Laterality and Human Speciation
Laterality and Human Speciation
This chapter describes the relevance of cerebral asymmetry. Although cerebral asymmetries abound in non-human animals, there are still reasons to suppose that there may have been a single-gene mutation producing a ‘dextral’ (D) allele, which created a strong bias toward right-handedness and left-cerebral dominance for language at some point in hominid evolution. The alternative ‘chance’ (C) allele is presumed directionally neutral, although there may be other influences producing weak population manual and cerebral asymmetries in the absence of the D allele. The discussion argues that language evolved from manual gestures, and the D allele may have served to guarantee manual and vocal control in the same (left) hemisphere in the majority of humans. The ‘speciation event’ that distinguished Homo sapiens from other large-brained hominids might be as witch from a predominantly gestural to a vocal form of language.
Keywords: cerebral asymmetry, left-cerebral dominance, hominid evolution, Homo sapiens, manual gesture, dextral allele
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