Evolution’s Mystery Woman

All hail Flo, the diminutive belle of the evolutionary ball. She made a flashy entrance in 2004 using the species name Homo floresiensis, given to her by her discoverers. Flashbulbs popped when the scientists announced the results of their analysis of Flo’s partial skeleton and the assorted bones of other individuals uncovered on the Indonesian island of Flores.

The shape and size of the fossils showed that they came from little cousins of humankind, the team concluded. The island individuals, who lived between 100,000 and 12,000 years ago, stood about 3 feet, 3 inches tall and possessed chimpanzee-size brains.

Flo’s discoverers, led by anthropologist Peter Brown and archaeologist Michael J. Morwood, both of the University of New England in Armidale, Australia, described their fossil gal as being considerably shorter than members of modern pygmy groups, blessed with incredibly strong legs, and a member of a now-extinct Homo species that had spent tens of thousands of years developing its own toolmaking tradition on Flores (SN: 10/30/04, p. 275: Evolutionary Shrinkage: Stone Age Homo find offers small surprise).

Anthropologists largely greeted Flo as a member of a new species of human ancestor. She seemingly provided the first evidence that, like many other animals, the Homo lineage had evolved small island-dwelling forms.

But after being welcomed to the scientists’ evolutionary shindig, Flo continued to make a scene. The fossil islander triggered an unusually vitriolic scientific dispute within months of her discovery. Debate over whether she represents a previously unknown species reached a fever pitch with the publication of a new analysis of the Flores fossils in the Sept. 5 Proceedings of the National Academy of Sciences.

That report concludes that Flo was a pygmy Homo sapiens with a stature about 7 inches taller than previously estimated. What’s more, Flo displays skull and limb abnormalities that resulted from a still-enigmatic, genetic growth disorder, say anthropologist Teuku Jacob of Gadjah Mada University Faculty of Medicine in Yogyakarta, Indonesia, and his coworkers.

These scientists hold that in her prime, Flo tottered on malformed legs or may even have been paralyzed. Some of her fellow Flores folk inherited the growth disorder, the scientists suggest. Still, physically capable members of Flo’s kind fashioned stone tools that could have been made only by anatomically modern people, Jacob’s team asserts.

With such arguments, Flo’s evolutionary status has gotten fuzzier, remarks Susan C. Antón of New York University. It’s tough to delineate precisely where one hominid fossil species ends and another begins, she notes. Longstanding debates over the number of species in the human evolutionary family attest to that difficulty.

“It’s a bit like our Pluto,” Antón says, referring to astronomers’ dustup over how to define planets.

To make matters worse, the Flores finds so far include only one skull and two lower-jaw bones, along with scattered lower-body remains from a handful of individuals. That’s precious little material with which to re-create an ancient population.

Specious species

If you want to look up Flo’s flesh-and-blood descendants while visiting Flores today, just look down, says anthropologist Robert B. Eckhardt of Pennsylvania State University in University Park, a coauthor of Jacob’s new paper. According to Eckhardt, Flo’s modern offspring, the Rampassasa pygmies, live close to Liang Bua Cave, the site of the H. floresiensis discoveries.

These small folk, ranging in height from 4 to 4.5 feet and having brains about standard size for modern humans, possess skeletal features originally described by Brown’s team as unique to Flo’s kind, Eckhardt asserts. For instance, many Rampassasa display receding chins and cheek teeth positioned at an unusual angle.

Overall, 140 skull and tooth features of the Flores fossils also appear in the Rampassasa and other native inhabitants of Australia and Melanesia, Eckhardt and his colleagues hold. They say that Brown’s group erred by comparing their fossil finds mainly with European H. sapiens skeletons.

To compound this problem, Flo’s discoverers used a mathematical formula for estimating stature that shortchanged her height, Eckhardt contends. Flo, also referred to as LB1, stood an inch or two shy of 4 feet, according to his team’s adjusted calculations.

This revised height gives a brain-to-height-ratio that suggests that Flo suffered from an as-yet unspecified growth disorder that included microcephaly, a genetic condition that results in an unusually small head and brain.

Evidence of facial asymmetry strengthens the argument that Flo suffered from a growth disorder, Eckhardt adds. Composite photographs of her facial bones that combine an image of either the left or right side and its mirror image look much different than an unmanipulated photo does. These disparities reveal more pronounced facial-feature imbalances than have been observed in typical modern people, his team reports.

