Human birth order and personality traits

¶ … Psychology of Human Birth Order and Personality

Introduction to the Biological Relevance of Birth Order:

In nature, birth order is related directly to survival rates of offspring in many nonhuman animal species. Generally, first-borns are slightly larger, more physically robust, and healthier, and possess a continuing advantage competing with their siblings for resources. When resources become scarce, firstborns often become the sole focus of parental attention and in many species (particularly among birds), they may push their younger siblings from the nest, peck them to death, or even eat them for nourishment (Gerrig & Zimbardo, 2008).

In humans, birth order also confers definite advantages, but with greater variation and complexity. During human evolution birth order undoubtedly directly affected survival rates as it still does today in many undeveloped parts of the world. In developed countries, birth order is more related to personality and cognitive development than to physical survival although it is still associated with measurable physiological differences with first borns being slightly taller, more intelligent, and more professionally successful than later borns. These general propositions are widely accepted but they are subject to different theoretical explanations (Gerrig & Zimbardo, 2008; Kluger, 2007).

Birth Order Influence on Personality Development:

In addition to characteristic physiological differences associated with birth order, first borns and later borns often exhibit characteristic personality and intellectual differences. First borns are more likely to have higher IQs, to adopt parental values, and to exemplify societal expectations in their choices and professional career paths. Meanwhile, later borns tend to have slightly lower IQs, to rebel more against family values and expectations, and to violate social rules of conformity in their behavioral choices and career paths (McWilliams, 2004).

The influence of birth order on human personality becomes even more complex when one considers middle children. In addition to being exposed to different types of developmental experiences than either first borns or last borns, middle children are also the only ones whose status in the family never changes. First borns experience being the youngest child in the family and last borns eventually experience being the only child remaining in the family; middle children never have any of the benefits of only children or youngest children. As a result, middle children tend to seek attention more than either first borns or last borns, even to the extent of criminal deviance (Gerrig & Zimbardo, 2008; Kluger, 2007).

The Theoretical Basis of Birth Order Influence

The three main explanations for the influence of birth order on human personality development are (1) physiological factors, (2) better access to parental resources, and (3) the cognitive effects of their experiences as only children first and then as surrogate parents (in many respects) to their younger siblings (Hockenbury & Hockenbury, 2007). According to physiologists, mother's milk is richest in nutrients and beneficial growth factors after their first pregnancy and their testosterone level highest during gestation. Behaviorists report that first born children receive greater parental attention and nutrition than later born siblings. Finally, psychologists suggest that first borns tend to have higher self-esteem because of their experiences as surrogate caretakers for their siblings and higher intelligence because of the cognitive effects of having to supervise and teach younger siblings while helping parents care for them (Travis & Kohli, 1995).