The role of humans in the cognitive development of apes revisited
3
Anim Cogn (2004) 7: 213–215 DOI 10.1007/s10071-004-0227-x COMMENTARY Michael Tomasello . Josep Call The role of humans in the cognitive development of apes revisited Received: 5 May 2004 / Revised: 21 May 2004 / Accepted: 17 June 2004 / Published online: 23 July 2004 # Springer-Verlag 2004 Call and Tomasello (1996) reviewed all of the extant literature on ape cognition, with a special eye to comparing the performance of enculturated and non- enculturated apes. The basic finding was that enculturated apes seem to have developed special cognitive skills in two domains: imitation and gestural communication. We outlined four different mechanisms that might possibly give rise to these differences: simple exposure to human life, emulation learning of human actions, explicit training by humans, and being treated by humans as intentional beings. Our conclusion was that being treated as an intentional being is probably key and it “may lead to a fundamental change in the social cognition of apes such that they begin⋯ to view others as intentional agents” (p. 394), and that this may explain the observed differences in imitation and gestural communication. Bering (2004) does not believe that any apes, enculturated or otherwise, understand intentions. His alternative hypothesis for explaining why enculturated apes do some special things is that apes raised by humans come to be “especially attuned to the actions of humans on objects.” Or said another way: “human socialization leads mainly to behavioral change in the form of different problem solving strategies on novel objects.” The cogni- tive skills of apes thus do not change in any fundamental way when they are raised by humans; it is just that apes raised by humans learn to attend to human action in new ways. We do not believe this is a viable hypothesis. First of all, Bering’ s(2004) hypothesis focuses only on the imitation experiments performed by our group (mainly Tomasello et al. 1993; see also Carpenter et al. 1995) and those performed by Bering et al. (2000) and Bjorklund et al. (2002). But the fact is that apes raised by humans behave differently in a number of other ways not involving objects in any direct way. First, apes that have had extensive experience with humans often learn to “point” to things they want and locations they want access to (typically not with an extended index finger). Virtually all of the apes that Call and Tomasello (1996) called enculturated point for humans in one way or another, and the research of Leavens and Hopkins (1999) has documented indicating behavior by captive apes that interact regularly with humans as well. This kind of indicating behavior is most often concerned with food, and involves no manipulation of objects. Moreover, Itakura and Tanaka (1998) and Call et al. (2000; see also Call and Tomasello 1994) have found that the most successful subjects in the so-called object choice experimental paradigm are almost always apes having extensive contact with humans—and the object choice paradigm again concerns communication, not the manipulation of objects. Finally, human-raised apes also outperform other apes in the seeing–begging experimental paradigm in which apes gesture to humans who are either oriented to them or not in various ways (Call and Tomasello 1994; Gómez 1996). Here again objects are involved in only a very indirect way; the human exper- imenter is certainly not manipulating objects. But our original hypothesis is not viable either. This is because of still other recent data—in this case concerned with the cognitive skills of non-enculturated apes. Two recent studies suggest that non-enculturated apes may have some understanding of intentions in others. First, Call and Tomasello (1998) tested apes’ ability to distinguish purposeful from accidental actions. They trained subjects to associate a marker placed on top of one of three opaque buckets with the location of hidden food. On test trials a human then placed the marker on one of the buckets purposefully, but either before or after this he let the marker fall accidentally onto one of the other buckets. The marker was removed at the time of choice, so for test trials apes were faced with a choice of two buckets, one of which had previously been marked in a purposeful way and the other of which had been marked only accidentally. Apes as a group chose the bucket that had been marked in M. Tomasello (*) . J. Call Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany e-mail: [email protected] Tel.: +49-341-9952400 Fax: +49-341-9952119
Transcript of The role of humans in the cognitive development of apes revisited
Anim Cogn (2004) 7: 213–215DOI 10.1007/s10071-004-0227-x
COMMENTARY
Michael Tomasello . Josep Call
The role of humans in the cognitive development of apes revisited
Received: 5 May 2004 / Revised: 21 May 2004 / Accepted: 17 June 2004 / Published online: 23 July 2004# Springer-Verlag 2004
Call and Tomasello (1996) reviewed all of the extantliterature on ape cognition, with a special eye tocomparing the performance of enculturated and non-enculturated apes. The basic finding was that enculturatedapes seem to have developed special cognitive skills intwo domains: imitation and gestural communication. Weoutlined four different mechanisms that might possiblygive rise to these differences: simple exposure to humanlife, emulation learning of human actions, explicit trainingby humans, and being treated by humans as intentionalbeings. Our conclusion was that being treated as anintentional being is probably key and it “may lead to afundamental change in the social cognition of apes suchthat they begin⋯ to view others as intentional agents” (p.394), and that this may explain the observed differences inimitation and gestural communication.
