The anatomic pattern and left hemisphere size predominance of the planum temporale, a language area of the human brain, are also present in chimpanzees (Pan troglodytes). The left planum temporale was significantly larger in 94 percent (17 of 18) of chimpanzee brains examined. It is widely accepted that the planum temporale is a key component of Wernicke's receptive language area, which is also implicated in human communication-related disorders such as schizophrenia and in normal variations such as musical talent. However, anatomic hemispheric asymmetry of this cerebrocortical site is clearly not unique to humans, as is currently thought. The evolutionary origin of human language may have been founded on this basal anatomic substrate, which was already lateralized to the left hemisphere in the common ancestor of chimpanzees and humans 8 million years ago.

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The cortical circuits subserving neural processing of human language are localized to the inferior frontal operculum and the posterior perisylvian region. Functional language dominance has been related to anatomical asymmetry of Broca's area and the planum temporale. The evolutionary history of these asymmetric patterns, however, remains obscure. Although testing of hypotheses about the evolution of language areas requires comparison to homologous regions in the brains of our closest living relatives, the great apes, to date little is known about normal interindividual variation of these regions in this group. Here we focus on Brodmann's area 44 in African great apes (Pan troglodytes and Gorilla gorilla). This area corresponds to the pars opercularis of the inferior frontal gyrus (IFG), and has been shown to exhibit both gross and cytoarchitectural asymmetries in humans. We calculated frequencies of sulcal variations and mapped the distribution of cytoarchitectural area 44 to determine whether its boundaries occurred at consistent macrostructural landmarks. A considerable amount of variation was found in the distribution of the inferior frontal sulci among great ape brains. The inferior precentral sulcus in particular was often bifurcated, which made it impossible to determine the posterior boundary of the pars opercularis. In addition, the distribution of Brodmann's area 44 showed very little correspondence to surface anatomy. We conclude that gross morphologic patterns do not offer substantive landmarks for the measurement of Brodmann's area 44 in great apes. Whether or not Broca's area homologue of great apes exhibits humanlike asymmetry can only be resolved through further analyses of microstructural components. Anat Rec Part A 271A: 276 -285, 2003. © 2003 Key words: Broca's area; brain evolution; language; great apes; chimpanzee; gorilla Broca's area, located in the inferior frontal gyrus (IFG) of humans, is a key component of the cortical circuitry that subserves language production. In approximately 95% of humans the left hemisphere is dominant for language (Branche et al., 1964), as demonstrated by functional imaging (Petersen et al., 1988) and cortical stimulation studies (Rasmussen and Milner, 1975;Ojemann, 1991). Whereas numerous studies of gross and microscopic structure have revealed anatomic asymmetries that may underlie this functional dominance in humans, an important unresolved question is whether this asymmetric pattern is evolutionarily novel to humans (autapomorphic) or is shared with our closest living relatives, the great apes (synapomorphic).At the microstructural level, Broca's area is comprised of Brodmann's areas 44 and 45 (Aboitiz and Garcia, 1997).

Experiments on imitation typically evaluate a student's ability to copy some feature of an expert's motor behavior. Here, we describe a type of observational learning in which a student copies a cognitive rule rather than a specific motor action. Two rhesus macaques were trained to respond, in a prescribed order, to different sets of photographs that were displayed on a touch-sensitive monitor. Because the position of the photographs varied randomly from trial to trial, sequences could not be learned by motor imitation. Both monkeys learned new sequences more rapidly after observing an expert execute those sequences than when they had to learn new sequences entirely by trial and error.

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Observations on petalial asymmetry for 190 hominoid endocasts are reported, and their statistical differences assessed. While all taxa of hominoids show asymmetries to various degrees, the patterns or combinations of petalial asymmetries are very different, with fossil hominoids and modern Homo sapiens showing an identical pattern of left-occipital, right-frontal petalias, which contrasts with those found normally in pongids. Of the pongids, Gorilla shows the greater degree of asymmetry in left-occipital petalias. Only modern Homo and hominoids (Australopithecus, Homo erectus, Neandertals) show a distinct left-occipital, right-frontal petalial pattern. Analysis by chi 2 statistics shows the differences to be highly significant. Due to small sample size and incompleteness of endocasts, small-brained hominoids, i.e., Australopithecus, are problematical. To the degree that gross petalial patterns are correlated with cognitive task specialization, we speculate that human cognitive patterns evolved early in hominoid evolution and were related to selection pressures operating on both symbolic and spatiovisual integration, and that these faculties are corroborated in the archeological record.

A few Republicans agreeing with basic climate research is not an environmental victory.

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