Left Occipital-Right Frontal Petalia Torque Asymmetry

Humans evolved a distinctive pattern of left-occipital right-frontal petalias. Petalias are a type of cerebral asymmetry that can be observed as the greater protrusion of one hemisphere beyond the opposite hemisphere in modern human brains. The most typical configuration in modern humans is for the combination of a right frontal lobe petalia with a left occipital lobe petalia. Some authors have argued that this petalia torque pattern is unique to modern humans and can be linked to the evolution of language abilities. Fossil evidence attributed to Homo erectus, however, suggests that endocasts of at least some earlier hominin species show similar asymmetrical cerebral petalias (De La Coste Lareymondie and Holloway, 1982). Recent studies by W.D. Hopkins and colleagues, furthermore, using measurements of MRI scans may show left-occipital and right-frontal petalias in chimpanzees (Hopkins and Marino, 2000; Hopkins et al., 2008). There is no evidence of the left-right petalia torque from any other primate species outside the great apes.