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Developmental Psychology 101: Development in Infancy


The Developmental Psychology 101 series addresses the theories, periods, and implications of development in a human life from conception all the way through to the stage of adolescence. Developmental psychology is a field which is studied by psychology students and academic researchers; its purpose is to understand individuals based on the biological and psychological changes they experience throughout their lifespan. Development is defined as modifications that momentarily or permanently change an organism in the journey from conception to death (Cole et al., 2005). This 101 series of articles will refer to development from a psychological perspective, discussing its social, emotional, cognitive, and physical areas. Moreover, the debate of nature versus nurture will be discussed in the development of the following four stages of life: prenatal period, infancy, childhood, and adolescence.

The Developmental Psychology 101 series is divided into six chapters:

4. Developmental Psychology 101: Development in Infancy

5. Developmental Psychology 101: Development in Childhood

6. Developmental Psychology 101: Development in Adolescence

Developmental Psychology 101: Development in Infancy

Infancy is the period of life that begins as the result of pushing in birth and continues through the process of learning and adapting until the age of two. The transition between fetal life and infancy is made by what some call the trauma of birth (Rank, 1924) and others the miracle of life. The fetus’ relationship with the environment dramatically changes the minute its little body is outside in the world, inhaling oxygen, getting adjusted to the light, being cold, and feeling a caregiver’s touch. Many changes occur during this stage of life, most of which revolve around cognitive and motoric development. The theories discussed in the first article of this 101 series will be used during this article to further explain what happens in human infancy. This article strives to explain why in infancy nature is the primary factor that facilitates development. The arguments and conclusions presented are based on the research of many scientists and theories with a focus on Jean Piaget, a psychologist known for his work with children; Sigmund Freud, the founder of psychoanalysis; and Erik Erikson, a developmental psychologist and psychoanalyst.

White woman with brown hair in a red dress lying on a single bed with a naked baby on her chest surrounded by a group of people

Figure 1: A home birth (Hagedorn, 1950-1959).

A Theoretical Approach to Infancy

Infancy represents the sensorimotor stage in Piaget’s theory (2008), as during this stage, humans learn to adapt to the environment and control the reflexes of their bodies until their actions become conscious and made with reason. The first sub-stage Piaget defines in the sensorimotor stage is the exercising reflex schema. In the first four to six weeks after birth, infants learn how to control their inborn reflexes, such as the constant movement of hands and feet, the Moro reflex, the grasping reflex, the sucking reflex, and more. Only in the next stage, which begins around the fourth week of life and completes at about four months of age, do babies begin showing basic acknowledgment of their actions. In this stage the action of thumb-sucking, for example, is repeated due to the pleasurable experience it entails. Piaget named this sub-stage primary circular reaction due to the fact that the attention of the baby focuses on a so-considered “primary” part of their body, and this is “circular” because the actions go back to themselves (Cole et al., 2005, p. 146). The other four sub-stages are focused on the development of the circular reaction and are as follows: secondary circular reaction, in which infants acknowledge that the movements they make have an effect on the environment; coordination of secondary circular reaction, in which the earliest form of problem-solving appears; tertiary circular reaction, a stage where experiments with consequences begin; and the beginning of symbolic representation, which commences invention and problem-solving through symbolic combinations (Cole et al., 2005, p. 178).

Another theoretical approach put forth by Freud delimits infancy in the psychosexual oral stage (1953). At this point in development, according to Freud, the mouth is the erogenous zone, as the child fulfills the feeding need through it. Not having mastered bowel and bladder control yet, one of the most entertaining body parts that a baby has is the mouth; therefore, it becomes the focus of knowledge, learning, pleasure, and expression, and it is contained in the oral stage. Moreover, from a social perspective on development, Erikson thinks infancy is the stage when trust forms (Eagle, 1997). Based on the fulfillment of their needs, infants learn to either trust their caregivers or begin to reject their authority. The most primitive attachment style forms between the caregivers and the infant, based on the fulfillment of the baby’s needs and the interaction between the two.

A woman in a white blouse and blue dress holds an infant in her arms with two young girls following behind her as they walk through along a path lined with tall pink flowers

Figure 2: Baby learning from the environment (Galerie Saint Martin, n.d.)

Mary Ainsworth, the psychologist who became the designer of attachment theory, based her research on the interaction between the caregiver and the infant and its life-long effects. While observing the infants’ behavior with their mothers, three general patterns of attachment arose: the secure one, the avoidant one, and the resistant one. A secure attachment allows the infant to continue to play comfortably while strangers are present, as long as the mother is also there. An avoidant attachment style shows a pattern of disinterest in regard to the presence of the mother and of indifference and lack of the need to be close to her. The resistant attachment style is the complete opposite with the infant needing to be as close as possible to the mother, becoming anxious when she leaves (Ainsworth et al., 1978). This social aspect of development not only affects the infant’s perception of life and relationships growing up but also influences these aspects of life in adulthood.

From a behaviorist point of view, infants learn through conditioning, whether it is classical or operant. In the frame of classical conditioning learning occurs when previous experience is linked to new stimuli, while in the frame of operant conditioning learning is shaped by the consequences of a behavior (Cole et al., 2005, p. 146). This is the stage when children start experiencing new stimuli and build their database of basic consequences and preferences, for example preferring the caregiver’s breast milk over a heated milk bottle. Another interesting aspect to take into consideration is the temperament with which babies are born. Temperament can be defined as the collection of responses an individual consistently has when faced with different stimuli of the environment. The connection between a baby’s temperament in infancy and their temperament in their adult life has been studied, and this relationship further proves the innate state of the temperament as it appears to be constant throughout life (Calinks & Degnan, 2005). If behaviors, attitudes, and thought patterns are learned, the first reactions to the environment as well as the adaptability level to the environment seem to be inherited. With this being said, one can affirm that nature is the primary factor that facilitates development in infancy.

drawing of a woman in pink and orange kneeling with a man in all green holding a girl in overalls and pigtails in a spherical dome while they are all surrounded by plants and flowers

Figure 3: Forming attachment in the developing stages (Deseret, 2022).

