February 25, 2008
The Continuity Wars
by Frans B. M. de Waal
For a long time, we’ve been used to scientists who believe we’re totally unique. They simply don’t see humans as part of the animal kingdom, are uninterested in evolution, and indeed uninterested in any meaningful cross-species comparison. They just react with horror to any hairy creature that looks like them, the way Queen Victoria declared the apes displayed, in 1835, at the London Zoo "frightful, and painfully and disagreeably human."
It is different now. We’re dealing with scientists who believe in evolution, claim an interest in it, and sometimes even have great expertise, yet balk at accepting mental continuity between humans and their closest relatives. Admittedly, most of them have a background in the social sciences, such as anthropology or psychology, not biology, which may explain why they argue that Charles Darwin was actually mistaken on this issue and that the cognitive gap between a human and an ape is in fact so wide that it may exceed that between an ape and a beetle.
A beetle? Have they ever seen a beetle brain next to a chimp’s?
Darwin could not have been clearer, saying in The Descent of Man: “… the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.” The evolutionary framework simply has no room for saltationist arguments. Like Darwin, I am not claiming that humans possess absolutely no unique mental capacities – I am sure they do - but these capacities are merely the tip of the iceberg, and I prefer to look at the whole “berg.”
Except for a few differences at the microscopic level, the human brain is barely distinguishable from the ape brain. Its structure, neurotransmitters, and functional connections are all the same. Even our much-heralded frontal cortex turns out to be about the same size as an ape’s relative to the rest of the brain. Since we don’t assume that the human heart or liver work any differently than those of other animals, why shouldn’t this apply to the stuff between our ears? Yes, the human brain is three times larger, but this only means that it can do more, or do certain things better.
We now seem to have two schools of primate researchers. The “gradualists,” who follow Darwin on both counts (evolution and continuity), and the “exceptionalists,” who follow only half the theory. They propose major mental and behavioral differences, often focusing on just one that they feel explains everything that makes our species unique. Even the major scientific journals are taking sides, with Nature publishing more gradualist papers and Science more exceptionalist ones. Entire research institutes are split, such as two directors at the Leipzig Max-Planck for Evolutionary Anthropology, with one director publicly criticizing another on this issue.
Claims and counter-claims arrive at a pace that must be hard to follow for the outside world. For example, a recent exceptionalist paper on how altruism is sadly absent in the apes, hence must be uniquely human, was soon followed by a gradualist correction about how altruism is alive and well in chimpanzees (see my commentary on both). Or a recent prominent paper about highly developed social learning in chimpanzees was forgotten, and in fact unmentioned, when Science published a report about the limits of chimpanzee social cognition. This prompted our recent commentary in Science - which the journal published four months later - about the best way to compare human and ape cognition.
Our main critique was that if both children and apes are tested by human experimenters, this is unfair to the apes. On the surface, the procedures look identical, but the apes are the only ones facing a species barrier. They obviously don’t relate as well to adult humans as children do. Another difference is that children often sit on or next to their parent during testing, meaning that the parent can give all sort of unintentional clues that assist performance, whereas the apes lack this advantage. In fact, apes have been tested for decades in ways that almost guarantee underperformance.
We do have solutions to this problem. A recent study on dog cognition was conducted in the pet owner’s presence, but with the owner blindfolded. This way, they excluded unwanted influences known as “Clever Hans” effects. Shouldn’t children, too, be tested in a way that cancels parental influence?
I do think there is room for careful human/ape comparisons, and that most of the time (but not always) these will come out in favor of the primate with the larger brain. Humans are different, but not as drastically as claimed. The bigger task that we face is not to assign the gold, silver, and bronze medals of smartness in the animal kingdom, but to see what kind of processes underlie all cognition, both human and animal. Evolutionarily speaking, the more parsimonious assumption is that related species will handle similar problems in similar ways, using the same brain areas, (mirror) neurons, and connectivity.
This is something to keep in mind when the next paper comes along postulating a huge human vs. ape difference. My bet is always on the similarities, and indeed over my lifetime I have seen tons of claimed differences fall by the wayside, but rarely a claimed similarity.
A nice illustration is the work on imitation by Vicky Horner and others. Even though everyone uses the word “aping” for imitation, it was until recently held that apes are actually not good at it. Apes were said to lack “true” imitation based on the fact that, most of the time, they refuse to follow the human example. When we removed the human experimenter from the picture, however, and looked at imitation from ape to ape, all of a sudden they turned out to be excellent, faithful copiers of behavior. So, apes actually do ape!
This won’t deter the exceptionalists, however. They have already begun to turn their attention to the next major difference.
The most amusing one I have ever seen occurred in a Dutch newspaper by a serious philosopher writing about man’s place in nature. He proposed that humans differ from all other animals in that only we go on vacation. A sea lion may lie on the beach, he wrote, but not with the purpose of relaxation. Only we set aside time for this.
Perhaps we should just grant him his little distinction, and not fight it, so that we can finally close this line of argument and move on to more important matters.
Trained as an ethologist and biologist, the Dutch-born Frans B. M. de Waal is C. H. Candler Professor in Psychology and Director of the Living Links Center at Emory University, in Atlanta, Georgia, USA.
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