Twins regularly score nearly a standard deviation below the population mean on standardized measures of cognitive development in infancy but recover to the population mean by early childhood, making rapid gains through the toddler years. To date, only polynomial growth models have been fit to model cognitive recovery across childhood, limiting the…

In this article, it is argued that it makes sense to define and distinguish three levels of human intelligence: intelligence as genotypical potential, intelligence as actualised in environmental interaction, and intelligence as measured by tests (IQ). This raises the questions of what is meant by the term "intelligence as potential", and…

This study reanalyzes data presented by Ritchie, Bates, and Plomin (2015) who used a cross-lagged monozygotic twin differences design to test whether reading ability caused changes in intelligence. The authors used data from a sample of 1,890 monozygotic twin pairs tested on reading ability and intelligence at five occasions between the ages of 7…

Evidence from twin studies points to substantial environmental influences on intelligence, but the specifics of this influence are unclear. This study examined one developmental process that potentially causes intelligence differences: learning to read. In 1,890 twin pairs tested at 7, 9, 10, 12, and 16 years, a cross-lagged…

Objective: Bullying is the act of intentionally and repeatedly causing harm to someone who has difficulty defending him- or herself, and is a relatively widespread school-age phenomenon. Being the victim of bullying is associated with a broad spectrum of emotional problems; however, not all children who are bullied go on to develop such problems.…

Describes a methodology of behavior genetics in the context of twin and sibling/adoption design. This model was applied to cross-sectional data on cognitive development throughout the lifespan. Results from a twin and adoption study of general intelligence are presented to illustrate the use of the basic behavior genetic model in studying causes…

Appraised cognitive patterning and development for 142 pairs of twins at 4, 5, and 6 years of age. From the results it was inferred that within a broad range of home environments, the genotype exerts a significant influence on the child's cognitive development. (Author/SDH)

Stability of child and mother characteristics and the predictability of children's cognitive competence and affective characteristics were investigated as part of a longitudinal study. At 2 years of age, 46 sets of male twins and their parents were observed in the home and were rated for attachment, independence, compliance and conscience on the…

The hypothesis, that the importance of language to mankind lies not so much in the fact that it is the means by which we cooperate and communicate with each other as in the fact that it enables each of us, as individuals and in cooperation, to represent the world to ourselves as we encounter it, is presented. In infancy, the representation is made…

Background: Five DNA markers (single-nucleotide polymorphisms, SNPs) have recently been found to be associated with general cognitive ability "g") in a sample of 7414 7-year-old twins. These children have also been studied at 2, 3, 4, and 7 years of age on measures of cognitive and language development and behaviour problems; family environment…