From a physical development perspective, the infant first learns how to control reflexes and to coordinate motions in infancy. Around six months after birth, infants can hold, shake, and grasp objects, and enjoy putting them in their mouth. In the span of one year, infants can bang objects together and place them inside or outside other objects; they are able to crawl, stand, and even walk. Moreover, the ability to form language comes only after a few months of learning to understand its meaning and make associations, so by their first birthday, children can produce basic language to request their needs. After a year and a half, infants can dress themselves, stack blocks, carry toys, and use pencils and other objects that require more advanced motoric control. When reaching the final year of infancy, the child can drink from straws, open cabinets, and use their imagination in playtime (Cole et al., 2005, p. 169). Physical development ensures the child will be able to meet the expectations of the environment and adapt to newer conditions such as exhaustion, temperature, and weather.

A baby’s capability to coordinate and control their actions in a new environment depends on their capacity to learn and adapt. This capacity is inherited from the people who contributed to the conception and is nurtured in the womb. Adaptation to the new environment requires a good attention span and focus from the baby, both of which are passed down through genes and activated by the process of birth by the stressors and reflexes that get triggered in this procedure (Cole et al., 2005, p. 110). The infant’s rudimentary ability to recognize their caregiver’s voices, the sensitivity to certain sounds of language, and the alertness while awake, are all genetic baggage that aid in the social development of the child as well as in the development of motor and cognitive skills. These skills are either learned by doing themselves or by being in the zone of proximal development, meaning they can learn the skills only with assistance or guidance (Vygotsky, 1987). Emotions are felt since birth, but the reactions to emotions seem to appear from the social cues infants receive from the humans that surround them. Once communication with the caregivers is established, a child will search for them to be their guide in a new environment. From looking comfortable to showing fear, the infant is basing their reactions on the caregivers' expressions (Slaughter & McConnell, 2003). Both biological and sociocultural processes contribute to the creation of a connection between the infant and the caregiver which allows the child to explore the environment in a safe way.

infographic of the stages of life from birth to 15 months explaining what milestones occur each month accompanied by illustrations of a baby doing each action outlined

Figure 4: Movement development in infancy stages (Armslikemoms, 2019).


Of course, one could argue that a baby learns by imitating the actions of others. That is true to an extent, as nature and nurture always interact for the improvement of a human’s competence. Without a head start received through better genes, a baby can struggle with adaptation, thus their development in infancy can suffer. With the help of the caregivers, the process of adjusting to the new environment can be made easier, as the adults learn the crying patterns; therefore, they will be able to feed the child and care for the child's needs. At this stage, nurture comes to keep the baby alive, to ensure that their needs are met, and that the environment is sufficiently stimulating for their best development. However, the primary factor that supports development in infancy is nature, as preferences for social interactions and food, and the reactions to the environment mold an infant into the adult they eventually become.

Bibliographical References

Ainsworth, M. D. S., Blehar, M. C., Waters, E., & Wall, S. (1978). Patterns of attachment: A psychological study of the strange situation. Mahwak, NJ: Lawrence Erlbaum Associates.

Calinks, S., & Degnan, K. (2005). Temperament in early development. In R. T. Ammerman (Ed.), Comprehensive handbook of personality and psychopatology: Vol 3. Child psychopatology. Hoboken, NJ: John Wiley & Sons.

Cole, M., Cole, S. R., & Lightfoot, C. (2005). The development of children (7th ed.). Worth Publishers, New York.

Eagle, M. (1997). Contributions of Erik Erikson. Psychoanalytic review, 84(3), 337-347.

Freud, S. (1953). Three essays on the theory of sexuality (1905). In Strachey, J. (Ed.) The standard edition of the complete psychological works of Sigmund Freud, volume VII (1901-1905): A case of hysteria, three essays on sexuality and other works (pp. 123-246). Vintage Classics.

Piaget, J., & Inhelder, B. (2008). The psychology of the child. Basic Books.

Rank, O. (1924). The trauma of birth in its importance for psychoanalytic therapy. Psychoanalytic Review, 11(3), 241-245.

Slaughter, V., & McConnell, D. (2003). Emergence of joint attention: Relationships between gaze following, social referencing, imitation, and naming in infancy. Journal of Genetic Psychology, 164, 54-71.

Vygotsky, L. S. (1987). The collected works of LS Vygotsky: Problems of the theory and history of psychology (Vol. 3). Springer Science & Business Media.

Visual Sources

Cover: Cassatt, M. (1896). Maternal caress [Painting]. Philadelphia Museum of Art. Retrieved from:

Figure 1: Hagedorn, K. (1950-1959). A home birth [Painting]. Art UK. Retrieved from:

Figure 2: Galerie Saint Martin. (n.d.). The stroll in the garden end of 19th century [Painting]. AnticStore. Retrieved from:

Figure 3: Morris, K. (2022). [Illustration of forming attachment in the developing stages]. Deseret News. Retrieved from:

Figure 4: Armslikemoms. (2019). Baby’s first year motor development [Illustration]. Retrieved from:


Author Photo

Raluca Reinerth

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