Thursday, July 5, 2007

Putting a face and form to early humans is both science and art

Putting a face and form to early humans is both science and art


June 23, 2004

San Diego Museum of Man
Paleoartist Bill Munns adds finishing touches to a bust of an Australopithecus boisei, a robust early hominid who preceded modern humans by about 1 million years.
In 1970, Rudolph Zallinger, a former art teacher at Yale University, created one of the most enduring images of human evolution: a transforming sequence of primates moving from a small knuckle-walking ape to an upright, thoroughly modern-looking Cro-Magnon male.

By today's standards, Zallinger's "The March of Progress" is wildly inaccurate and misleading. Human evolution, anthropologists now say, is hardly a simple, linear progression from ape to modern man. And some of the species portrayed by Zallinger, such as the robust Australopithecines, are no longer considered to be direct ancestors of modern humans.

But Zallinger's work was – and remains – indelible because it fulfills a decidedly human need. It fleshes out our predecessors. It puts a face on our past.

To be sure, paleoanthropologists have steadily improved and refined the scientific portrait of our predecessors. Two centuries of fossil finds have added depth and breadth to the human picture, so much so that researchers like Tim White, an paleoanthropologist at UC Berkeley, accurately combined hundreds of skull fragments from different individuals to create a single composite skull of Australopithecus afarensis, a hominid that predates modern humans by a few million years.

But bones don't tell the whole tale.

"Aside from scientists working in the field, most people don't get all that much from looking at fossilized bones," said Ian Tattersall, curator of anthropology at the American Museum of Natural History in New York City. "They want to see how those bones fit together, and what these creatures looked like in life."

So, too, do scientists, who are naturally curious to know whether their dry, data-based interpretations of fossil bones actually translate into prehistoric beings who are both real and possible.

The story of Lucy

On Nov. 30, 1974, anthropologists Donald Johanson and Tom Gray unearthed the 3.18 million-year-old remains of a female hominid in the Hadar region of Ethiopia. They dubbed her Lucy. Forty percent of the skeleton was recovered, the most complete fossil discovery of its kind at that time. Lucy's bones – which go on display outside Ethiopia for the first time in 2006 when they travel to the Houston Museum of Natural Science – told tales, providing the first substantial picture of a species that was not exactly human, but getting there.

Lucy's lower jaw contained an erupted third molar, or wisdom tooth, indicating she was an adult at the time of her death. Her teeth were also slightly worn, though not extensively so.

Extrapolating from a near-complete set of vertebrae (backbones) and an intact leg bone, scientists estimate Lucy was roughly 3½ feet tall.

Curvature of her spine, the angle at which her femur fit into her knee joint, and the robust design of her weight-bearing knees and ankles indicate Lucy was bipedal. She walked upright.

The ends of her bones had fused and her cranial sutures had closed, signaling that Lucy's skeletal development was complete – another indication of adulthood.

Lucy's cause of death has never been conclusively determined. Her bones show no damage from predators or scavengers, save for a single carnivore tooth puncture mark on the top of her left pelvic bone.

A comparatively large pelvic opening to accommodate childbirth indicates Lucy was female.

Which, of course, prompts the question: What exactly did they look like? Answers – at least those based on solid, scientific evidence – are hard to come by, sometimes impossibly so. The fossil record of early humans or hominids – like that of dinosaurs and other prehistoric beasts – is frightfully scant. There are huge gaps in the record, expanses of time and place where fossils either don't exist or have yet to be found.

While later species (such as Homo erectus and Homo neandertalensis) are represented by a comparative abundance of recovered bones – even whole skeletons – earlier hominids like A. afarensis have been characterized by handfuls of boney bits, fossilized fragments of disparate skulls, teeth and bones.

Indeed, the total trove of recovered Australopithecine fossils represents just 0.02 percent to 0.00002 percent of the entire estimated living population of these hominids, who lived roughly 4.2 million to 2 million years ago.

It's not much to work with.

There is an art to the science of reconstructing what early humans looked like, and a science to that art. When Zallinger, who died in 1995, created his "March of Progress," he consulted with the scientific authorities of his day. Modern reconstructionists do no less – and often considerably more – in creating their paleolithic makeovers.

Typically, scientists and artists collaborate quite closely.

"It's a small community," said Tattersall. "Scientists know artists; artists know scientists. When we need help, we know who to call."

Step 1: Bones

"Rather than think of a reconstruction as a single process, you need to think of it in degrees of exactitude, each with its own level of precision," said Bill Munns, a one-time movie makeup artist who has done much reconstructive work for the San Diego Museum of Man.

