Homo Floresiensis: The Real-life Hobbits of Indonesia

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Homo Floresiensis: The Real-life Hobbits of Indonesia Oct 10, 2019 23:06:40 GMT

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Post by Admin on Oct 10, 2019 23:06:40 GMT

The Days of Hobbits
The H. floresiensis fossils were found in Liang Bua cave on Flores, a narrow island — about 200 miles long and 40 miles wide — between Southeast Asia and Australia. Initially, researchers reported that the remains dated between 12,000 and 95,000 years old. For an extinct human species, 12,000 years ago is crazy recent — modern humans were building permanent settlements and monuments by then.

It turns out, the sensational dates were wrong. Continued excavations and analysis showed the hobbit fossils derive from sediment layers between 60,000 and 100,000 years old. And artifacts likely made by H. floresiensis extend between 50,000 and 190,000 years ago, suggesting the species was there even further back, even if we haven’t found their bones.

The thought of hobbits persisting until at least 50,000 years ago is nevertheless exciting. They very well could have encountered our own species, Homo sapiens, thought to have reached Australia by 65,000 years ago. Perhaps modern humans, migrating Down Under, met (and maybe killed) hobbits along the way.

A 2016 Nature paper described hobbit-like fossils at Mata Menge, also on Flores, about 45 miles from Liang Bua. The finds included stone tools, a lower-jaw fragment and six tiny teeth, dated to approximately 700,000 years ago — substantially older than the Liang Bua fossils. Although the Mata Menge remains are too scanty to definitively assign them to the species, most anthropologists consider them hobbits.

At a third Flores site, researchers found no human fossils, but uncovered 1 million-year-old stone tools, like those from Liang Bua and Mata Menge. Assuming these artifacts were made by H. floresiensis or its ancestors, the hobbit lineage inhabited Flores at least from 50,000 to 1 million years ago. That’s over a half million years longer than our species has even existed.

Figure 1: SOA-MM4 mandible compared with a Liang Bua H. floresiensis specimen.

Unearthing Little Humans
Digging in Liang Bua since 2001, an international team has uncovered bones from about a dozen hobbits. But the star specimen is called LB1. It’s the most complete individual, comprising a skull, partial pelvis and bones from the limbs, hands and feet. LB1 appears to be a female adult (her wisdom teeth are fully formed), but measured just 3 foot 6 inches tall and weighed 75 pounds — as tall as a present day 4-year-old, but heftier.

Using micro-CT scanning (high resolution 3D X-ray imaging), a 2013 study estimated her brain volume to be about 426 cc (~1.8 cups). Similarly sized brains are characteristic of much earlier human ancestors, such as Australopiths who lived in Africa some 3 million years ago. The global average for modern humans is ~1,350 cc (5.7 cups), over 3 times larger.

Besides their wee bodies and brains, hobbit skeletons show a mix of primitive and modern-looking traits. Like Australopiths and other early hominins, LB1 has ancient features including broad hips, a short collarbone and forward-positioned shoulder. At the same time, the hobbits’ brow ridges, skull thickness and brain shape are more modern, resembling H. erectus and later species.

The Liang Bua team has also dug up more than 20,000 stone tools. Most are made from volcanic rocks, deliberately fractured to have sharp edges for slicing and dicing. This simple technology resembles the earliest widespread style of toolmaking, the Oldowan, made by numerous ancestral species, starting in Africa 2.6 million years ago.

Figure 2: Isolated teeth from Mata Menge.

The Million-Dollar Questions
Big questions persist about the little creatures: Where do they fit in the human evolutionary tree and why did they go extinct?

Anthropologists have put forth three main hypotheses for the hobbits’ evolutionary origins. One idea, which now lacks support, was that the population belonged to our species, Homo sapiens, but suffered from a genetic or metabolic disorder, responsible for their unusual features. Proponents suggested conditions like microcephaly and Down syndrome, but most scientists conclude the physical symptoms of these disorders are not reflected in H. floresiensis‘ skeletal traits. Furthermore, the 700,000-year-old Mata Menge fossils indicate the hobbits were a long-lived lineage, rather than an isolated, diseased community.

That leaves two hypotheses standing: The hobbits were dwarfed H. erectus — taller, brainier ancestors who appeared ~1.8 million years ago — or the descendants of earlier species, with hobbit-like stature.

The dwarfed H. erectus hypothesis is based on the fact that the evolutionary pressures of island life often cause mammals to differ in size from their mainland relatives. Over time, small animals enlarge because there are fewer predators and big species shrink because there are fewer resources. H. erectus fossils at least 1.2 million years old have been found on the nearby island of Java. On Flores the “island rule” led to the evolution of giant rats and pygmy stegodons (an extinct elephant cousin) — why not H. floresiensis from Javanese H. erectus?

Critics say it’s not clear island dwarfing would cause hominins to shrink this particular way, especially when it comes to skulls. There’s an assumption that once our ancestors evolved H. erectus-sized brains, they couldn’t go back. Plus, dwarfing would have occurred in just a few hundred thousand years. Researchers question if this is enough time for such significant evolutionary change.

