|
ScienceWeek
ANIMAL BIOLOGY: ON HUMANS AND CHIMPANZEES
The following points are made by Linda Vigilant (Current Biology 2004 14:R369):
1) The name "chimpanzee" usually refers to members of a species designated Pan troglodytes and found in a broad but discontinuous distribution across equatorial Africa. Such "common chimpanzees" 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. But for other taxa, genetic similarity as close as that between humans and chimpanzees leads routinely to classification in the same genus. Adopting that logic would make us all chimpanzees, or all chimpanzees members of the genus Homo.
2) Chimpanzees and humans are not distinguished by tool use, hunting, or coalitionary aggression -- both species are known for those kinds of things. Attributes unique to humans include hallmarks of advanced culture and technology, such as complex spoken language, art, and sophisticated tool use. We can also count susceptibility 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 million years ago, and it is not simple to find genes that hint at selection over such a short time. The list currently includes FOXP2, a gene for a transcription factor that apparently plays a role in developing the ability to produce articulate speech, and ASPM, a gene involved in determining brain size. Humans also have a higher proportion of disrupted olfactory receptor genes --pseudogenes -- suggesting that selection for olfactory abilities may have been reduced in the human lineage.
3) The central idea of the chimpanzee genome project is that comparison of the chimpanzee and human genomes will uncover genetic differences underlying the molecular, morphological, and cultural differences between the two species. The power of such an approach was illustrated by a recent study comparing more than 7000 genes from the chimpanzee to those from humans and mice. Signs of positive selection on the human lineage were shown by genes influencing hearing and those encoding catabolic enzymes that could play a role in adaptation to dietary novelties.
4) Of importance is that the newly completed chimpanzee genome sequence will allow testing of hypotheses about the relationship between genetic and observed species differences. In 1975, Mary-Claire King and Allan Wilson proposed that changes in gene regulation are likely to be more important than changes in the sequences of proteins. Evidence in support of this view came from a recent survey of tissue-specific levels of gene expression in humans, chimpanzees, and other primates, which suggested that the rate of change in expression in the human brain is increased. Gene insertions, deletions, and duplications are also likely to have differentially shaped the human and chimpanzee genomes.(1-3)
References (abridged):
1. Mitani, J.C., Watts, D.P., and Muller, M. (2002). Recent developments in the study of wild chimpanzee behavior. Evolutionary Anthropology 11, 9-25
2. Olson, M.V. and Varki, A. (2003). Sequencing the chimpanzee genome: insights into human evolution and disease. Nat. Rev. Genet. 4, 20-28
3. Tomasello, M., Call, J., and Hare, B. (2003). Chimpanzees understand psychological states- the question is which ones and to what extent. Trends Cogn. Sci. 7, 153-156
Current Biology http://www.current-biology.com
--------------------------------
Related Material:
COGNITIVE SCIENCE: NUMBERS AND COUNTING IN A CHIMPANZEE
Notes by ScienceWeek:
In this context, let us 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 (which is still alive and 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 following points are made by N. Kawai and T. Matsuzawa (Nature 2000 403:39):
1) The author report an investigation of Ai's memory span by testing her skill in numerical tasks. The authors point out that humans can easily memorize strings of codes such as phone numbers and postal codes if they consist of up to 7 items, but above this number of items, humans find memorization more difficult. This "magic number 7" effect, as it is known in human information processing, represents an apparent limit for the number of items that can be handled simultaneously by the human brain.
2) The authors report that the chimpanzee Ai can remember the correct sequence of any 5 numbers selected from the range 0 to 9.
3) The authors relate that in one testing session, after choosing the first correct number in a sequence (all other numbers still masked), "a fight broke out among a group of chimpanzees outside the room, accompanied by loud screaming. Ai abandoned her task and paid attention to the fight for about 20 seconds, after which she returned to the screen and completed the trial without error."
4) The authors conclude: "Ai's performance shows that chimpanzees can remember the sequence of at least 5 numbers, the same as (or even more than) preschool children. Our study and others demonstrate the rudimentary form of numerical competence in non-human primates."
Nature http://www.nature.com/nature
--------------------------------
ON CHIMPANZEES
The following points are made by Craig Stanford (citation below):
1) Evolutionary scientists are therapists for the human species. People go to therapy to explore what molded them into who they are today. That desire, writ large, is exactly what the study of human origins is all about. A word of warning... Both lay [people] and scientists misread evolution's signature easily and often. Chimpanzees are not evolutionary challenged people, and people did not evolve from gorillas. They and we share a common ancestor in the nearly invisible past, a past that we try to reconstruct in hopes of catching a sidelong glimpse of that chimerical great grandparent. There are amazing similarities between us today, but also profound differences.
2) While they may look like hirsute, sloped-foreheaded, primitive humans, chimpanzees evolved for some 5 million years after their ancestors diverged from our own. I offer a cautionary shout to all those seeking to extrapolate from apes to humans and vice versa: the great apes are highly evolved in their own right. They inform us of the range of paths taken by our ancestors long ago. This gives us an extraordinarily richer view of humanity than we could have otherwise, but it can also deceive us if we are not careful. At every turn, [we] should remember that humans, chimpanzees, gorillas, bonobos, orangutans and all other higher primates evolved for equally unique reasons. If we are going to understand the meaning of the term "human nature", we must get to the heart of what apes can and cannot tell us about our own cognitive abilities and behavioral tendencies.
3) No claim in science is at once more banal and more profound than that of human uniqueness. Explaining human uniqueness is what anthropologists do for a living. At the same time, primatologists are fond of asserting that apes are more like people than people like to admit. Somewhere between these two claims is evidence of the shared and separate ancestry of humans and their genetic kin.
Adapted from: Craig Stanford: Significant Others: The Ape-Human Continuum and the Quest for Human Nature. Basic Books, New York 2001, p.xv. [The author is Associate Professor of Anthropology at the University of Southern California and Director of the Bwindi-Impenetrable Great Ape Project, Uganda.] More information at: http://www.amazon.com/exec/obidos/ASIN/0465081711/scienceweek
ScienceWeek http://scienceweek.com
|