Using a scanning device, Eckhardt and his coworkers found that Flo’s limb bones, although large in diameter, contain unusually thin outer layers of bone, a sign of developmental trouble.

Another finding suggests that she had great difficulty in moving or that she suffered from paralysis, says study coauthor Maciej Henneberg of the University of Adelaide Medical School in Australia. Muscle-attachment sites on Flo’s arm and leg bones show only faint marks, a sign of limited movement throughout her life, since these sites become more prominent with greater muscle use.

A limited ability to twist her upper arm, gleaned from the team’s analysis of Flo’s fossilized arms and shoulders, also underscores her movement difficulties.

Flo “is not a normal member of a new species, but an abnormal member of our own,” Eckhardt says.

Developing doubts

Some anthropologists see the new report from Jacob’s group as a confirmation of their suspicions—largely stimulated by the modern-looking stone tools found with the Flores fossil—that the bones come from Stone Age people, not a new species of human ancestors. “There is genuine cause for concern about the widely popularized scenario of Homo floresiensis,” remarks Robert D. Martin of the Field Museum in Chicago. Jacob’s investigation shows that some modern people in Indonesia possess Flo’s supposedly unique skeletal features, Martin says.

Determining whether Flo had developmental abnormalities will require studies to identify similarities and differences between her limb and torso bones and those of modern adults with microcephaly. Nonetheless, Flo’s brain case strongly resembles that of a short person with microcephaly, Martin and his colleagues conclude in the November Anatomical Record.

The team examined computer-generated reproductions based on measurements of the inner walls of braincases from Flo and two present-day adults with microcephaly, one from Africa and the other from India. The scientists then reconstructed the brain’s surface for each specimen. The three individuals display similar neural contours, the researchers say.

Their report counters earlier findings by a team led by Dean Falk of Florida State University in Tallahassee. Falk’s investigation, using the same method, portrayed Flo’s brain as shaped differently from the brains of modern humans, including the brain of a 10-year-old boy from Germany who had microcephaly (SN: 3/12/05, p. 173: Available to subscribers at Inside view of our wee, ancient cousins).

Anthropologist Erik Trinkaus of Washington University in St. Louis is struck by Flo’s similarities to H. sapiens. For instance, bony protrusions that shore up her lower jaw appear in a modern human skull from Eastern Europe that is more than 100,000 years old, Trinkaus says. Brown’s team had previously cited these protrusions as a unique feature of the Flores fossils.

Flo’s upper-leg bones display much thinner walls than do any comparable bones from previously identified Stone Age individuals, Trinkaus says. “It reminds me of [modern] cases of long-term limb paralysis,” he remarks.

It’s not clear whether such characteristics say more about Flo’s unique growth pattern or her species identity, in his view. “Whatever these Flores fossils are, let’s sort out their biology before talking about their evolutionary status,” Trinkaus says.

Inspired by that idea, evolutionary biologist Gary D. Richards of the University of California, Berkeley reviewed genetic and biological factors that contribute to microcephaly and short stature in people today. Mutations of one gene or a few genes that influence growth hormones in H. sapiens could have yielded an individual such as Flo, Richards concludes in an article published in the November Journal of Evolutionary Biology.

Unlike Jacob and his coworkers, Richards suspects that Flo had no developmental problems such as microcephaly. In his view, she was a typical member of a pygmy H. sapiens group.

Genetically induced reductions of brain and body size show up in substantial minorities of people living in small, isolated populations, Richards says. These changes yield survival-enhancing declines in energy needs with only a minimal loss of thinking skills, he notes.

Individuals in current pygmy populations typically develop “primitive-looking” skeletal features, much like those described for Flo, simply as a result of having small bodies, Richards adds. For Flo and perhaps some of her peers, though, genetically curtailed brain growth might have been more pronounced than that occurring in pygmies today, he contends.

Go with flo

One of the co-discoverers of the Flores fossils finds it difficult to contain his contempt for the new paper from Jacob and his colleagues. Brown brands their analysis “a complete crock.”

Jacob’s group ignores the unique anatomy of H. floresiensis, Brown asserts, such as a thick-boned lower jaw that recalls those of 3-to-4-million-year-old human ancestors in Africa rather than modern human jaws.