Figure 3: CT-based reconstruction of SOA-MM1 and the results of Elliptic Fourier Analysis of the molar crown contour.

Alternatively, the hobbits may have descended from tinier, older ancestors such as Homo habilis or Australopiths. The trouble here is no fossils from these species have been found outside of Africa. Scientists doubt they were capable of long-distance migration over land and sea. Even during the Ice Age, when global sea levels were lower, Flores seems to have been nearly 12 miles from the closest neighboring islands.

Abstract
The evolutionary origin of Homo floresiensis, a diminutive hominin species previously known only by skeletal remains from Liang Bua in western Flores, Indonesia, has been intensively debated. It is a matter of controversy whether this primitive form, dated to the Late Pleistocene, evolved from early Asian Homo erectus and represents a unique and striking case of evolutionary reversal in hominin body and brain size within an insular environment1,2,3,4. The alternative hypothesis is that H. floresiensis derived from an older, smaller-brained member of our genus, such as Homo habilis, or perhaps even late Australopithecus, signalling a hitherto undocumented dispersal of hominins from Africa into eastern Asia by two million years ago (2 Ma)5,6. Here we describe hominin fossils excavated in 2014 from an early Middle Pleistocene site (Mata Menge) in the So’a Basin of central Flores. These specimens comprise a mandible fragment and six isolated teeth belonging to at least three small-jawed and small-toothed individuals. Dating to ~0.7 Ma, these fossils now constitute the oldest hominin remains from Flores7. The Mata Menge mandible and teeth are similar in dimensions and morphological characteristics to those of H. floresiensis from Liang Bua. The exception is the mandibular first molar, which retains a more primitive condition. Notably, the Mata Menge mandible and molar are even smaller in size than those of the two existing H. floresiensis individuals from Liang Bua. The Mata Menge fossils are derived compared with Australopithecus and H. habilis, and so tend to support the view that H. floresiensis is a dwarfed descendent of early Asian H. erectus. Our findings suggest that hominins on Flores had acquired extremely small body size and other morphological traits specific to H. floresiensis at an unexpectedly early time.

Nature volume 534, pages245–248 (09 June 2016)

Last Edit: Apr 22, 2022 22:12:36 GMT by Admin

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Homo Floresiensis: The Real-life Hobbits of Indonesia Oct 11, 2019 4:39:23 GMT

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Post by Admin on Oct 11, 2019 4:39:23 GMT

Because no one has yet successfully extracted DNA from H. floresiensis remains, the researchers couldn't directly compare ancient and modern DNA. Instead, they searched for hobbit traces using a slightly different tack, by asking the question: “What do we find that we can't explain?” says Green. “And the answer is: nothing that looks like what we expect a hobbit to look like.”

This analysis suggests that the Rampasasa people can trace a large part of their ancestry to Near Oceania, a region that includes Papua New Guinea, the Solomon Islands, and the Bismarck Archipelago. Another significant part of their genetics seem to come from a relatively recent migration from East Asia.

There is some evidence of ancient hominins, including traces of Neanderthal and roughly 0.8 percent Denisovan genes. But the researchers couldn't find any additional hominin mixing ancient enough to have come from a species like the hobbit.

What's Going On?
“Everywhere we look we find admixture, even in populations we thought were different species,” says Amy Goldberg, a population geneticist at Duke University who was not involved in the research. This latest study, she says, is one of the first times in the modern genomic era when researchers haven't found such interbreeding.

She praises the thoroughness of the new analysis, noting that it's possible that hobbit traces could still be there—just not detectable with current methods. But it's also entirely possible, she says, that short stature developed twice through time.

“We think that many strange things happen on islands,” Tucci explains. Exposed to different food availability and often unusual collections—or an overall lack—of predators, island life grows strikingly different than continental creatures. Many become small, a process known as insular dwarfism. That's likely what happened to the mini hippos of Madagascar and the small elephant cousins that once roamed Flores alongside the hobbit. Yet other creatures get big, like Flores' giant rats, which still scramble across the island today. They're “the size of my cat,” Tucci adds.

But Gerrit Van den Bergh of the University of Wollongong cautions against drawing conclusions about the cause of the shrinkage. It's unclear whether insular dwarfism is actually at play for the Rampasasa people, he says. The Rampasasa people are successful farmers, and so scarcity of food—a common proposed driving force for insular dwarfism—may not play a major role in selection.

“Insular dwarfism is itself a bit of a mystery,” Green agrees. “It's one of these things in science that seems like: 'Well, that should [already] be worked out.'” “This study, to me, shows that height has a complex architecture,” adds Sohini Ramachandran, a human population geneticist at Brown University who was not involved in the work. It's still unclear why these short statures evolve, she notes. “There's some more exciting future work to do to incorporate these samples into other studies to understand the genetics of that trait.”

