Anthropologist Adrienne Zihlman comes across as a real softy. She dresses in soft shades, speaks in a soft voice and emanates a gentleness as she talks about one of her favorite subjects: watching the amaryllis in her garden bloom.
Therefore it comes as something of a shock when she takes you to see her "pride and joy," down the hall from her laboratory at UC Santa Cruz. It is a huge walk-in freezer, stacked floor to ceiling with body parts: arms, hands and heads of gibbons, monkeys, chimpanzees and the ample road kill she picks up from time to time.
She opens a smaller freezer and takes out plastic bags holding, well, meat. "This is leftover muscle from Bwana," she says, referring to one of her favorite (now deceased) gorillas. "We saved [the muscle] because it was an interesting shape."
Back in her office, a trunk-sized glass box swarms with beetles munching on decaying jaws and femurs, cleaning off the last remaining bits of flesh, preparing the bones for study. "Our natural recyclers," she calls them, fondly.
One of her claims to fame is the fact that she's the only person ever to dissect four full-grown gorillas. "Fresh, not pickled," she stresses. "Some people don't realize how important that is." Only fresh tissue stands out in bright reds, yellows and white that makes organs and muscle easy to distinguish.
But then, Zihlman has grown accustomed to shaking people up. Her talent for challenging the established figures and ideas in anthropology has made her a wealth of enemies as well as admirers.
"I've been criticized so much," she says. "As a scientist, you've got to have a thick skin. You have to be able to get as well as you give."
'I've Stirred Up the Pot'
In her 30-year effort to puzzle out how humans got to be the way they are, Zihlman has stepped on some formidable toes, taking on such cherished dogmas as belief in "man the hunter"--the idea that humans first stood on two feet primarily in order to hunt down large animals. She has gone beyond the traditional anthropologist's tool of measuring bones to weighing fat and tissue--quantitative anatomy, she calls it.
Perhaps most controversial, she has been on the forefront of efforts to recognize the role of the female of the human species in what has been known until recently as "the evolution of man."
"Even if people try to dismiss what I've done, it's affected the field," she says. "I've stirred up the pot," she says, "and I'm not finished yet."
The answers Zihlman is seeking are central to physical anthropology: Because walking on two feet seems to be a distinctly human characteristic, just how and why did humans evolve their present bipedal (two-footed) posture?
In part, she tries to piece together the past by looking at clues from the present--for example, studying existing primate species that might be closely related to humankind's earliest ancestors. "To understand how we evolved, you have to understand what we were before we were bipeds," she says.
One of her earliest brushes with fame--and notoriety--was sparked by a proposal she and several colleagues put forth in the British journal Nature in the 1970s, arguing that early humans probably looked a lot like a rare species of pygmy chimp that lived in a corner of Zaire. Zihlman's own observations of living pygmy chimps, as well as skeletons, convinced her that these pint-sized primates carried themselves as might be expected of the earliest protohumans: They moved well on the ground as well as in trees, walked upright more often than other primates and seemed more sociable and brighter than other kinds of chimps. They even mated front-to-front.
Most telling for Zihlman, pygmy chimps are remarkably like early humans in physical proportions, with heavier lower limbs and less bulk in the arms. The lower center of gravity makes them naturally more bipedal than other kinds of apes.
The idea that pygmy chimps might be a "living link" to our earliest history was further supported by molecular analyses of blood proteins and DNA revealing that genes of chimps and humans differ by less than 2%.
Finding such a link is critical for understanding human origins, because it allows researchers to study the lifestyles of these earliest ancestors.
Fellow anthropologists, however, were not supportive. Or as Zihlman puts it, more bluntly, "I got trashed for that. But eventually I got my revenge." These days, the notion that pygmy chimps are living links to early humans is no longer considered a radical idea. "Now everyone is studying pygmy chimps," she says.
In particular, the controversy put her head-to-head with Donald Johanson, discoverer of the famous "Lucy," the most ancient fossil ancestor of humanity that anthropologists can agree on.
Lucy couldn't have been a close descendant of the pygmy chimp, argued Johanson, director of the Institute of Human Origins in Berkeley. For one thing, her fossil teeth were much larger and more robust.
