Environmental Influences in Hand Preference: An African Point of View

Why are some people left-handed? An evolutionary perspective

“…This contrasts with a 6.5 per cent figure for Asian school children living in the United States, where cultural pressures have been reduced (Hardyck et al 1976). In two African countries (Ivory Coast and Sudan), the target activity against left hand use was eating and there remains strong cultural pressure for this activity (De Agostini et al 1997). In Japan, the proportion using the left hand for writing and eating are only 0.7 and 1.7%, respectively (Shimizu & Endo 1983), again suggesting strong cultural pressures.…”

“…writing or eating) did not condition hand preference for other tasks. (ii) De Agostini et al (1997) showed that the proportion of subjects with weak handedness is higher among those who reported earlier injuries causing a temporary shift of hand use. Bryden et al (1993) also observed that positive reinforcement for right hand use can modify patterns of handedness, and alter the relationships among different handedness tasks.…”

Is left-handedness associated with a more pronounced age-related cognitive decline?

“…It is a well-known fact that there were strong social directives against left-handedness until a few decades ago (and perhaps even today, at least in certain more urban societies; see Zverev, 2006). Social pressure can function in any of the following ways: (1) it may exert no influence whatsoever on preferred handedness; (2) it may affect certain behaviours that are under relatively high social pressure (such as writing and eating) while behaviours that are under less social pressure are not affected (such as throwing a ball); or (3) it may become generalised to all activities (De Agostini, Khamis, Ahui, & Dellatolas, 1997). The extent to which social pressure is successful in shifting the preferred hand from the left to the right side may be related to the age at which the pressure was exerted.…”

Hora de balanço

“…No que diz respeito ao efeito do sexo na preferência manual em adultos e idosos, os resultados, tal como nos outros momentos descritos, também se apresentam inconclusivos. Enquanto alguns estudos documentam a ausência de diferenças significativas entre sexos (109,110), outros observaram uma percentagem de homens sinistrómanos superior à de mulheres (82,111) . Um estudo recente de meta-análise sobre esta questão, efectuado por Sommer et al (112) , confirmou esta tendência.…”