A sex difference in the age of onset of the parent-child resemblance in intelligence.

Abstract

In a representative urban sample of 248 children, years of schooling of both parents showed an increasing relationship to their son's and daughter's IQs between 21 mo. and 15 yr. The parent-child correlation was observable and became statistically significant for girls by 3 yr. but not until 5 yr. for boys. Earlier parent-daughter resemblance was also noted when ratings of mother's intelligence and social status were correlated with the children's scores. Siblings' IQs yielded comparable sex differences in relation to parents' education. This finding was further confirmed in the correlations of the IQs of a 2nd generation sample with the IQs of the parent in the original group at age 15 yr. A sex difference in rate of mental growth is suggested as the major determinant of these results.

Stability and Change in Abilities Up to Five Years: Group Trends

“…These findings are consistent with those of Kagan and Moss (1959) and Honzik (1963), who reported an association between the child's I.Q,-and status characteristics of the parents, in their cases parental I.Q. and education, at an earlier age among girls than boys.…”

“…Scores at both ages were significantly correlated with mother's education, but only at 5 yr with that of the father. The generally higher correlations at 5 yr, with each of the parental status variables, are consistent with the findings of Bayley 1954) and Honzik (1957Honzik ( , 1963). Because of its high level of discrimination, father's occupation was used as the criterion of social class in further comparisons.…”

Developmental Changes in Mental Performance

“…The results from these several studies are quite consistent in suggesting that parental education begins to relate to the child's IQ performance between 11/ and 3/2 years for girls but not until 2/2 to 6 years for boys (Bayley & Jones 1937;Goodenough 1927;Hindley 1965;Honzik 1963;Kagan & Moss 1959;Moore 1968;Rees & Palmer 1970). Although the precise age at which the correlational relationship is first statistically significant varies among studies (i.e., presumably as a function of the nature of the sample, sample size, specific test instruments, testing regimen, etc.…”

“…Some investigators have found higher relationships with mother's education than with father's, especially during the 11/2-3-year period (Bayley & Jones 1937;Kagan & Moss 1959). Others do not find this parental sex difference (Goodenough 1927;Honzik 1963;Werner, Honzik, & Smith 1968), although the parental correlations may be higher for boys than girls (Werner et al 1968). …”

How does the strength of the relationships between cognitive abilities evolve over the life span for low-IQ vs high-IQ adults?

“…First, there is a great deal of evidence, in psychology, of developmental variations in the relationships between cognitive, demographic and background variables. For example, the correlation between parents' education or socioeconomic status and intelligence test scores of their offspring is negative or close to zero during early childhood but increases to .40-.60 in the following years (e. g., Bayley & Jones, 1937;Bayley, 1954Bayley, , 1970Honzik, 1957Honzik, , 1963Honzik, , 1967. Also, the IQ variance explained by genotype increases with age whereas the effect of shared environmental influences tends to diminish between childhood and adolescence (Plomin, 2003;Plomin, DeFries, McClearn, & McGuffin, 2001;Plomin & Petrill, 1997;Plomin & Spinath, 2004).…”