Deciding Not to Be a Chimp
The origins of life. The extinction of dinosaurs. Human origins and evolution. These topics, fraught with scientific controversy, fascinate us. Consequently they attract the popular media. However, for any science writer, these topics are difficult. Data changes seasonally, authorities agree on little, and theory changes without notice.
Ann Gibbons tells the story of human origins and evolution by addressing one of its aspects, the search for the earliest human, that critter who, so long ago, decided not to be a chimp.
What makes Gibbons' task so daunting is the speed at which the subject changes. One example she uses will illustrate the problem. If we're going to find the first human, we have to know where to look. Until 17 July 1959, the conventional wisdom placed human origins in Asia. Then, on that date, Mary Leakey discovered Zinjanthropus boisei, a link between Africa's much older Australopithecans and us. In so doing she demonstrated once and for all the African origins of humankind.
Bingo, problem solved. If the 600,000 year old Zinj, as he became known to his friends, wasn't the oldest hominid, he was probably pretty close and anything older would probably be found somewhere close to Olduvai Gorge, or at least in East Africa's Great Rift Valley. That's the story I learned in college in 1964.
It didn't hold up. Potassium-argon dating came along and Zinj suddenly became 1.75 million years old. Then mitochondrial DNA demonstrated that separation of chimps and hominids occurred somewhere between five and seven million years ago. Human paleontologists suddenly had a lot of time to account for. Today, Zinj is seen as an aside, a late offshoot Australopithecine not even in the direct human lineage.
Until recently, there just weren't many three million year old hominid fossils. In the early 1960s they wouldn't have filled a shoebox. Then, Donald Johnson, working in Ethiopia, found spectacular 3.1 million year old hominid remains, Meave Leakey pushed the date back to 4.1 million years, and Tim White and Gen Suwa pushed it back to 4.4 million years. Then in 1995, bones started appearing from some really odd locations, notably around Lake Chad in central Africa, and dates of five, six and even seven million years started being mentioned.
The main focus of Gibbons' book is this most recent, post-1995, period in the search for the first human. To get there, of course, she must review the early history of human paleontology, the period between the 1891 discovery of Java man and Michel Brunet's discovery of a 3.5 million year old fossil he called 'Abel' in central Africa. It's a story that's been told often, though seldom as clearly as in this book.
That early history, full of crusty and romantic characters, is exciting, but nothing compared to what is going on today. There is Tim White of the Middle Awash (Ethiopia) Research Group and a professor at the University of California, Berkeley. He doesn't like showmanship, which is a kind of showmanship itself. There is the Frenchman, Michel Brunet, a professor at the University of Poitiers who has heart trouble and works under impossibly difficult conditions where his tents are frequently buried in wind blown sand. There is the now retired Meave Leakey, wife of the famed Richard Leakey. There is Michael Pickford, the British born geologist who is exploring Kenya's Tugen Hills with his French partner, Brigitte Senut.
These and others are stirring personalities, people devoted to understanding human origins, and serious, some might say contentious, scientists. There is plenty of room for disputation among them. Some is scientific, and some, predictably, is personal. Gibbons handles the personal confrontations with tact and fairness, but she is more interested in how science works, topics ranging from science's instruments to its dialectics.
Right now scientists think the diagnostic human characteristic is bipedalism, walking upright, and the chief contender for the first hominid seems to be Brunet's six-to-seven million year old Sahelanthropus tchadensis from Toros-Menalla, Chad. Agreement is not universal, however. We see bipedalism as the telling characteristic, but ecologically, there's no telling what characteristic our first human ancestors thought made mating with chimp ancestors so unattractive. Could have been the color of their fur. With humans this old there aren't enough matching parts left to permit much comparison between individuals. Is each bone found from a unique species, or are we merely seeing variation among individuals of one species? How do these bones compare with gorilla and chimp remains from the same period? The answer to that question can't even be guessed at since there are no remains of chimp ancestors for comparison. Who'll be the first to find the oldest ancestor of the chimp? How will that scientist even tell a chimp from a hominid?
Neither is Brunet's Sahelanthropus tchadensis likely to be the last word on the subject. New data will emerge, new tools will analyze those data, and new theories will help explain them. In the end, however, we'll probably never get a glimpse of the animal who took the first tentative steps away from the African bush to begin the long journey to the heart of Manhattan.
Gibbons writes about the paleontologists as if she knows them. She does, in fact. She explains their techniques and procedures in language anyone can understand. As the primary writer on human evolution for Science, America's premier scientific journal, she writes with authority about this subject. Her book reads like what you would expect from an award winning science writer of uncommon skill, which is exactly what she is. The book's bibliography is meticulous. The map, the time lines of fossil finds and of human evolution, and her glossary are useful additions as are the brief biographies of the main characters.
Hers is an entirely superlative effort, a must book for anyone interested in human origins, the history and practice of science, or the immensely popular subject of human paleontology.
— 20 April 2006