What really fueled the sparks between the two scientists, however, was Johanson's insistence that the male members of Lucy's species, officially known as Australopithecus afarensis, were much bigger than the females. The difference between male and female pygmy chimps is rather small.
The big male/small female scenario put forth by Johanson's school of thinking neatly fit in with then-popular notions about humankind's earliest families: Big, strong males went out to dig up dinner, while small, largely sedentary females hung around the hearth barefoot and pregnant, waiting for hubby to bring home the wildebeest.
Zihlman considers these notions wishful thinking, based on present-day ideas of what a nuclear family should be. Lucy's bones are ambiguous, she says. And the larger bones found at a different site near Lucy's could easily be those of another species. For that matter, she says, Lucy could easily be male. The skeletons simply aren't complete enough to tell.
Zihlman's strongest argument for a close link between pygmy chimps and early humans is an illustration she created that has become a kind of personal logo. Joining the left half of Lucy with the right half of a pygmy chimp, she assembled an almost plausible joint creature. Certainly, the two halves could look like members of the same family tree.
Johanson counters that females of Lucy's family must have been much slighter than males; there simply wasn't enough food to go around to build males big enough to take care of the women and kids and feed big women at the same time. Ergo, women were small.
Zihlman says anthropologists like Johanson are blinded by an unacknowledged bias toward the "man the provider" model of human evolution, which reflects Western ideas about mating and matrimony. Male-female pair bonding has been "completely overrated" as the hallmark of early human social structure, she argues.
"In no human society except America during the 1950s do women stay home and not do anything," she contends. (Zihlman says her own strong pair-bond with her molecular biologist husband is a key source of strength.) Johanson has accused Zihlman, in turn, of shaping her science to fit a feminist agenda. (She says that feminism wasn't even a movement when she first studied pygmy chimps.) But Johanson wields a lot of support. At one international meeting, Zihlman was publicly ridiculed for proposing that the A. afarensis bones could be more than one species.
"Someone stood up and told me that I didn't know what I was talking about," she says, still shaking her head in amazement. "I'm willing to stand up and say I don't agree with people. That pisses people off."
The continuing debate over Lucy and the chimps probably accelerated Zihlman's interest in women's absence from the story of evolution, she says. Survival of the fittest, in evolutionary terms, means survival of those most adept at getting their genes into the next generation, and generations to come. And yet, the sex that bore and nurtured and largely raised the next generations had become a missing piece in the evolutionary picture.
In contrast to the "man the provider" scenario, Zihlman and colleagues suggested that women were equal and active participants in early human societies. Women, in fact, provide much of the food for existing primitive societies like the !Kung of southern Africa. Perhaps it was not the need to bear arms, but rather the need to carry babies and gather roots and fruits that gave our two-footed ancestors an evolutionary edge, she and others suggest. Perhaps tools were developed to dig as well as to kill. Perhaps women chose mates who were friendly and shared food, rather than doling it out.
Zihlman doesn't mind if other scientists don't agree with her. She minds when they won't share the podium. "We didn't [propose these ideas] to be right," she says. "We put it out for discussion. Instead, [other researchers] ignored or dismissed it." One scientist even accused her of favoring chimps as hominid ancestors because their peaceful natures appealed to her feminine sensitivities.
A Meeting of Women Only
Frustrated, in 1990, Zihlman organized a meeting of prominent anthropologists at UC Santa Cruz to discuss female biology and evolution. The catch: No men were invited. Critics fumed. Primatologist Irwin Bernstein of the University of Georgia told Science magazine he was "appalled."
Zihlman doesn't see why anyone was offended. Her critics hadn't been objecting all those years when most scientific meetings were exclusively male, she said. Besides, she didn't set out to exclude anyone, she said. It just turned out that way.
She concedes, however, that she did set out to organize a meeting she herself would want to attend. And she had attended all too many scientific gatherings where male scientists shouted one another down, constantly interrupting and dominating the conversation. "It was very stressful," she said. "I wanted people to be comfortable."
Ultimately, Zihlman doesn't think bones alone will ever tell enough to pin down humanity's first baby steps. "Bones are the holy grail," she says. "And bones are important. But you have to do the soft anatomy, too."