Bering (2004) does not believe that any apes,enculturated or otherwise, understand intentions. Hisalternative hypothesis for explaining why enculturatedapes do some special things is that apes raised by humanscome to be “especially attuned to the actions of humans onobjects.” Or said another way: “human socialization leadsmainly to behavioral change in the form of differentproblem solving strategies on novel objects.” The cogni-tive skills of apes thus do not change in any fundamentalway when they are raised by humans; it is just that apesraised by humans learn to attend to human action in newways.
We do not believe this is a viable hypothesis. First of all,Bering’s (2004) hypothesis focuses only on the imitationexperiments performed by our group (mainly Tomasello etal. 1993; see also Carpenter et al. 1995) and thoseperformed by Bering et al. (2000) and Bjorklund et al.(2002). But the fact is that apes raised by humans behave
differently in a number of other ways not involving objectsin any direct way. First, apes that have had extensiveexperience with humans often learn to “point” to thingsthey want and locations they want access to (typically notwith an extended index finger). Virtually all of the apesthat Call and Tomasello (1996) called enculturated pointfor humans in one way or another, and the research ofLeavens and Hopkins (1999) has documented indicatingbehavior by captive apes that interact regularly withhumans as well. This kind of indicating behavior is mostoften concerned with food, and involves no manipulationof objects. Moreover, Itakura and Tanaka (1998) and Callet al. (2000; see also Call and Tomasello 1994) have foundthat the most successful subjects in the so-called objectchoice experimental paradigm are almost always apeshaving extensive contact with humans—and the objectchoice paradigm again concerns communication, not themanipulation of objects. Finally, human-raised apes alsooutperform other apes in the seeing–begging experimentalparadigm in which apes gesture to humans who are eitheroriented to them or not in various ways (Call andTomasello 1994; Gómez 1996). Here again objects areinvolved in only a very indirect way; the human exper-imenter is certainly not manipulating objects.
But our original hypothesis is not viable either. This isbecause of still other recent data—in this case concernedwith the cognitive skills of non-enculturated apes. Tworecent studies suggest that non-enculturated apes may havesome understanding of intentions in others. First, Call andTomasello (1998) tested apes’ ability to distinguishpurposeful from accidental actions. They trained subjectsto associate a marker placed on top of one of three opaquebuckets with the location of hidden food. On test trials ahuman then placed the marker on one of the bucketspurposefully, but either before or after this he let themarker fall accidentally onto one of the other buckets. Themarker was removed at the time of choice, so for test trialsapes were faced with a choice of two buckets, one ofwhich had previously been marked in a purposeful wayand the other of which had been marked only accidentally.Apes as a group chose the bucket that had been marked in
M. Tomasello (*) . J. CallMax Planck Institute for Evolutionary Anthropology,Deutscher Platz 6,04103 Leipzig, Germanye-mail: [email protected].: +49-341-9952400Fax: +49-341-9952119
a purposeful manner (with the enculturated orangutanChantek clearly outperforming his non-enculturated con-specifics and the chimpanzees). Second, Call et al. (2004)presented chimpanzees with a human who had food in hishands and then behaved in a variety of different waysindicating that he was either unwilling (three conditions)or unable (six conditions) to give them the food.Conditions were matched with one another so that thegeneral behavior of the human, including his lookingactivities, was similar across the various matched un-willing and unable conditions. The main finding was thatchimpanzees were more impatient—banged on the cagemore, left the area sooner—when the human was beingintransigent (unwilling) than when he was making a goodfaith effort (unable), even though they did not actuallyreceive the food in either case.
