Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart found in prior studies is due to similarity in their environments. A reanalysis using Taylor's classification of environments but an alternative IQ measure shows that his findings do not constructively replicate. (Author/RD)

This paper presents the results of a study which examined heritability ratios for the major ethnic and socioeconomic groups in the Los Angeles Unified School District. Scores on three measures (the Cooperative Primary Reading Test, the Comprehensive Test of Basic Skills, and a composite set of intelligence tests) were compared for twins from…

A classification of natal influences is proposed with a model of their operation. Natal influences affect maternal capacity, maternal load, and maternal efficiency. Since maternal load is increased in twin pregnancy, results of twin studies must be generalized with caution. The method of co-twin control is exemplified by examination of a small…

A study of twins was conducted to determine the presence of an hereditary component in short term memory and in three aspects of verbal divergent thinking--flexibility, fluency, and originality. Results showed the existence of a significant genetic component in the trait of short term memory, while none was found in verbal divergent thinking. (AG)

This book is organized in nine parts, as follows. Part I, "Preface," includes an account of how the author went from the rather esoteric research on theoretical problems in serial rote learning to research on the inheritance of mental abilities and its implications for education. Part II, "How Much Can We Boost IQ and Scholastic Achievement?," is…

A case study of a pair of extremely deprived twin boys focuses on their verbal communication. Talkativeness alone was not regarded as a measure of intelligence, but attention was paid to the less talkative twin's greater use of imaginative speech. Speculations are made on the evolutionary role of creative speech. (IS)