The Heterochronic Evolution of Primate CognitiveDevelopment

Jonas LangerPsychology Department, University of California, Berkeley, CA,USAjonas@socrates.berkeley.edu

How did primate cognitive development evolve? To studythe primate evolution of cognitive development my collab-orators and I have focused on the comparative developmentof logicomathematical and physical cognition in two monkeyspecies, New World capuchins (Cebus appela) and Old Worldmacaques (Macaca fascicularis), two great ape species, com-mon chimpanzees (Pan troglodytes) and bonobos (Pan panis-cus), and humans. Logicomathematical cognition is knowl-edge about necessary qualitative (e.g., class) and quantitative(e.g., numeric) relations. By contrast, physical cognition isknowledge about contingent causal, object, spatial, and tem-poral relations.

Our research has discovered primate cognitive univer-sals in these five species’ logicomathematical and physicalknowledge. It has also discovered progressive displacement orheterochrony in the ontogenetic covariation of the cognitiveuniversals shared by these five species. The evolution of pri-mate cognitive universals is marked by diverging ontogeneticonset and offset ages, developmental velocity, discontinuousdevelopmental extent, stage sequencing, and structural orga-nization.

Much of this evolution of primate cognitive developmentcan be illustrated by their comparative development of logicalclassifying and physical causing. I start with the primate cogni-tive universal of logical classifying. With age all five primatespecies develop the ability to classify objects by propertiessuch as form and material (Langer 1980, 1986; Antinucci1989; Spinozzi 1993; Langer et al. 1998; Spinozzi et al.1998, 1999; Spinozzi and Langer 1999). Thus, classifyingis a candidate cognitive developmental universal—a formallysimilar construction of knowledge by all five species. In this,the comparative primate development of classifying operations

that produce qualitative relations such as categorizing identicalobjects together is paradigmatic of our findings.

Presented, for example, with objects from two-formclasses, such as square columns and cylinders, juvenile ca-puchins and macaques construct single categories only (e.g.,put together cylinders only). Bonobo and common chim-panzees’ development progresses from single- to two-categoryclassifying, but no further when presented with three-formclasses. Humans’ development progresses from single- to two-to multiple- to hierarchic-category classifying.

At the same time we have found major divergences inthe comparative primate development of classifying opera-tions. As just noted, the extent of development is minimalin monkeys (i.e., limited to only single-category classifying),progresses to two-category classifying in great apes, and ismaximal in humans (multiple-category classifying and be-yond). In addition, the onset age for the origins of classi-fying by primates is youngest in humans, intermediate ingreat apes, and oldest in monkeys. The velocity at whichclassifying develops is fastest in humans, intermediate ingreat apes, and slowest in monkeys. The stage sequence ofclassificatory development is similar in humans and greatapes. But the sequence is different in monkeys. The offsetage when primates stop developing classificatory cognition isyoungest in monkeys, intermediate in great apes, and oldest inhumans.

Humans’ comparatively precocious onset age, acceleratedvelocity, extended offset age, and consequent augmented aswell as precocial cognitive development concords with theircomparatively extended as well as precocial brain develop-ment. At birth, human log encephalization quotient is alreadylarger than that of other primate species (Deacon 2000). And,human brain maturation extends into adolescence and youngadulthood, a later offset age than for other primate species(Purves 1988; Gibson 1990, 1991; Paus et al. 1999). Humans’prolonged glial cell growth, myelination of axons, synaptoge-nesis, and dendritic growth in the cortex greatly expand theirbrain especially in the neocortex crucial to their comparatively

August 30, 2005; accepted September 7, 2005Biological Theory 1(1) 2006, 41–43. c©2006 Konrad Lorenz Institute for Evolution and Cognition Research 41

The Heterochronic Evolution of Primate Cognitive Development

advanced cognitive development (e.g., Finlay and Darlington1995; Deacon 2000).

Our primate findings on the development of classifyingoperations are paradigmatic of our other findings on the com-parative origins and development of logicomathematical andphysical cognition by primates. So, on the one hand, thesefindings provide measures of formal similarities between thecognitive development of these five primate species. On theother hand, they also provide measures of formal differencesbetween them. Together, these converging formal similaritiescoupled with diverging formal differences between cognitiveontogenies in primate phylogeny are inconsistent with a sim-ple recapitulatory evolutionary account. Instead, the findingsare consistent with an evolutionary theory of organizationalheterochrony in the timing of cognitive development that ismarked by major phylogenetic changes in ontogenetic covari-ation between cognitive features (Langer 1989, 1993, 2000).

Heterochrony provides a heuristic evolutionary theoryabout the possibilities opened up and the constraints on theorigins and development of cognition in primate phylogeny.To get a more complete handle on how heterochrony worksas an evolutionary mechanism, I have therefore also been an-alyzing the comparative structural organization of cognitivedevelopment in these five primate species. Our research isdiscovering striking divergences in developmental sequencingbetween cognitive domains in primates, and therefore in thestructural organization of their cognitive development.

Physical and logicomathematical cognition develop inparallel in human children (Langer 1980, 1985, 1986). Theonset age is the same for both physical and logicomathemat-ical cognition. Their onset is during very early infancy andprobably the neonatal period, and they develop in synchrony.

