Some people argue that humans are merely crazy apes, but the counter-argument, that humans and apes are dramatically different, is not easily dismissed. Truly, it's a question of focus--and the focus often depends on hidden philosophical attitudes. Western religions, for example, abhor the idea that humans are not unique creations of some divine entity, indeed creations in the image of that entity. In the opposing camp are those who focus on the reality of human evolution from an ape lineage, on the extreme similarities between apes and humans in physiology and behavior, and on the solid evidence that apes and humans have diverged as a consequence of only a relatively small number of different genes.
The argument, of course, began in the middle of the 19th century with Darwin's On the Origin of Species, but this is a new era in science and the language of the argument has changed.
So if humans are merely animals, how different are we from other animals?
In this context, let's define "animals" as all living multi-cellular creatures other than humans that are not plants. In recent decades it has become apparent that the cognitive skills of many animals, especially non-human primates, are greater than previously suspected. Part of the problem in research on cognition in animals has been the intrinsic difficulty in communicating with or testing animals, a difficulty that makes the outcome of a cognitive experiment heavily dependent on the ingenuity of the experimental approach.
Another problem is that when investigating the non-human primates, the animals whose cognitive skills are closest to that of humans, one cannot do experiments on large populations because such populations either do not exist or are prohibitively expensive to maintain. The result is that in the area of primate cognitive research reported experiments are often anecdotal, i.e., experiments involving only a few or even a single animal subject.
But anecdotal evidence can often be of great significance and have startling implications: a report, even in a single animal, of important abstract abilities, numeric or conceptual, is worthy of attention, if only because it may destroy old myths and point to new directions in methodology. In 1985, T. Matsuzawa reported experiments with a female chimpanzee that had learned to use Arabic numerals to represent numbers of items. This animal (whose name is "Ai") can count from 0 to 9 items, which she demonstrates by touching the appropriate number on a touch-sensitive monitor. Ai can also order the numbers from 0 to 9 in sequence.
The famous bonobo chimpanzee Kanzi, reared by biopsychologist Sue Savage-Rimbaugh, although unable to speak words, understands spoken English and communicates by punching symbols on a special keyboard.
Ai and Kanzi are not unique, but teaching chimpanzees to communicate with us is not easy and not quickly accomplished even if you know how to do it.
The name "chimpanzee" usually refers to members of a species called Pan troglodytes, animals found in a broad but discontinuous distribution across equatorial Africa. Such are "common chimpanzees" and are distinguished from their close relative the pygmy chimpanzee or bonobo (Pan paniscus), which lives only south of the Congo River in the current-day Democratic Republic of Congo. Genetic similarity as close as that between humans and chimpanzees should lead routinely to classification in the same genus. But adopting that logic would make us all chimpanzees or all chimpanzees members of the genus Homo--an idea that makes many people uncomfortable.
The biologist Linda Vigilant has pointed out that in contrast to what many people believe, chimpanzees and humans are not distinguished by tool use, hunting, or group aggression--both species demonstrate those behaviors. The unique attributes of humans include advanced culture and technology: complex spoken language, art, and sophisticated tool use. We're also uniquely susceptible to malaria, a habitual upright gait, and certain cancers as human-specific features. A handful of genetic or biochemical differences have been identified, but chimps and humans shared a common ancestor only approximately 5 to 7 million years ago, and it's not simple to find genes that hint at selection over such a short time.
Into this debate about similarities and differences between chimpanzees and humans now arrives a new book by Jeremy Taylor, a UK BBC science journalist and film producer. It's an interesting and readable book, particularly since Taylor takes a strong position in the debate. His focus is on differences, but his argument is biological rather than religious or philosophical. He makes three main points:
1) We have been evolving much faster than the chimpanzees. The rate of evolution in the human genome has apparently increased since we and the chimps split from a common ancestor. At least 7 percent of human genes have evidently changed within the past 50,000 years.
2) We humans have apparently domesticated ourselves in exactly the same way that we have cultivated farm animals, dogs, and crop plants from their wild progenitors.
3) Taylor believes that misguided scientists have suggested a closer genetic relationship between humans and chimpanzees in order to build sympathy for an endangered species.
These are strong views. Many people (including myself) may be opposed to Taylor's conclusions, but this is a provocative book that should be read by anyone interested in the debate about similarities and differences between humans and chimpanzees.