The Seven Sins of Evolutionary Psychology - Konrad Lorenz Institute

Ian Pitchfordappreciation that the foundations of human naturewere ‘solidified’ way before the Pleistocene era. Iwould like to suggest a broader perspective based onempirical and theoretical considerations.In 1935 William KING GREGORY suggested thatreplication of body parts due to genetic mutationhad been a major mechanism in evolution. In 1971this idea was extended by John ALLMAN’s and JonKAAS’ proposal that the evolution of the brain wascharacterised by the replication of cortical areas (AL-LMAN 1999, p40). RILLING’s and INSEL’s comparativeMRI study of the primate neocortex confirms thefinding that the human brain is slightly over threetimes larger than would be expected for a primate ofthe same body size (1999b). However, the data indicatea striking discrepancy between human andpongid brains in the extensive gyrification in theprefrontal cortex of the former, an important findinggiven the role of this region in complex problem-solving(KOECHLIN et al. 1999), and social intelligence(ROWE et al. 2001; SHALLICE 2001; STUSS/GALLUP/ALEXANDER 2001). As RILLING/INSEL (1999b)conclude this departure from allometric trends“suggests selection for increased gyrification in theprefrontal cortex throughout hominid evolution”.The other area noted for significantly more gyrificationthan expected is the seventh coronal slice, aregion incorporating WERNICKE’s area, long implicatedin the production and comprehension of language(1999b). RILLING and INSEL also note that theincrease in human neocortical gray matter is notproportional with the increase in the volume of therest of the brain and that, although the increase inwhite matter outpaces that in grey, this increasefalls well short of that necessary to retain the samelevel of interconnectivity between neurons. Anotherscan of 11 primate species concentrating onthe corpus callosum and anterior commissure demonstratesthat the increase in primate brain size hasresulted in increasingly independent hemispheres(RILLING/INSEL 1999a). Through their work on theinsular cortex of bottlenose dolphins MANGER et al.(1998) have found that although brain sizes varydramatically across animal species, the range ofmodule size is restricted, though the number of corticalareas across species is highly variable (KAAS1993; KAAS/REINER 1999). For additional evidenceon mosaic brain evolution see BARTON/HARVEY(2000) and DE WINTER/OXNARD (2001). These findingsconfirm that brain evolution is characterisedby the independent evolution of brain structureswith anatomical and functional links. Indeed, oneof the most distinctive features of the neocortex isits modular organization (JONES 2000; MOUNTCASTLE1997; ROCKLAND 1998).The existence of a neuronal type found only inthe brains of pongids and hominids is also likely tobe of importance. Using samples of the anterior cingulatecortex (BRODMANN’s area 24) of 28 primatespecies NIMCHINSKY et al. (1999) found a spindleshapedcell in layer Vb specific to humans and greatapes. The anterior cingulate is known to be involvedin response selection (AWH/GEHRING 1999; TURKEN/SWICK 1999), and performance monitoring (CARTERet al. 1998), but also appears to have a number ofdiscrete, functional regions subserving importantaspects of cognition, emotion, and notably vocalization(BUSH/LUU/POSNER 2000). NIMCHINSKY et al.(1999) note that “the emergence of this unique neuronaltype in a neocortical area involved in vocalizationin primates coincides with the evolution as adefinable anatomic structure of the planum temporale,a region that is important for language comprehension.In view of the language comprehensionabilities of great apes, it is therefore possible that severalcortical structures involved in the production ofspecific vocalizations and in communicative skillssustained simultaneous, considerable, adaptivemodifications during brain evolution in hominoids”.In considering neuroevolutionary matters weshould always keep the issue of sexual dimorphismin mind. There are two types of human brain, maleand female, and it is reasonable to expect that thesehave been subject to different selection pressures.For example, women have a higher proportion ofgrey matter to cranial volume, whereas men have ahigher proportion of white matter and cerebrospinalfluid to cranial volume. Women also have a relativelylarger corpus callosum than men. GUR et al.(1999) found that of the top ten performers in a spatialtask, nine were men, and seven of these men hadgreater white matter volumes than any of thewomen in the study. Our large brains may not simplyprovide an excess of plastic neurons capable ofsubserving any function, but may be a solution tothe problem of retaining adequate functioning overa prolonged life span (HUMPHREY 1999), somethingthat could be of particular importance to caregivers.ALLMAN has found that there is a significant correlationbetween brain weight and maximum life-spanin haplorhine primates (ALLMAN/MCLAUGHLIN/HAKEEM 1993), and that the maximum human lifespanis close to what would be expected for a primateof our relative brain size (ALLMAN 1999, p172). ALL-MAN et al. (1998) have also discovered in a variety ofEvolution and Cognition ❘ 42 ❘ 2001, Vol. 7, No. 1