The skeleton, Munns said, is the most reliably reconstructed part of the effort. Bones not only tell tales, they can be positively gabby:

A fossilized pelvic bone or a surviving skull may indicate gender. Women have wider pelvises (to accommodate giving birth); men usually have more prominent brow ridges, eye sockets and jaws.

Race is sometimes identifiable by specific aspects of the skull, such as the shape and size of the nose cavity or hole.

Joints, bones and teeth are approximate indicators of age. Size is an obvious indicator, but so too is smoothness. Older bones tend to be more polished. Teeth wear down. In children, molars may not have emerged; the space between skull plates is greater, and certain bones in the hands, feet, arms and legs may or may not have completed a time-dependent sequence of growth and fusing.

Body weight can be broadly estimated by bone wear at certain points, such as the hip and knees.

Being the hardest, most resistant material in the body, teeth survive best and longest of fossil matter. They make up about 60 percent of the fossils found. Larger, thicker bones come next, though often in bits and pieces.

Nonetheless, researchers and artists can surmise much. For example, they can compare a piece of fossilized femur or thighbone to other, similar remains or to skeletons of extant, related species to reasonably estimate the femur's complete size and shape.

Prescribed ratios, such as the intermembral ratio, which predicts arm length to leg length, make it possible to calculate the span of missing limbs.

Using such techniques, Munns said, "you could reconstruct a full skeleton with a high degree of accuracy – 90 percent or better."

Quest for learning

This study guide is prepared by the Newspaper In Education Department of the Union-Tribune as an aid for teachers and parents. It is aligned with the California State Reading / Language Arts Framework, and the Mathematics and Science Standards. The questions refer to the article on the appearance of early hominids.

1. Reconstruction is based partly on how human we perceive the hominid to have been. How do you define the term "human"? What are the problems with your definition? What characteristics would separate a human from a nonhuman? Are there any exceptions?

2. The next time you eat chicken, draw the shape of each muscle mass on a drumstick, thigh or leg. When the meat is gone, scrub the bone with soap and water, then examine it. Can you see the muscle attachment sites?

3. Ask your science teacher to let you study some bones from the school's collection without telling you what they are. Wrap the bones in plastic to protect them, then use modeling clay to reconstruct the muscles and skin.

4. Study the work done by forensic artists. What special skills do these people need? How do they produce a picture of a victim from just skeletal remains? How accurate are they?

5. Examine a "family tree" of human evolution. How has the shape of this tree changed during the last fifty years? On what basis is each hominid given a particular place? What would cause scientists to reassign a hominid to a different location?

Such confidence, said Munns, is based upon a sound understanding of human physiology and precedence. "The skeleton is basically a factual framework, governed by engineering and mechanical constraints that are reasonably predictable."

Step 2: Muscles

Reproducing ancient musculature is less certain. "First because we don't have fossil muscles," said Munns, "and second, because muscles are more variant in size. The skeletons of Gov. Schwarzenegger and former Gov. Gray Davis are about the same, but the muscles aren't similar. So if you had a skeleton of a governor, how much muscle would you choose to reconstruct it with?"

To some extent, Munns noted, the areas on bones where muscles attach themselves can provide clues to muscle mass. But the information is most useful only in generally describing a species. Individuals vary quite a bit, and nowhere is that more obvious than in the face, where the attachment points are decidedly less defining.

"Reconstructing musculature is more like 75 percent fact and 25 percent speculation," Munns said.

Step 3: Soft tissues

Certainty declines even more when soft tissues like skin and the subcutaneous fat beneath it are taken into account.

"Now you're at about 50 percent fact, 50 percent speculation," said Munns. "Some people reconstructing hominids love to show their understanding of the musculature by sculpting it, then merely draping a thin veneer of skin over it, so that most of the musculature remains perceptible. That's unnatural because it denies the role of subcutaneous fat and tissue, which smoothes out the muscle contours in real life."

The presence and form of cartilaginous tissue – the material that makes up body parts like the nose and ears – are even tougher to figure. "Nothing about the fossil prepares you to say one particular shape is more likely," said Munns, "so you tend to reference other hominids or primates for ideas. Anything you do here is getting more into 25 percent fact and 75 percent speculation."

And finally, there are questions of skin, hair color and other variables affected by disease, injury or simple individuality.

"Now you're at 100 percent speculation," said Munns. "Anything you do is a guess, and anyone pretending it's not pure guesswork is being pretentious."