The traditional way to do physical anthropology is to collect lots of bones and "measure them to a fare-thee-well," she said. But looking at an animal's weight distribution can reveal an enormous amount that bones don't tell. For example, a sloth is less than 25% muscle and more than 30% gut. Its slow motion is a direct result of the proportions of body tissues: not much muscle and a whole lot of belly.
Comparing feet also can tell a lot about how they are used. A dog, for example, carries about 1.2% of its weight in its feet. But monkeys, who use their feet for grasping as well as walking, concentrate 2.5% in their feet.
Because the distribution of body mass contains so many clues about behavior and lifestyle, Zihlman dissects just about everything she can get her hands on, carefully weighing and measuring and cataloging. "I love numbers," she says. "I love the quantitative stuff."
Working with fresh tissue is important because different tissues stand out more than if they are preserved. "Muscle is red; fat is yellow; connective tissue is white. When it's pickled, it all blends together."
Dissecting fresh meat means she has to work fast, however--especially when a 380-pound gorilla lands in her laboratory, as one did in 1994 when Bwana died at the San Francisco Zoo. Friends and colleagues flew in from Denver and San Francisco to help, along with willing colleagues and undergraduates. They finished in a week--carefully categorizing every bit of bone, muscle and skin.
It also takes a long time to generate results. Her work on gorillas has been a 15-year investment, and only now does she have enough comparative data to convince other scientists that this kind of detailed dissection produces results that shed light on primate--including human--evolution.
Fat and Fertility
Fortunately, her research doesn't cost much. "I'm a cheap date," she says, adding she needs only the freezer, her scalpels and the costs of shipping animals. She subsidizes most of her research herself. "It's the most important thing to me. I'd rather do that than have a new car."
Recently, she and colleague Robin McFarland did a study on fat in primates that suggests that fat around the hips and thighs is not only natural, but probably beneficial--at least in terms of fertility. McFarland's studies of monkeys revealed that more body fat was correlated with shorter time to conception and more successful pregnancies and nursing. And human females carry much more fat compared to males than the females of other primate species.
Zihlman suggests that the most efficient place to put those increased fat supplies are hips and thighs. "You'd want to put it as close to the center of gravity as possible, so as not to interfere with locomotion."
In some way or other, almost everything Zihlman studies circles back to locomotion--the puzzle of how and why the first humans stood up to walk. Locomotion is central because it's connected with several other distinctly human markers, such as freeing hands to make tools.
"If you really want to understand locomotion, you need to know anatomy," she says. "You need to know how muscles work. You need to know biology, physiology, anthropology, psychology. You need to know evolutionary biology."
Indeed, it's this ability to make broad connections that tends to get Zihlman into trouble, as well as bring her applause. "I've never stayed in one little corner and done it to death," she says.
Her hero is Charles Darwin, the founder of evolution science, whose research interests ranged from the ecology of coral reefs to the domestication of plants, from geology to fossils to barnacles to anthropology. "Darwin was interested in everything," she says. "He was the model. He did it all."
And despite the risks to her reputation, she's happy with the way her career has turned out. To be sure, she jokes that she has published far more articles in the British journal Nature than the U.S. journal Science. "I've never been a member of the [U.S.] club, " she says. "In evolution, there's a party line. And if you want to be in with the in group, you have to interpret it the same way."
But her outsider status has also freed her--and forced her--to innovate. She's currently working on a revision of her "Human Evolution Coloring Book," a textbook now in print for 14 years, that contains many of her ideas. Last year, she raised some money for research by holding a seminar for a dozen Disney animators on gorilla anatomy.
And she's still having fun.
Besides, she says, "I'm lucky to have such a wonderful life. I've got a beautiful garden. My amaryllis are blooming."
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A Lot Like Lucy
Did our earliest ancestors look like pygmy chimps? Anthropologist Adrienne Zihlman of UC Santa Cruz created this comparison of a pygmy chimpanzee with half of "Lucy," our earliest known hominid ancestor, of the species Australopithecus afarensis. The striking similarity, she argues, shows that the pygmy chimp is a prime candidate for a living link to our evolutionary past.