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The relationship between fertility and intelligence has been investigated in many demographic studies, although there is no conclusive evidence of a positive or negative correlation between human intelligence and fertility rate. Survival rates are, however, correlated with IQ, but the net effect on population intelligence is unclear. It is theorized that if an inverse correlation of IQ with fertility rate were stronger than the correlation of survival rate, and if heritable factors involved in IQ were consistently expressed in populations with different fertility rates, and if this continued over a significant number of generations, it could lead to a decrease in population IQ scores. However, the Flynn Effect demonstrates a clear general increase in measured IQ scores over time. Other correlates of IQ include income and educational attainment,〔 which are also inversely correlated with fertility rate, and are to some degree heritable. ==Early views and research== A negative correlation between fertility and intelligence (as measured by IQ) has been argued to have existed in many parts of the world at various times.〔(Literacy, Education and Fertility, Past and Present: A Critical Review, Harvey J. Graff )〕 Some of the first studies into the subject were carried out on individuals living before the advent of IQ testing, in the late 19th century, by looking at the fertility of men listed in Who's Who, these individuals being presumably of high intelligence. These men, taken as a whole, had few children, implying a correlation.〔Huntington, E., & Whitney, L. ''The Builders of America.'' New York: Morrow, 1927.〕〔Kirk, Dudley. 'The fertility of a gifted group: A study of the number of children of men in WHO'S WHO.' In ''The Nature and Transmission of the Genetic and Cultural Characteristics of Human Populations.'' New York: Milbank Memorial Fund, 1957, pp.78–98.〕 Nobel Prize–winning physicist William Shockley controversially argued from the mid-1960s through the 1980s that "the future of the population was threatened because people with low IQs had more children than those with high IQs."〔William Shockley, Roger Pearson: ''Shockley on Eugenics and Race: The Application of Science to the Solution of Human Problems'' Scott-Townsend Publishers, ISBN 978-1-878465-03-0〕 In 1963, Weyl and Possony asserted that comparatively small differences in average intelligence can become very large differences in the very high I.Q. ranges. A decline in average psychometric intelligence of only a few points will mean a much smaller population of gifted individuals.〔Weyl, N. & Possony, S. T: The Geography of Intellect, 1963, s. 154〕 More rigorous studies carried out on Americans alive after the Second World War returned different results suggesting a slight positive correlation with respect to intelligence. The findings from these investigations were consistent enough for Osborn and Bajema, writing as late as 1972, to conclude that fertility patterns were eugenic, and that "the reproductive trend toward an increase in the frequency of genes associated with higher IQ... will probably continue in the foreseeable future in the United States and will be found also in other industrial welfare-state democracies." Several reviewers considered the findings premature, arguing that the samples were nationally unrepresentative, generally being confined to whites born between 1910 and 1940 in the Great Lakes States. Other researchers began to report a negative correlation in the 1960s after two decades of neutral or positive fertility. In 1982, Daniel Vining sought to address these issues in a large study on the fertility of over 10,000 individuals throughout the United States, who were then aged 25 to 34. The average fertility in his study was correlated at −0.86 with IQ for white women and −0.96 for black women. Vining argued that this indicated a drop in the genotypic average IQ of 1.6 points per generation for the white population, and 2.4 points per generation for the black population.〔 〕 In considering these results along with those from earlier researchers, Vining wrote that "in periods of rising birth rates, persons with higher intelligence tend to have fertility equal to, if not exceeding, that of the population as a whole," but, "The recent decline in fertility thus seems to have restored the dysgenic trend observed for a comparable period of falling fertility between 1850 and 1940." To address the concern that the fertility of this sample could not be considered complete, Vining carried out a follow-up study for the same sample 18 years later, reporting the same, though slightly decreased, negative correlation between IQ and fertility.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fertility and intelligence」の詳細全文を読む スポンサード リンク
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