Birth Stress

Abstract

Chapters 4, 5, and 6 addressed themselves to the major classes of theories that have attempted to explain why populations of humans are predominantly right sided. These explanations included physiological and neurological predispositions, genetic factors, and environmental and sociocultural pressures. Although each approach could muster fairly cogent arguments for the population’s dextral bias, each had problems when attempting to explain the small but persistently recurring population of left-sided individuals. Left-siders are not clearly physiologically different; often they are born into families of right-sided parents, even where many previous generations have been right sided, and they are exposed to the same sociocultural and environmental pressures toward right-sidedness as dextrals. Yet they manifest sinistral tendencies, a fact that has puzzled many investigators. Somehow, despite the presence of the theoretically relevant factors, these individuals do not become right sided. Thus, it is not surprising that hypotheses were offered which explained sinistrality as an abnormal condition. In essence, these approaches are derived from the notion that the theories proposing universal right-sidedness are correct, and those individuals who do not conform to these theories are pathological. The particular mechanism of this inferred pathology and the nature of its action have varied from one theoretical position to another.