Over the past few decades, there has been a lot of research published on 'psychological essentialism', which has been observed cross-culturally in young children. Essentialism is the tendency to think about animals, plants and social categories in terms of hidden 'essences'. The earliest experiments that indicated psychological essentialism in children were by Frank Keil (1989, Concepts, Kinds, and Cognitive Development, MIT Press, Cambridge, MA) who asked preschoolers what would happen if an animal was surgically altered to look like a member of another species. For example, would a raccoon that is surgically modified to look and smell like a skunk actually be a skunk? Young children believed that the creature would still be a raccoon. Three-year-olds and four-year-olds believe that also an apple seed, planted in a flowerpot would still grow out to be an apple tree, or that a cow raised by foster parent pigs would still exhibit normal bovine behavior (Gelman & Wellman, 1991. Insides and essences: Early understandings of the non-obvious. Cognition, 38, 213–244). What is more, children are even more essentialist than adults. For instance, Indian preschoolers believe a Brahmin child remains Brahmin, even when raised by untouchables; Five-year-olds believe that French babies brought up by English-speaking parents will grow up to speak French. Essentialism has been documented in several non-western cultures, indicating that this psychological tendency may be a stable part of human cognition (Gelman 2004, Psychological essentialism in children. Trends in Cognitive Sciences, 8, 404–409).

This raises the question: Is essentialism restricted to humans, or does it also occur in other species? Obviously, the experimental procedures I just discussed all rely on language, so experimental design should be radically adapted to probe psychological essentialism in other animals. Yesterday, I was observing (in an unsystematic way) my cat's behavior (an adult male), and his behavior motivated me to think that essentialism may have its roots in the way animals make concepts.

Let me elaborate. Since he was a young kitten, Leibniz, my cat, has been playing with balls of various sizes and in various materials. Ping pong balls, small rubber balls with bells, soft, fluffy balls, etc. Whenever he is presented with a ball and he is in a playful mood, he will gently tap the ball with his front paw. Occasionally, he sees a ball that is obviously too large to play with. Even then, he will try to tap the ball with his front paw (as he did a moment after the picture was taken) and gives up only after a few tries.

At the recent EHBEA conference held April 6-8 at Saint Andrews, I saw presentations by both Andrew Whiten (a primatologist who specializes on nonhuman cultural traditions, especially in chimpanzees) and Christine Caldwell (who examines cumulative cultural evolution in the lab). It was interesting to see the question of cumulative cultural evolution from these two very diverging perspectives.

It is now generally established that nonhuman animals, including chimpanzees, macaques and a variety of bird species, display a socially transmitted behaviors, which in humans are termed cultures. However, to date the evidence for cumulative cultural evolution in nonhumans remains sporadic. For example, in the case of nut-cracking chimpanzees in the Taï forest, there is little variation in how nuts are being processed, i.e., cracked by means of a hammer and anvil, and whereas some individuals have learned to use auxilliary stones to stabilize the anvil, this innovation has not spread to the entire population. The question is: why not?

Andrew Whiten recently co-authored a study in which chimpanzees were confronted with an optimal and cumulatively built technique for extracting honey from an artificial device. Whereas the individuals learned the simple 'dipping' technique with ease, they did not master the more complex 'probing' technique, which built on elements of the dipping technique they already mastered. The chimpanzees thus got 'stuck' at a simple but suboptimal technique, although control tests showed that the more difficult technique was not beyond their cognitive capacities. Why would this be? Whiten tentatively suggested in the paper that chimpanzees may be 'conservative', unwilling to try a new technique if the one they already knew was good enough.

Another line of reasoning, which has garnered much attention, is that of Tomasello.

There is substantial cultural variation in the prevalence of creationism, i.e., the view that the Bible (or other religious writings) provides a historically accurate account of how living things came into being. In some countries, like Iceland or Japan, the view that species arose through a gradual process that is characterized by random variation, selective retention and modification through descent, is almost universally accepted. By contrast, and to the chagrin of scientists and philosophers of science in the USA, only 40 - 50 % of US citizens accept evolutionary theory. In this respect, the USA only does slightly better than Turkey, which ranks lowest on the list of Miller et al.'s study in Science (2006, vol. 313). Where does this variability come from?

My motivation for posting this blog is simple: I am wondering whether it is possible for humans to ever truly internalize counterintuitive scientific principles like evolutionary theory or Newtonian (let alone Einsteinian) physics.

According to developmental psychologists like Elizabeth Spelke or Susan Carey, and cognitive anthropologists like Pascal Boyer and Dan Sperber, humans are endowed with inference mechanisms that enable them to acquire knowledge of the world (these inference mechanisms are known by several terms, such as core knowledge, conceptual modules or intuitive ontologies). Sometimes these inference mechanisms are at odds with scientific principles. A well-studied example is impetus physics, the view that inanimate objects, in order to be propelled, have to be laden with a force (impetus) by an agent or another object in order to be set in motion. This impetus physics yields a lot of imprecise predictions: for example, over 50% of adults believe that a ball, being launched by a sling, will continue in a curvilinear path, or that a ball dropped by a running person will fall straight down instead of describing a parabolic path. Newtonian physics, in contrast, predicts a parabolic path, a prediction only consistently made by people with a college training in physics (see McCloskey's 1983 review in Scientific American to get an idea).

However, an ingenious experimental procedure by Kohhenikov and Hegarty (2001), Psychonomic Bulletin & Review, 8) shows that even expert physicists are guided by the intuitive impetus physics under some conditions.

Today is 6 December - for those living in Belgium and the Netherlands, Saint Nicholas will come to distribute gifts and candy to young children. Saint Nick has been the predecessor of Santa Claus in the US (as you can still see in his red costume, although the bishop's mitre is replaced by a red bonnet, the horse by a flock of reindeer, the Petes by elves, and all references to Christianity have been discarded). It is remarkable how resilient Saint Nick in spite of the foreign cultural pressure of Santa Claus; he is not likely to go away, even though shops tried to promote Santa Claus fiercely a few years ago.