Professor Adrienne Zihlman relaxes into the desk chair, her mouth curves into a wistful smile and eyes light up as she recalls the day her first “fantasy silverback gorilla” died from a freak heart attack. It’s not that she was happy per se that San Francisco Zoo’s prized gorilla, “Bwana”, had met his end, but a male gorilla specimen was just what she had been waiting for her project on comparative ape anatomy. It was Labor Day weekend of 1994 when Zihlman was alerted that Bwana was dying. She immediately started making phone calls and a few hours later was on her way to “save” Bwana’s invaluable flesh from the hazardous waste dumpster. She arrived just in time to negotiate with a California Academy of Sciences representative who was after the bones: “I’ll give you the skeleton after I’ve taken all the flesh off,” parleyed Zihlman. This chance acquisition would ignite a two-decade research venture comparing ape anatomy and locomotor strategies that would challenge some of physical anthropology’s governing paradigms.
Zihlman has been moving and shaking the field of physical anthropology throughout her career. Although best known for her daring works examining the female role in human evolution and groundbreaking research on bipedalism, this new direction is equally radical in its own right.
It may seem intuitive to study both flesh and bone to understand anatomy, but Zihlman’s whole body approach makes her an iconoclast in the field. Anthropology has myopically focused on hominid bones and brains since the field’s beginning, overlooking the other 60-70% of body mass. While fossils recurrently make the cover of Time, and ape intelligence studies abound – note the household names Leakey and Goodall – relatively little is known about the muscles and ligaments, the meat shall we say, of our hominid relatives. In throwing out the flesh and ignoring the habitat context in which apes evolved, researchers are literally left with a skeleton of the available data, perhaps missing valuable insights into still-debated questions about human evolution.
Zihlman pushes physical anthropology to reconsider its procedures and adopt a holistic lens on anatomy that does not focus on single parts or bones, but zooms out to examine the relationships of parts. Her methodology synthesizes measurements of bones, muscles, joints, ligaments, and examines how the entire animal works with its habitat, to see a whole that is greater than the sum of its parts.Zihlman attributes her integrated perspective to graduate school days studying at UC Berkeley under renowned anthropologist, Sherwood Washburn. Washburn too was a big picture thinker, and Zihlman is proud to carry on his visionary tradition.
A self-proclaimed “ambulance chaser”, Zihlman has now dissected five silverback gorillas, four “orangs”, innumerable chimpanzees, and many gibbons for the anatomy project, thanks to patience and relationships with zoos and institutions like the SF Zoo and the Santa Clarita Gibbon Conservation Center. Each dissection involves meticulous calculations and painstaking documentation of each bone, limb, muscle, tendon and most importantly, their proportions and ratios.
She is compiling all this data into a volume that will make her data available to sharper insights into hominid lineage and help field researchers understand how underlying infrastructure informs how each ape can interact with the environment. Zihlman collaborated with anatomist and artist Carol Underwood to make the book both informative and beautiful. It will feature detailed diagrams of each species’ skeleton adjacent to other similar species’ skeletons, skeletons drawn with muscles attached, each ape depicted in various body positions in their habitat, and individual photos of each muscle and perhaps most important, a chapter detailing her methodology so that others in the field can continue in her footsteps.
The fruitfulness of Zihlman’s approach is evident in her preliminary findings, published in a recent paper on gibbon anatomy. It was traditionally thought that there were gibbons and related siamangs. However, recent studies found that there are actually four gibbon genera, each with different number of chromosomes. However, three of the genera are the same size and seemingly indistinguishable from each other. Zihlman compared limb and segment ratios of the four genera and sure enough was able to find clear differences between the musculature proportions and body mass ratios, something impossible to discover with only skeletal data or field observations.
The ingenuity of Zihlman’s anatomy research is not the criticism of physical anthropology’s osteological dependency, but the constructive nature of this criticism. Her new book compiles a wealth of previously unknown anatomical data in a visually stunning fashion, and perhaps most importantly offers instruction for her research methods so that others too can explore the untapped guts of the primate body. In shifting anthropology’s focus from nuts and bolts themselves to how the nuts and bolts of the hominid body fit together and function, Zihlman hopes that her anatomical methods and findings can help physical anthropology make insights and reach conclusions “based on data instead of fantasy.”