The most fascinating scientific result of 2005 – to my mind, at least! – was the sequencing of the chimpanzee genome, reported in the September 1 issue of Nature. (Remember also to read the many accompanying articles on chimp research in the same issue.) Although not the first genome to be sequenced, the chimp genome holds a special importance to research on human cognition and behaviour. The reason for this is the well known fact that chimpanzees are our closest primate relatives. Some 5 to 7 million years ago chimps and the human lineage shared a common ancestor. A comparison of the chimp genome with the human genome will therefore provide invaluable insights into the evolutionary process leading to the creation of homo sapiens. Some interesting finds have already been made. As Elizabeth Culotta and Elisabeth Pennisi write in the Science “breakthrough of year” article that Thomas mentions below
we differ by only about 1% in the nucleotide bases that can be aligned between our two species, and the average protein differs by less than two amino acids. But a surprisingly large chunk of noncoding material is either inserted or deleted in the chimp as compared to the human, bringing the total difference in DNA between our two species to about 4%.
This circumstance feeds a growing suspicion that humans do not so much differ from chimps because of new genes being expressed as because the old genes we share with our chimpanzee brothers and sisters are expressed in a different manner. Various techniques for comparing primate brains (cytoarchitectonics, stereology, imaging) tell much the same story. The human brain is not essentially different from the chimp brain: anatomical areas are more or less arranged in the same manner, it is composed of basically the same cells, and many of the functions it performs are, grosso modo, similar to the functions performed by the chimpanzee brain. There are differences, to be sure. The gene FOXP2, for instance, have mutated twice since the human lineage separated from the chimp lineage. The expression of FOXP2, a trancription factor, is compromised in an English family with a severe speech impediment. Thus, the new variant of foxp2 may have played a role in bringing about human language. Also, Katerina Semendeferi has shown that Brodmann area 10, at the frontal pole of brain, is larger in humans relative to the rest of the brain. Its supragranular layers also appear to form more densely connections with other association areas in the human brain. Yet, it is impossible to say that humans differ from chimps on this or that behaviour which is the product of some new patch of cell tissue, only present in the human brain. We seem to come equipped with a “chimpanzee” brain that have just been modified in a number of subtle ways. Understanding how constitutes one of the great challenges of contemporary science.
On the face of it, chimp behaviour appears to be very different from human behaviour. There are no chimpanzee artists or scientists, for example. No skyscrapers or bridges have been build by chimpanzee engineers and architects. No chimpanzee is blogging from the rainforest of Tanzania about what Jane Goodall is up to these days! For the past 50 years researchers have assembled a long list of putative cognitive cognitive abilities that are unique to humans, and hence contribute to making us different from other primates. However, years of careful observation, and numerous experiments, have, item for item, dismantled this list. Sure, only humans speak, but apes clearly have some semantic capability and are able to refer symbolically to these mental concepts. No chimp will put more than two entities together to form a tool, but they do use sticks to fish for termites, or stones to crack open nuts. Until very recently, most primatologists concurred that only humans are able to read other conspecifics’s minds – that is, that we are the only species to be imbued with a Theory of Mind. It turns out that this is not true. Chimps have ToM as well! Again, tool use, language, and mentalizing, are all clearly different in humans, but they can’t be said to be altogether absent from chimps, if you look carefully at the underlying neurocognitive mechanisms. The lesson to be gained from these behavioural studies, once more, seems to be that humans have inherited a more basic capacity from our common chimp-human ancestor and then have run with it.
A case in point is culture. Culture is very much something we associate with humans, and something that from time to time has appeared on the “unique capacities” list. The “human sciences”, to a large degree, simply define their object of inquiry as culture. (In German the human sciences are often referred to as Kulturwissenschaft; in the US much work go under the name “cultural studies”.) In 1999, however, 9 of the world’s leading primatologists published a report in Nature where they documented that chimps at 7 African communities have developed cultural differences in the use of tool, or social behaviour. The authors define a cultural tradition as behaviour patterns that are customary or habitual in one community, but absent in others, but which cannot be explained by ecological differences. In a recent review of this research, also published in Nature, one of the authors, Andrew Whiten, note that number of cultural traditions observed in chimpanzee communities greatly exceeds those found in other species. In fact, other mammals, fish and birds commonly only have been associated with just one tradition. 19 have been identified in orangutans. But a repertoire of no less than 40 behavioural variants have been observed in chimp communities, so something appear to have changed throughout primate evolution. The critical question of course being: what?
Does such behavioural traditions really amount to the thing we call human culture? Well, we may point to some obvious differences: there are a lot more than 40 traditions around in human communities; human culture is cumulative (i.e., we build on, and sometimes improve upon, other people’s behaviour); and many thinkers would argue that human culture is just a much about values as about behaviour. Still, the formation and transmission of traditions are without doubt part and parcel of human culture as well. Perhaps the real benefit from comparing chimp and human culture will be an improved notion of what just exactly culture is! (Such as this attempt by Richard Byrne and colleagues amply show.)
Now, what could possibly be the neurocognitive mechanisms underlying the primate ability to form and transmit cultural traditions? Stay tuned for part II!
Byrne, R. et al. (2005): Understanding culture across species. Trends in Cognitive Science 8: 341-346.
Chimpanzee Sequencing and Analysis Consortium (2005): Initial sequence of the chimpanzee genome and comparison of with the human genome. Nature 437: 69-87.
Whiten, A. et al. (1999): Cultures in chimpanzees. Nature 399: 682-685.
Whiten, A. (2005): The second inheritance system of chimpanzees and humans. Nature 437: 52-55.