The new study erroneously argues that people living on Flores today sometimes lack distinct chins, as Flo’s kind does, Brown adds. Projecting teeth can disguise the presence of a chin on Rampassasa individuals, but “all modern humans, including microcephalics, have one,” he holds.

Further analysis also supports the notion that the shape of Flo’s brain and of the brains of microcephalic people differ substantially, says Falk. She and her coworkers have recently extended their earlier work. They’ve compared computerized braincase reproductions for Flo, 9 people with microcephaly and growth retardation, and 10 regular-size adults. Members of the modern groups came from various parts of the world.

First, Falk says, her team identified substantial shape disparities between the brains of modern folks with and without microcephaly.

Next, the researchers considered a brain reconstruction from a 3 1/2-foot-tall woman with dwarfism, a genetic condition that causes short stature but not an unusually small brain. On a measure of brain shape, Flo and the regular-size adults looked alike, as did the woman with dwarfism and adults with microcephaly.

These results support the notion that Flo’s brain came from an individual free of developmental problems, Falk concludes. Still, she says, Flo possessed enough unusual neural characteristics to uphold her membership in a separate Homo species.

When Australian researchers not connected to Brown’s team compared Flo’s skull with skulls of several modern people and of two fossil individuals with microcephaly, they came to the same conclusion (SN: 7/15/06, p. 37: Available to subscribers at Little Ancestor, Big Debate: Tiny islanders’ identity sparks dispute).

Such findings are persuasive to anthropologist Bernard Wood of George Washington University in Washington, D.C. Much asymmetry in Flo’s skull occurred not during development but after her remains became encased in soil that shifted over time and reshaped the bone, Wood argues.

Out on a limb

Scientific defenders of H. floresiensis have also stepped forward with analyses of Flo’s arms and legs. In presentations at the Paleoanthropology Society’s annual meeting in San Juan, Puerto Rico, last April, Susan G. Larson and William L. Jungers, both of the State University of New York at Stony Brook, described Flo as a healthy H. floresiensis with some unusual limb features.

Larson reported that Flo’s kind possessed substantially shorter collarbones, relative to arm length, than any modern human has. This trait would have pulled the shoulders in and close to the head.

The leg strength of Flo and her peers was “in another universe,” Jungers reported (SN: 5/13/06, p. 302: Available to subscribers at Ancient islanders get a leg up). In build and body size, which he estimates at 55 to 75 pounds, Flo resembles Lucy, the 3.2-million-year-old Australopithecus afarensis skeleton from eastern Africa, Jungers says.

Jungers rejects the new portrait of Flo as a developmentally disabled human. In his measurements, the specimen shows normal outer-bone thickness, not the thin walls reported by Jacob’s group.

Moreover, Jungers contends, marks made by muscles on bone, or the lack of marks, implies nothing about an individual’s mobility. He cites animal studies showing that even intensive exercise doesn’t alter the appearance of spots where muscle attaches to bone. He also emphasizes that Flo’s limb proportions and estimated height don’t appear in any known human population, even the smallest pygmies.

Jacob and his colleagues reject these arguments. For example, they regard Jungers’ measurements and his estimate of Flo’s height as inaccurate.

Another scientific standoff concerns Stone Age tools found at the Liang Bua Cave and at sites dated between 840,000 and 700,000 years old in the nearby Soa Basin (SN: 6/3/06, p. 341: Available to subscribers at Stones of Contention: Tiny Homo species tied to ancient tool tradition). Flo’s discoverers assert that similarities among these artifacts show that H. floresiensis carried on a toolmaking tradition passed down for countless generations by its island forebears.

Critics, such as Martin, argue that only individuals with human-size brains could have fashioned tools as complex as those found at Liang Bua. They suspect that the Soa Basin implements are much younger than 700,000 years.

Who’s that lady?

It’s hard to know when the clouds will part and Flo’s true evolutionary identity will shine through. To make matters worse, Flo’s discoverers say that Jacob and his coworkers studied the Liang Bua fossils after furtively borrowing the bones without first gaining permission to do so from the Indonesian National Center for Archaeology, breaking a written agreement between that body and the University of New England.

Jacob didn’t answer a request to respond to this accusation.

Better tests of the competing views of the Flores fossils will come with further fossil discoveries on the island and with extraction of DNA from Flo’s bones, says anthropologist Tim D. White of the University of California, Berkeley.

Like any mystery woman, Flo watches impassively as scientific suitors slug it out for the right to give her a lasting name.