Example: In cultures where babies receive early training in sitting up, standing, and walking, they develop these skills earlier. Conversely, in other cultures, mothers carry babies most of the time, and babies develop these skills later.


Some babies have fussy personalities, while others have chirpy or quiet natures. These differences result from temperament, the kind of personality features babies are born with. Researchers generally agree that temperament depends more on biological factors than on environment. In the 1970s, Alexander Thomas and Stella Chess, two researchers who study temperament, described three basic types of temperament: easy, slow to warm up, and difficult. In their research, 40 percent of the children were easy, 15 percent were slow to warm up, and 10 percent were difficult. The remaining 35 percent of the children displayed a mixture of these temperaments:

  • Easy children tend to be happy and adapt easily to change. They have regular sleeping and eating patterns and don’t upset easily.
  • Slow-to-warm-up children tend to be less cheerful and less adaptable than easy children. They are cautious about new experiences. Their sleeping and eating patterns are less regular than those of easy children.
  • Difficult children tend to be glum and irritable, and they dislike change. Their eating and sleeping patterns are irregular.


Attachment is the close bond between infants and their caregivers. Researchers used to think that infants attach to people who feed them and keep them warm. However, researchers Margaret and Harry Harlow showed that attachment could not occur without contact comfort. Contact comfort is comfort derived from physical closeness with a caregiver.

The Harlows’ Baby Monkeys

The Harlows raised orphaned baby rhesus monkeys and studied their behavior. In place of its real mother, each baby monkey had two substitute or surrogate mothers. One “mother” had a head attached to a wire frame, warming lights, and a feeding bottle. The other “mother” had the same construction except that foam rubber and terry cloth covered its wire frame. The Harlows found that although both mothers provided milk and warmth, the baby monkeys greatly preferred the cloth mother. They clung to the cloth mother even between feedings and went to it for comfort when they felt afraid.

Responsive Mothering

Psychologist Mary Ainsworth and her colleagues found that attachment happens through a complex set of interactions between mothers and infants. The infants of sensitive, responsive mothers have stronger attachments than the infants of insensitive mothers or mothers who respond inconsistently to their infants’ needs. However, an infant’s temperament also plays a role in attachment. Difficult infants who fuss, refuse to eat, and sleep irregularly tax their mothers, which makes it hard for the mothers to be properly responsive.

Attachment Styles

Ainsworth devised an experiment called the Strange Situation in order to study attachment behavior. She asked each mother in the sample to bring her infant to an unfamiliar room that contained various toys. After the mother and infant had spent some time in the room, a stranger entered the room and tried to play with the infant. A short while later, the mother left the room, leaving the infant with the stranger. Then the mother returned to the room, and the stranger left. A little later, the mother left the room again, briefly leaving the infant alone. Finally, the mother returned to the room.

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