448 Part V Biological/Evolutionary Theories
Evidence suggests that temperament and personality differences are manifest
even before birth, prenatally. Apparently, fetal activity and heart rate can reveal some-
thing about temperament differences over the first year of life (DiPietro et al., 1996).
In particular, a high heart rate at 36 weeks’ gestation (nearly full term) foreshadowed
less predictable eating and sleeping habits 3 and 6 months after birth and less emo-
tionality at 6 months after birth. Having high activity levels at 36 weeks’ gestation
predicted being slow to adapt to new people or situations and having more irregular
eating and sleeping habits at 3 and 6 months as well as being more difficult or fussy
at 6 months (DiPietro et al., 1996).
The prenatal environment plays an important role in shaping personality. In
fact, the amount of stress the mother experiences during pregnancy may alter the
infant’s own stress response. That is, infants born to mothers who have experienced
an unusual amount of stress during pregnancy tend to have impaired stress func-
tion; higher baseline levels of stress hormones; and a faster, stronger, and more
pronounced physiological response to stress, all of which persist into childhood
(Barbazanges et al., 1996; Clark & Schneider, 1997).
After birth, in the immediate post-natal period, newborn infants already dis-
play regular and consistent differences in behavior; that is, they have distinct tem-
peraments (A. Buss, 2012). These behavioral differences are most pronounced in
four dimensions of temperament: activity, emotionality, sociability, and impulsiv-
ity. Activity is simply how active the baby is and how much energy he or she uses
in doing things, that is, how quickly or slowly the newborn does things. Emotion-
ality is seen in how frequently and intensely the baby experiences either positive
or negative emotion, that is, how happy or fussy the baby is. Some research has
shown that infant distress is associated with anxiety disorders in mothers soon after
birth (Reck et al., 2013). Sociability concerns the baby’s response to other people,
especially strangers. Some babies are sociable and outgoing and others withdraw
and cry or are reserved and shy in the presence of strangers (Clarke-Stewart, Umeh,
Snow, & Peterson, 1980). Finally, impulsivity involves the readiness and speed to
act, without reflection. All infants are relatively impulsive but even in infancy there
are consistent differences between babies. These differences tend to become more
noticeable during childhood and adolescence. Moreover, long-term research has
reported that toddlers who have impulsive temperaments are more likely than other
toddlers to commit criminal activity and have difficulty with alcohol by the time
they reach age 21 and also perform worse academically and have lower SAT scores
(Caspi, 2000; Mischel, Shoda, & Rodriguez, 1989).
Temperament assessed in childhood and adolescence can also predict teen
substance abuse (Tarter, 2002). For example, Neighbors and colleagues (2000)
recruited more than 400 adolescents (mean age of 16) from an adolescent alcohol
research center. These teenagers completed a self-report measure of temperament
(Dimensions of Temperament Survey, DOT) that measures ten dimensions of tem-
perament: activity, sleep, approach/withdrawal, flexibility/rigidity, quality of mood,
sleep regularity, eating regularity, daily routine, distractibility, and persistence.
Researchers classified teens into a “difficult temperament” category if they were
consistently on the extreme low (activity or sleep) or high end of the scores on
temperament. Alcohol abuse was assessed via a clinical interview and for each
“clinically present” symptom the participant received a score of 1. These standards