The genetics and evolution of handedness.

Abstract

At some point in hominid evolution, a mutation may have produced a "dextral" (D) allele, strongly biasing handedness in favor of the right hand and control of speech toward the left cerebral hemisphere. An alternative (chance [C]) allele is presumed directionally neutral, although there are probably other genes that influence asymmetries and that may create a weak bias toward right-handedness (and other asymmetries). Simulations show that the D allele could have spread quite quickly through a population, given even a minuscule advantage of CD heterozygotes over CC and DD homozygotes in terms of reproductive fitness. This heterozygotic advantage would also explain the apparent stability in the relative proportions of left-handers and right-handers. This putative, uniquely human allele may have emerged with the evolution of Homo sapiens in Africa some 150,000 to 200,000 years ago.

Fitting objects into holes: On the development of spatial cognition skills.

“…For right-handed people, hand control is better developed in the left hemisphere, whereas the right hemisphere is dominant for left-handers. Almost 90% of the population is right-handed (Bayley 1969;Corballis 1991;Hepper, Shahidullah et al 1991;Corballis 1997). That is in agreement with the results of Study I, which show that 80% of the children predominantly used the right hand.…”

Heritability of hand preference in chimpanzees (Pan troglodytes): Evidence from a partial interspecies cross-fostering study.

“…The pervasiveness of human right-handedness has led to numerous debates about the mechanisms involved in the expression of hand preference (B. Hopkins & Ronnqvist, 1998). Both genetic models (Annett, 1985;Corballis, 1997;Laland, Kumm, Van Horn, & Feldman, 1995;McManus, 1985;Yeo & Gangestad, 1993) and environmental models (Collins, 1985;Provins, 1997) have been proposed to explain the origin of human hand preference. The principal data in support of a genetic basis for hand preference are that it runs in families (Curt, De Agostini, Maccario, & Dellatolas, 1995;Laland et al, 1995;McGee & Cozad, 1980;McManus & Bryden, 1992) and that offspring typically exhibit patterns of hand preference more similar to their biological parents compared with offspring who have been adopted or raised by stepparents (Carter-Saltzman, 1980;Hicks & Kinsbourne, 1976).…”

The evolution and genetics of cerebral asymmetry

“…Further evidence comes from a study showing a higher concordance of handedness in siblings of the same sex than in opposite-sex siblings, as expected from linkage to homologous X-Y loci (Corballis et al 1996), but the effect was weak. One argument against this theory is that polymorphisms are unstable on the Y chromosome (Corballis 1997), yet variations in handedness seem to have been fairly constant for at least 5000 years (Coren & Porac 1977) and probably longer. Evidence from the prehistoric record is necessarily indirect, but in a careful analysis of skeletal evidence and material cultural markers, Steele & Uomini (2005) suggested that the predominance of right-handedness was probably present in early species of our own genus, Homo, approximately 2 Myr ago.…”

“…This leaves approximately 33 per cent of people with the reversed asymmetry. One possibility is that the 90 per cent bias evident in human handedness and cerebral asymmetry reflects a genetic influence superimposed on a more general bias of approximately 67 per cent (Corballis 1997).…”