Challenges and adaptations (WTP) 

Tactile and auditory sensitivities in toddlers Some adults and children are more sensitive to touch and sound than others. Mothers reported their children's sensory experiences over a wide distribution, with some accumulation of individuals experiencing very strong sensitivities. Mothers reported more girls in the "very sensitive" group. Sensory experiences were modestly related to fearful behavior and anxious behavior, but they were relatively distinct from other common dimensions of childhood personality and behavior. Goldsmith, H. H., Van Hulle, C. A., Arneson, C. L., Schreiber, J. E., & Gernsbacher, M. A. (2006). A population-based twin study of parentally reported tactile and auditory defensiveness in young children. Journal of Abnormal Child Psychology, 34, 378-392. Twin and parent similarity in late afternoon stress hormones Modest family similarity was apparent for afternoon basal cortisol levels (a stress hormone). Mothers and fathers' cortisol levels were also correlated. Family resemblance in afternoon cortisol was accounted for by features of shared environment, but not underlying genetic factors. Female children had higher cortisol levels than males, and cortisol decreased with age until about 9 years of age, after which cortisol increased with age. Shared family experiences influence parent and child stress hormone levels throughout the childhood years. Schreiber, J. E., Shirtcliff, E., Van Hulle, C., Lemery-Chalfant, K. S., Klein, M. H., Kalin, N. H., Essex, M. J., & Goldsmith, H. H. (2006). Environmental influences on family similarity in afternoon cortisol levels: Twin and parent-offspring designs. Psychoneuroendocrinology, 31, 1131-1137. Twin similarities on social and emotional behavior in toddlers In general, parents report identical toddler twins to be more similar to one another than fraternal twins on a range of behaviors. Twin similarity is used to calculate heritability. In this sample, heritability accounted for 56% or more of the variation in observed behavior. Differences between twins were primarily due to unique experiences. Girl and boy toddlers showed similar patterns in the underlying causes of behaviors. Van Hulle, C. A., Lemery-Chalfant, K., & Goldsmith, H. H. (2007). Genetic and environmental influences on socio-emotional behavior in toddlers: An initial twin study of the Infant-Toddler Social and Emotional Assessment (ITSEA). Journal of Child Psychology and Psychiatry, 48, 1014-1024. Overview of literature examining whether genetic influences contribute to the development of childhood temperament Research suggests that several dimensions of temperament including anger/frustration, behavioral inhibition/fear, activity level, and effortful control are heritable. There is also emerging evidence suggesting that many of the same genetic influences that impact the personality development ( e.g. anger/frustration) also contribute to the manifestation of child behavior problems (e.g. conduct problems). Gagne, J. R., Vendlinski, M. K., & Goldsmith, H. H. (in press, 2008). The genetics of childhood temperament. In Y-K Kim (Ed.). Handbook of Behavioral Genetics. New York: Springer.