We find the other extreme in monkeys: almost total asyn-chrony between their development of physical and logicomath-ematical cognition. Since they are out of developmental phasewith each other they are not likely to be open to similar envi-ronmental influences and to each other’s influence. To graspthe significance this has for the ontogeny of cognition it mayhelp to sketch some illustrative findings.

Monkeys develop core physical cognitions before theydevelop core logicomathematical cognitions. To illustrate, ca-puchins develop simple causality, such as using a support asa tool to get a goal object, by age nine months. They developmore advanced causality, such as using a stick as an instru-ment to get a goal object, by age 18–20 months. Thus, causalcognition is well developed by capuchins by the onset of theirlogicomathematical cognition, such as classifying that theyonly begin to do at around age 15 months.

The ontogeny of the great ape’s physical and logico-mathematical cognition comprises partially overlapping de-velopmental trajectories. While already well underway, theirdevelopment of physical cognition is not completed before

the onset of their logicomathematical cognition. Physical andlogicomathematical cognition constitute partially asynchronicdevelopmental trajectories. Therefore these two cognitive do-mains may eventually begin to be partially open to similarenvironmental influences and to each other’s influences, butbeginning relatively late in chimpanzee and bonobo ontogenyas compared to humans.

From the start of human ontogeny, physical andlogicomathematical cognition constitute contemporaneousdevelopmental trajectories that become progressively interde-pendent. Synchronic developmental trajectories permit directinteraction or information flow between cognitive domains.Mutual and reciprocal influence between logicomathematicaland physical cognition is readily achievable since humansdevelop them simultaneously and in parallel.

In primate evolution, the unilinear growth trajectories ofphysical followed by logicomathematical cognition evolvedinto multilinear growth trajectories of physical cognitionat the same time as logicomathematical cognition. The se-quential pattern of physical followed by logicomathematicalcognition in the ontogeny of monkeys became “folded over”and, hence, concurrent trajectories: (a) first to form descendantpartially multilinear cognitive development midway in greatape ontogeny, and (b) eventually to form fully multilinear cog-nitive development from the start in human ontogeny.

The onset age for beginning to develop physical cognitionis roughly the same in all primates studied so far (see Parkerand McKinney 1999 for a recent review). In monkeys the onsetage for logical cognition is retarded such that its developmentoverlaps very little with their development of physical cogni-tion. In great apes the onset age for logicomathematical cog-nition is partially accelerated such that its development partlyoverlaps with the development of their physical cognition. Inhumans the onset age for logicomathematical cognition is ac-celerated to the point that it is contemporaneous with the onsetage of physical cognition.

Phylogenetic displacement in the ontogenetic onset ortiming of one cognitive developmental trajectory relative toanother within the same organism causes a disruption in therepetition, that is, recapitulation of phylogeny in ontogeny (seeGould 1977, McKinney and McNamara 1991, and Mayr 1994on recapitulation and heterochrony). Such heterochronic dis-placement involves a dislocation of the phylogenetic order ofsuccession. It produces a change in the velocity or timing of an-cestral processes. The velocity may be accelerated or retarded.But, importantly, we have seen, the velocity of developinglogicomathematical development is accelerated in humans ascompared to nonhuman primates.

These comparative data on the organization of and se-quencing between cognitive domains are consistent with thehypothesis that heterochrony is a mechanism of the evolu-tion of primate cognition. On this hypothesis, heterochronic

42 Biological Theory 1(1) 2006

Jonas Langer

displacement is a mechanism whereby consecutively develop-ing ancestral cognitive domains were transformed in phylo-genesis into simultaneously developing descendant cognitivedomains in human ontogeny. Heterochrony produced the re-organization of comparatively nonaligned ancestral cognitivedevelopment in monkeys into partly aligned descendant cog-nitive development in great apes and into fully aligned descen-dant cognitive development in human infancy.

This heterochronic reorganization of cognitive devel-opment opened up multiple cascading possibilities for fullinformation flow between logicomathematical (e.g., classifica-tory) and physical (e.g., causal) constructions in human infancy(e.g., making it possible to form a “logic of experimentation”).These cognitive domains are predominantly segregated fromeach other in time and, therefore, in information flow in theearly development of monkeys. They are partially segregatedfrom each other in time and, therefore, in information flow inthe early development of great apes.

The possibilities opened up for further development varyaccordingly and, I would propose, reciprocally constrain the“direction” of progressive cognitive ontogeny in primate phy-logeny. As we have seen, logicomathematical and physicalcognitive development is already quite substantial in mon-keys. However, their asynchronic early cognitive developmenthampers much further progress with age. The partially syn-chronic and relatively advanced early cognitive developmentof great apes multiplies the possibilities for substantial, if stilllimited, further progress with age, of which two-category clas-sifying is representative. Humans’ synchronic and still moreextensive early cognitive ontogeny opens up comparatively un-limited, permanent, and cascading possibilities for further in-tellectual development. On this evolutionary hypothesis aboutthe descent of cognitive development, human cognitive de-velopment is the source of the history of ideas that can betransmitted between generations to construct our unique cul-tural heritage.

Heuristic Conclusion

Our explorations of the evolution of primate development pointto two research directions. The first is generating comprehen-sive comparative primate research on their attendant brain andcognitive development from birth to maturity. The second isgenerating formal analyses of phylogenetic changes in ontoge-netic covariation between cognitive features, thereby modelingthe heterochronic evolution of primate cognitive development.

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