So our conclusion now is that all apes, not justenculturated ones, understand essential aspects of inten-tional action. In addition, chimpanzees may also knowmore about other psychological states such as visualperception than previously thought. For instance, Hare etal. (2000, 2001) placed a dominant and a subordinateindividual into competition with one another over food—with some food pieces visible to both individuals andsome visible only to the subordinate chimpanzee. Bygoing most often for the piece of food hidden from thedominant’s view, subordinates demonstrated that theyknew what the dominant could and could not see. It shouldbe noted that although Karin-D’Arcy and Povinelli (2003)failed to replicate this finding—a point stressed by Bering—their experimental methods differed in crucial waysfrom the studies of Hare et al. (and we are now preparingfor publication our own successful replication usingdifferent chimpanzees and different experimenters).
Although each of these recent experiments on apeunderstanding of intentions and visual perception may beinterpreted in different ways, we are now convinced by theweight of the evidence that apes that grow up in all kindsof reasonably normal settings come to understand thatothers have goals and so visually monitor their environ-ments in pursuit of their goals (see Tomasello et al. 2003a,b; Povinelli and Vonk 2003; note that we do not claim thatapes understand other mental states such as thoughts andbeliefs—see Tomasello and Call 2004, for a recentreview). This obviously changes the way we view whathappens to apes’ cognitive skills when their ontogenytakes place within a human cultural setting. Although thereare not enough solid data to feel confident about anyhypothesis, our own speculation at this point would besomething like a broadened version of Bering’s—with theproviso that we are talking about apes understandingintentions (whereas he is not). Specifically, we would liketo change our enculturation hypothesis to a somewhatweaker socialization hypothesis. In growing up withhumans who control their world totally and who interactwith them in ways that other apes do not—for instance,attempting to direct attention, comprehending their indi-cating gestures, ordering others what to do—apes acquirea different set of social skills than their wild conspecifics
for interacting with humans. These involve attending tothe intentional actions and referential actions of others notonly in terms of their end results, but also, to some degree,in terms of their composite plans. We cannot be morespecific at this point due to a general dearth of systematiccomparisons among apes with different rearing histories.But Call and Tomasello (1996) identified at least fourdifferent types of rearing histories for apes—within ahuman culture, laboratory-trained, nursery-raised, andmother-raised in captivity; any full account will almostcertainly have to take account of this variability.
Our view is thus that new evidence, since 1996, hasreinforced the case for the existence of systematicdifferences between apes with different rearing historiesbut also for the existence of some unsuspected cognitiveskills in all apes. These additional data have given us adifferent perspective on the question of what kinds ofinfluence humans have on the cognitive development ofapes. Since even non-enculturated apes understand someaspects of intentional actions, it is likely that humanexperience only serves to modify existing social interac-tional and attentional skills—rather than creating newones. We still think the process is extremely interestingand important and we hope that in the future rigorousexperimental methods may be used to try to understandmore about what happens to apes’ cognition when theyinteract extensively over time, from early in ontogeny,with their human cousins.
This is a broader view than Bering’s and, we wouldargue, it relies on a more plausible evolutionary scenario.Bering (2004) argues that “the neurological systemssupporting intentionality and mental state attributionevolved rapidly (perhaps even as a saltation), finding noprecedent in the cognitive hardware of the commonancestor of humans and chimpanzees.” This is possible, ofcourse, but we think it is more likely that somecomponents of human social cognition were present inthe common ancestor of humans and chimpanzees (orother apes), and evolution worked to transform these intosomething new. Rather than viewing social cognition as aunitary phenomenon—something like “theory of mind”that a species either does or does not possess—we think itis more fruitful to turn up the microscope and investigatethe various components of uniquely human social cogni-tion as they have developed phylogenetically andontogenetically.