The team is now working to communicate their results to the Rampasasa people. “Bringing back the result is a key part of the research,” says Tucci, who is currently collaborating with an Indonesian illustrator to develop an understandable graphic to present to the village. But there is still much more to do. The research seems to raise more questions than it answers, but it is an tantalizing hint to the life and death of the enigmatic H. floresiensis.

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Homo Floresiensis: The Real-life Hobbits of Indonesia Oct 14, 2019 18:31:12 GMT

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Post by Admin on Oct 14, 2019 18:31:12 GMT

Modelling generations on the island
The Hobbit’s most likely ancestor is Homo erectus, a species more than twice its size in terms of its brain and overall bulk.

Based on the geological history of Flores and the oldest known fossils of Homo floresiensis, it seems the evolution of the new species must have occurred in less than about 300,000 years.

As evolutionary biologists, we are acquainted with the idea that Darwinian evolution is a slow and gradual process that takes place over very long timescales. Could such drastic change in body size happen this fast?

So our interdisciplinary research team developed a computer model to try to answer this basic question.

It’s like a computer game that simulates body size evolution under biologically and ecologically realistic scenarios.

In our model, individuals colonise the island, grow to their adult body size according to how much food is available, give birth to a number of young and die.

The basic rule of the game is that individuals that are closer to the “optimum” body size for the island in that moment will leave more descendants.

Offspring inherit genes for large or small body size.

Generation after generation, new mutations may appear in the population and shift body size toward either higher or lower values.

Occasionally, new individuals might even invade the island and mix with the residents.

Another basic rule is that the initial small population cannot grow above the number the island’s resources might sustain.

Our colleagues, Earth systems scientists Neil Edwards and Phil Holden, used paleoclimatic data to tweak our model.

Hotter and wetter times can support more people on the island, and would influence optimum body size at any given moment.

We started our simulations assuming that large-bodied Homo erectus arrived at the island and then evolved into a smaller species there.

Since we just don’t know the exact numbers our model should crank through, we based them on estimates obtained from current human populations.

Because of this uncertainty, we ran our model thousands of times, each time using a random combination of all the parameters.

Ultimately we were able to build a statistical distribution of how long it took for Homo erectus to become as small as Homo floresiensis.

Last Edit: Oct 14, 2019 19:27:12 GMT by Admin

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Homo Floresiensis: The Real-life Hobbits of Indonesia Oct 14, 2019 19:28:10 GMT

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Post by Admin on Oct 14, 2019 19:28:10 GMT

A new species, in the blink of an evolutionary eye
After running 10,000 simulations, we were surprised to discover that in less than 350 generations, the process was complete.

Thinking in terms of years, assuming a young female delivers a first baby at the average age of 15, that translates to about 10,000 years.

That may seem long for you and me. But from an evolutionary perspective, that’s the blink of an eye – a little more than a thousandth of Homo evolutionary history.

Of course we do not expect that all the features that make Homo floresiensis as unique as it is evolved that fast and at the same time.

Yet, our simulation still shows, 300,000 years is far more than enough time for a new human species to arise.

Our work supports the idea that fast evolution is quite plausible under a realistic set of ecological parameters, and that natural selection may be a powerful force influencing body size on islands. And if Homo floresiensis is indeed a product of the island rule, she shows – yet again – that we humans tend to obey the same overall rules driving evolution in many other mammals.

Last Edit: Oct 15, 2019 18:26:10 GMT by Admin

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Homo Floresiensis: The Real-life Hobbits of Indonesia Oct 15, 2019 18:28:09 GMT

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Post by Admin on Oct 15, 2019 18:28:09 GMT

The genetics of human short stature
Flores Island in Indonesia has a long history of hominin occupation, including by the extinct Homo floresiensis and a more recent settlement by modern humans. Furthermore, Flores has an extant population of pygmy humans, and H. floresiensis exhibited a diminutive adult size relative to other hominins. Tucci et al. examined genetic variation among 32 individuals, including 10 sequenced genomes, from a population of pygmies living close to the cave where H. floresiensis remains were discovered. These individuals exhibit signatures of polygenic selection explaining the short stature and have genomic content from both Neanderthals and Denisovans, but no additional archaic lineages. Thus, restricted height is under selection at this location and has evolved independently at least twice in hominins.

Abstract
Flores Island, Indonesia, was inhabited by the small-bodied hominin species Homo floresiensis, which has an unknown evolutionary relationship to modern humans. This island is also home to an extant human pygmy population. Here we describe genome-scale single-nucleotide polymorphism data and whole-genome sequences from a contemporary human pygmy population living on Flores near the cave where H. floresiensis was found. The genomes of Flores pygmies reveal a complex history of admixture with Denisovans and Neanderthals but no evidence for gene flow with other archaic hominins. Modern individuals bear the signatures of recent positive selection encompassing the FADS (fatty acid desaturase) gene cluster, likely related to diet, and polygenic selection acting on standing variation that contributed to their short-stature phenotype. Thus, multiple independent instances of hominin insular dwarfism occurred on Flores.