Missing links

Rarely, if ever, do anthropologists find complete fossil skeletons of ancient humans. As a result, they must deduce the size and shape of missing bones, followed by reconstruction artists who flesh out their findings, as in these models of the early hominid Lucy, by Bill Munns.

Misplaced ideas

Artists have been doing fossil reconstructions since shortly after the first fossils were found. Early results were mixed, to say the least. The big problem, of course, was the chronic lack of material to work with, but scientists early in the last century were also limited by technology and knowledge. They simply didn't know as much as they know now.

Reconstructions were also greatly influenced by preconceived notions, assumptions and nonscientific considerations. When Charles Dawson announced in 1912 that he had discovered fossilized remains of an ancient being near a quarry in Sussex, fellow Englishmen were thrilled. The "Piltdown Man" was lauded as the missing link between ape and human, possessing a heavy, primitive jaw topped by a skull that appeared notably modern.

Best of all, Piltdown was British.

Numerous subsequent reconstructions reflected that national conceit. A rendering displayed at the 1915 Panama-California Exposition in Balboa Park, for example, portrayed Piltdown Man as the quintessential Englishman on the street, missing only the pipe and tweed cap.

Unfortunately for British pride, Piltdown Man eventually proved to be a hoax. The skull turned out to be just a few hundred years old. The jawbone came from an orangutan. The teeth extracted from ancient elephant, camel and canine remains.

"Piltdown Man was a tailor-made hoax," said Mark Hallett, an Oregon-based paleoartist. "The specimen was constructed to meet the expectations of anthropologists and paleontologists of the time. It was supposed to be the 'missing link,' a perfect blend of ape and human characteristics."

Contemporary reconstructions appear to be less buffeted by biases.

"There's a lot more pressure to be very critical of fossil finds today," continued Hallett. "Researchers must document everything properly, and specimens are heavily investigated. People really go over claims with a fine-tooth comb."

That rigor extends to reconstructions, which Tattersall at the American Museum of Natural History said have improved as the science and technologies have been refined.

"I'm more comfortable with reconstructions now," he said. "If you accept that they are not entirely objective statements, that there's always going to be some degree of guesswork and best estimates, they do a good job of making the past real."

John Gurche, a Denver-based paleoartist, said he tries to be "a purist" who focuses solely on what the fossil evidence says without regard to political or cultural considerations. "It's more meaningful that way. The bones speak on their own terms and the result is not just a little human version of ourselves."

Still, he admits artists can feel occasional pressures to extrapolate one way or another.

"There's a range of opinion on how humanlike Australopithecines were. Some people, for example, want to see the anatomy of their feet look very human. Others don't. I went along with the first group until I got an actual cast of the relevant bones. You can't make a modern foot around those bones. But they're not chimplike either. They're unique to that species."

If fossil evidence says a lot about how early humans were constructed, it's much quieter about what they thought or how they behaved. William H. Calvin in his new book, "A Brief History of the Mind," writes that big brained, modern-bodied Homo sapiens were around 200,000 years ago, but "it wasn't until about 50,000 years ago that they were finally doing things that cause us to say, 'They must have thought a lot like we do.' "

Munns said it's a point well-taken.

"Some of the great embarrassments of modern anthropology and paleontology have come from taking a skeletal fact and building an elaborate behavioral delusion around it."

For example, some depictions of A. afarensis portray a couple walking side by side, the male's arm around the much smaller female's shoulders. It's an emotive moment, but there's no hard, incontrovertible proof that these hominids actually behaved in such ways.

But Gurche notes that responsible artists don't create "things like that without some sort of evidence as a beginning point." As examples, he points to:

Anatomical evidence such as A. afarensis' smaller teeth, which some scientists say may be an indication of social organization and monogamy because hominid males no longer required big canines to help fend of competitors for mates, as modern apes still do.

Physical evidence like the famous footprints at Laetoli, Tanzania, that indicate two individuals walked across a plain of volcanic ash 3.6 million years ago, side by side, stride matching stride.

Thus, Gurche contends, a good reconstruction is a reasonable surmise of a scene that wasn't seen. It's an educated guess based on the best scientific evidence of the moment. When looking at reconstructions, he says, people should keep that in mind.

"A reconstruction can be based on astonishingly meager information, and still be valid and useful," added Munns. "It is simply appropriate to disclose fairly what the evidence was and the factual methods or concepts that guided the reconstruction."

Rose Tyson, curator of physical anthropology at the San Diego Museum of Man, agreed, and offered her own simple test:

"A good reconstruction possesses a certain sense of reality. It looks believable. It doesn't look hokey."

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