References
Bering J (2004) A critical review of the enculturation hypothesis: theeffects of human rearing on great ape social cognition. AnimCogn. DOI 10.1007/s10071-004-0210-6
Bering J, Bjorklund DF, Ragan P (2000) Deferred imitation ofobject-related actions in human reared juvenile chimpanzeesand orangutans. Dev Psychobiol 36:218–232
Bjorklund DF, Yunger JL, Bering JM, Ragan P (2002) Thegeneralization of deferred imitation in enculturated chimpan-zees (Pan troglodytes). Anim Cogn 5:49–58
214
Call J, Tomasello M (1994) Production and comprehension ofreferential pointing by orangutans (Pongo pygmaeus). J CompPsychol 108:307–317
Call J, Tomasello M (1996) The effect of humans on the cognitivedevelopment of apes. In: Russon AE, Bard KA, Parker ST (eds)Reaching into thought. Cambridge University Press, New York,pp 371–403
Call J, Tomasello M (1998) Distinguishing intentional fromaccidental actions in orangutans (Pongo pygmaeus), chimpan-zees (Pan troglodytes), and human children (Homo sapiens). JComp Psychol 112:192–206
Call J, Agnetta B, Tomasello M (2000) Social cues that chimpanzeesdo and do not use to find hidden objects. Anim Cogn 3:23–34
Call J, Hare BH, Carpenter M, Tomasello M (2004) ‘Unwilling’versus ‘unable’: chimpanzees’ understanding of intentionalaction. Dev Sci (in press)
Carpenter M, Tomasello M, Savage-Rumbaugh ES (1995) Jointattention and imitative learning in children, chimpanzees, andenculturated chimpanzees. Soc Dev 4:217–237
Gómez JC (1996) Non-human primate theories of (non-humanprimate) minds: some issues concerning the origins of mind-reading. In: Carruthers P, Smith PK (eds) Theories of theoriesof mind, Cambridge University Press, Cambridge, pp 330–343
Hare B, Call J, Agnetta B, Tomasello M (2000) Chimpanzees knowwhat conspecifics do and do not see. Anim Behav 59:771–785
Hare B, Call J, Tomasello M (2001) Do chimpanzees know whatconspecifics know and do not know? Anim Behav 61:139–151
Itakura S, Tanaka M (1998) Use of experimenter-given cues duringobject-choice tasks by chimpanzees (Pan troglodytes), anorangutan (Pongo pygmaeus), and human infants (Homosapiens). J Comp Psychol 112:119–126
Karin-D’Arcy R, Povinelli DJ (2003) Do chimpanzees know whateach other see? A closer look. Int J Comp Psychol 15:21–54
Leavens DA, Hopkins WD (1999) The whole-hand point: thestructure and function of pointing from a comparativeperspective. J Comp Psychol 113:417–425
Povinelli DJ, Vonk J (2003) Chimpanzee minds: suspiciouslyhuman? Trends Cogn Sci 7:157–160
Tomasello M, Call J (2004) Social cognition in chimpanzees. In:Hurley S, Nudds M (eds) Rational animals, Oxford UniversityPress, Oxford (in press)
Tomasello M, Savage-Rumbaugh ES, Kruger AC (1993) Imitativelearning of actions on objects by children, chimpanzees, andenculturated chimpanzees. Child Dev 64:1688–1705
Tomasello M, Call J, Hare B (2003a) Chimpanzees understandpsychological states—the question is which ones and to whatextent. Trends Cogn Sci 7:153–156
Tomasello M, Call J, Hare B (2003b) Chimpanzees versus humans:it’s not that simple. Trends Cogn Sci 7:239–240
215
