The Biology of Temperament and Support Strategies for Infant Educators

By: Derrick Toups, M.Ed.

Educators and parents often observe that, even from birth, babies display their own unique sleep patterns, sensitivity levels, and reasons for crying. These early indicators of individuality are known as temperament, a theoretical construct of “constitutionally based individual differences” that are primarily rooted in genetics and biology (Gross, 2024, p. 264). While a child’s personality and idiosyncrasies will continue to evolve as they age, temperament provides powerful insight into the innate ways a child responds to and interacts with the world.

Alexander Thomas and Stella Chess introduced the concept of temperament in the 1960s. As outlined in Figure 1, they identified several innate traits, with either low or high expressions, which can help caregivers better understand and respond to the unique expression of these in each baby. They simplified these into three major classifications: easy, difficult, and slow to warm up, which are also referred to as resilient, undercontrolled, and overcontrolled (Caspi & Shiner, 2006).

Figure 1

Expression of Thomas & Chess' Temperaments

Adapted from Thomas and Chess (1977). Copyright Rice University, OpenStax, under CC BY NC-SA 4.0 license.

How a child expresses these temperaments depends on the child’s genetics, physiology, and unique developmental trajectory. Neuroscience and prenatal research from the past three decades have identified several biological influences on temperament which help caregivers understand the origins of certain temperament expressions.

●      Prenatal heart rate is related to activity. Research suggests that temperament begins to emerge in the womb. Greater variability in fetal heart rate has been correlated with higher emotional reactivity and irritability after birth (Pingeton et al., 2021), and highly active fetuses tend to become infants who are more active, less predictable, and less adaptable (DiPietro et al., 1996). This suggests that parents may be able to predict certain components of their child’s temperament before they are even born.

●      Neural networks are related to regulation and affect. Researchers have identified the specific neural networks linked to how individuals regulate their emotions and behaviors as well as the networks correlated with negative affect (Kelsey et al., 2021; Howarth et al., 2016). Work by Kagan (2013) found that differences in dopamine receptors are linked to an infant’s ability to be soothed, providing further context for the biological basis of certain temperaments.

●      The nervous system is related to reactivity. Highly-reactive infants may be genetically predisposed to a lower threshold for the activation of the sympathetic nervous system (the “fight or flight” response), while less-reactive infants have a higher threshold for this activation (Kagan, 1994). A more recent study by Martinez-Torteya (2026) suggested that maternal stress during pregnancy was linked to higher reactivity and fear distress in infants. What presents as difficult behavior in infants may actually be a physiological response to a perceived threat, often due to a lower biological threshold.

The work of Thomas & Chess and the biological science behind temperament challenge infant educators to move away from one-size-fits-all caregiving and toward a more nuanced understanding of who each individual child is. Because infants place different demands on their caregivers based on their temperament, self-reflection is also a key component to successfully supporting infants. Chess & Thomas introduced the concept of “goodness of fit” which refers to the match between a child’s temperament and their caregiving environment (1984). For example, a high-activity child may thrive more with a high-energy caregiver or one who provides sufficient opportunities for physical movement. By recognizing a child’s unique temperament and how it aligns or challenges their own disposition, caregivers can more effectively create an environment that supports their own mental health as well as the needs of the individual child. Below are a few practical strategies that can help infant teachers embrace the unique temperament of different children.

●      Tailor or differentiate the physical environment. Modify the physical space to accommodate different activity levels. For high activity children, ensure the classroom or outdoor space has designated areas and equipment that support crawling, climbing, rolling, and jumping. For more sedentary children, provide sufficient time and encouragement to explore movement.

●      Strategically plan for transitions. Reference each child’s adaptability and rhythmicity/regularity when planning routines. For children with unpredictable or irregular biological schedules, acknowledge the importance of meeting their unique needs even when they deviate from the more predictable schedules of others. For less adaptable children, even those who are not speaking yet, provide advanced notice of transitions and narrate what you are about to transition into in order to help them mentally prepare for a change in activity. Provide time and patience to support less adaptable children through transitions.

●      Provide support and reassurance. For infants who are difficult to soothe or who exhibit a negative affect, closely observe the infant’s cues before intervening and provide a response that matches the specific need, such as comfort or a change of pace or activity. For children with cautious adaptability, serve as a safe base for them when less-familiar adults enter the environment and provide reassurance and comfort.

●      Match the infant’s temperament. Adjust your own energy and volume to match the child’s intensity and sensitivity levels. With an active or high-intensity child, use an enthusiastic tone and active body language. With a more sensitive child, use a calm, steady approach to avoid overwhelming them.

References

Caspi, A., & Shiner, R. L. (2006). Personality development. In W. Damon & R. M. Lerner (Eds.), Handbook of child psychology: Social, emotional, and personal development (6 ed., Vol. 3, pp. 300-365). Wiley.

Chess, S., & Thomas, A. (1984). Origins and evolution of behavior disorders: From infancy to early adult life. Harvard University Press.

DiPietro, J. A., Hodgson, D. M., Costigan, K. A., & Johnson, T. R. (1996). Fetal antecedents of infant temperament. Child Development, 67(5), 2568–2583. https://doi.org/10.2307/1131641

Gross, D. (2024). Infancy: Development from birth to age three (4th ed.). Rowman & Littlefield.

Howarth, G. Z., Fettig, N. B., Curby, T. W., & Bell, M. A. (2016). Frontal electroencephalogram asymmetry and temperament across infancy and early childhood: An exploration of stability and bidirectional relations. Child Development, 87(2), 465–476. https://doi.org/10.1111/cdev.12466 

Kagan, J. (1994). On the nature of emotion. Monographs of the Society for Research in Child Development, 59(2/3), 7–24. https://doi.org/10.2307/1166136  

Kagan, J. (2013). Temperamental contributions to inhibited and uninhibited profiles. In P. D. Zelazo (Ed.), The Oxford handbook of developmental psychology, Vol. 2. Self and other (pp. 142–164). Oxford University Press.

Kelsey, C. M., Farris, K., & Grossmann, T. (2021). Variability in infants’ functional brain network connectivity is associated with differences in affect and behavior. Frontiers in Psychiatry, 12. https://doi.org/10.3389/fpsyt.2021.685754

Martinez-Torteya, C., Nuttall, A. K., Bogat, G. A., Levendosky, A. A., & Lonstein, J. S. (2026). Timing of prenatal stress exposure predicts infant sympathetic nervous system and affective responses. Developmental Psychobiology, 68(2). https://doi.org/10.1002/dev.70140 

Pingeton, B. C., Goodman, S. H., & Monk, C. (2021). Prenatal origins of temperament: Fetal cardiac development & infant surgency, negative affectivity, and regulation/orienting. Infant Behavior & Development, 65. https://doi.org/10.1016/j.infbeh.2021.101643

Thomas, A., & Chess, S. (1977). Temperament and development. Brunner/Mazel.

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Derrick Toups teaches education and child development courses at Tulane and multiple Louisiana community colleges and is an early childhood Ph.D. student at LSU. He can be contacted at derricktoups@gmail.com.

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