic techniques to try to unravel the mystery

  • of the hobbit at the molecular level.

  • But so far, our attempts to extract DNA from the hobbit’s bones have failed, because

  • hot, humid caves are just terrible for preserving DNA.

  • But even newer methods, like extracting ancient proteins, like collagen, from the bones have

  • yet to be tried.

  • So maybe there’s still some hope for figuring out where Homo floresiensis fits into our

  • family tree.

  • And maybe that will help us better understand this particular chapter of human evolution,

  • back in the time when hobbits were real.

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当霍比特人是真实的(When Hobbits Were Real)

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    joey joey 發佈於 2021 年 05 月 04 日
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