Brodmann's area 44 delineates part of Broca's area within the inferior frontal gyrus of the human brain and is a critical region for speech production 1,2 , being larger in the left hemisphere than in the right 1-4 -an asymmetry that has been correlated with language dominance 2,3 . Here we show that there is a similar asymmetry in this area, also with left-hemisphere dominance, in three great ape species (Pan troglodytes, Pan paniscus and Gorilla gorilla). Our findings suggest that the neuroanatomical substrates for left-hemisphere dominance in speech production were evident at least five million years ago and are not unique to hominid evolution.To our knowledge, no one has assessed whether there is any consistent left-right anatomical asymmetry in the inferior frontal gyrus (IFG) of any non-human primate. This is surprising because it is known from cytoarchitectonic and electrical stimulation studies that many nonhuman primates, including the great apes 5,6 , possess a homologue of area 44. We have therefore investigated whether homologous neuro-anatomical asymmetries are present in area 44 in great apes.From magnetic resonance images (MRI) obtained from 20 chimpanzees (P. troglodytes), 5 bonobos (P. paniscus) and 2 gorillas (G. gorilla; Fig. 1a), we found that area 44 in these species shows a pattern of morphological asymmetry that has left-hemisphere surface-area predominance similar to the homologous cortical area of humans (mean left, 127.7 mm 2 ±8.1 s.e.; mean right, 104.2 mm 2 ±6.1 s.e.; F(1,25) = 7.45, P=0.011; see supplementary information for details of the statistical analysis, and see Fig. 1b for individual asymmetry measures). In humans, this region is part of Broca's area, a key anatomical substrate for speech functions, particularly in motor aspects of speech such as articulation and fluency 2,7 .The part possession by great apes of a homologue of Broca's area is puzzling, particularly considering the discrepancy between sophisticated human speech and the primitive vocalizations of great apes. This may be explained by the contribution that gestures have made to the evolution of human language and speech 8 . In monkeys, the so-called 'mirror neurons' in area 44 seem to subserve the imitation of hand grasping and manipulation, and this neural system may have been specialized initially for gestural and later for vocal communication 9 . In captive great apes, manual gestures are both referential and intentional 10,11 , and are preferentially produced by the right hand (which is controlled by the left hemisphere). This right-hand bias is consistently greater when gesturing is accompanied by vocalization 10 .From an evolutionary standpoint, therefore, asymmetry in area 44 may be associated with the production of gestures accompanied by vocalizations in great apes, an ability that eventually Supplementary information accompanies this communication on Nature's website (www.nature.com).

The neurobiology of hand preferences in nonhuman primates is poorly understood. In this study, the authors report the first evidence of an association between hand preference and precentral gyrus-morphology in chimpanzees (Pan troglodytes). Hand preferences did not significantly correlate with other asymmetric brain regions associated with language functions in humans including the planum temporale and frontal operculum. The overall results suggest that homologous regions of the motor cortex control hand preferences in humans and apes and that these functions evolved independently of left-hemisphere specialization for language and speech.

We investigated turning responses in 16 species of fish faced with a vertical-bar barrier through which a learned dummy predator was visible. Ten of these species showed a consistent lateral bias to turn preferentially to the right or to the left. Species belonging to the same family showed similar directions of lateral biases. We performed an independent test of shoaling tendency and found that all gregarious species showed population lateralisation, whereas only 40% of the non-gregarious species did so. The results provide some support to the Rogers (1989) hypothesis that population lateralisation might have been developed in relation to the need to maintain coordination among individuals in behaviours associated with social life.

We investigated turning responses in 16 species of fish faced with a vertical-bar barrier through which a learned dummy predator was visible. Ten of these species showed a consistent lateral bias to turn preferentially to the right or to the left. Species belonging to the same family showed similar directions of lateral biases. We performed an independent test of shoaling tendency and found that all gregarious species showed population lateralisation, whereas only 40% of the nongregarious species did so. The results provide some support to the Rogers (1989) hypothesis that population lateralisation might have been developed in relation to the need to maintain coordination among individuals in behaviours associated with social life.