What do the results of twins studies on IQ say about John Locke’s theory?
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Here are some quotes to assist you in this nature vs nurture debate. The last really answers your question. The others mainly point out the fallacies psychologists delude themselves in thinking what they do is science, and that they are using mathematical reasoning.
"....our main conclusion after some years of work on this problem is that mathematical estimates of heritability tell us almost nothing about anything important."
C.JENCKS, 1972, Inequality. New York : Basic Books.
"....in the absence of experimental controls in which genetically identical individuals are assigned at conception to different random environments, the confounding effects of the environment (intra-uterine and external) with the genotype can never be eliminated." K.RICHARDSON & J.M.BYNNER, 1984, International Journal of Psychology 19.
"Am I precluding the study of human behavior genetics? Not at all....I {merely} believe that the realm of the possible is far more circumscribed than has been recognized in the current largely worthless literature being produced by the careerists (Plomin, 1989, 1990; Bouchard et al., 1990). The task of a scientifically sound human behavior genetics is challenging but not impossible of execution. It will involve studying the behavioral consequences of known genes."
J.HIRSCH, 1990, Cahiers de Psychologie Cognitive 10.
"It amazes me how many graduate students and even colleagues think that giving a psychological test to monozygotic and dizygotic twins makes one a geneticist. The number of naive estimates of h² from twin correlations published in the literature with no mention whatsoever of profound methodological problems is symptomatic of the malaise."
D.WAHLSTEN, 1990, Cahiers de Psychologie Cognitive 10.
"[Burn & Goodship found that of one MZ twin, by the process of inactivation of the surplus X chromosome] had an excess of the mother's X, the other was just as likely to have only the father's, or some of the mother's and some of the father's, or all of the mother's-it didn't seem to matter. Yet the MZ girls as a group showed more skewing than DZ girls. "Whatever causes identical twinning, these studies show that even though identical twins share the same genes, a genetic trait does not have to be shared," Burn says. "The English language is misleading in calling these twins identical-perhaps we should use the German term eineiige, 'one-egg'." ....A few identical twins are so different that they don't resemble each other any more closely than ordinary siblings. Some researchers suspect that certain differences, particularly in behavior, result from their separating early in embryogenesis, and therefore coming to term in separate placentas."
Lawrence WRIGHT, 1995, 'Double mystery.'
New Yorker, 7 viii, 44-62.
"Donald Hebb doubted the possibility of estimating heritability at all, and compared the effort to sort our the relative contributions of heredity and environment to obviously absurd efforts to sort out which is more important in deciding the size of a field-its length or breadth.... We must re-phrase Hebb: given a large number of rectangular fields, which is more influential in affecting differences in size between them - length or width, and is there any interaction between the two? That is a question which is quite easy to answer, using the statistical techniques known as analysis of variance;.... it is certainly not nonsensical or unanswerable."
H.J.EYSENCK, 1981.
"[Steven Rose, in his letter on 'The Burt business' says] the heritability of human traits cannot be determined because humans cannot be selectively bred. On the contrary, virtually every textbook on human genetics describes procedures for heritability estimation. Half of the articles in the most recent issue of Genetic Epidemiology, the premier international journal devoted exclusively to analytical methods in human genetics, report heritability estimates or describe methods for heritability estimation."
Thomas J. BOUCHARD et al., 1993, Times Literary Supplement, 19 ii.
"[In 160 same-sex Croatian twin pairs, aged 15-19], intraclass correlations for monozygotic and dizygotic twins were, respectively,
.75 and .44 for visualization;
.58 and .33 for spatial orientation;
.67 and .41 for word fluency; and
.74 and .41 for vocabulary."
D.BRATKO (University of Zagreb), 1995, from the abstract of an address to International Society for the Study of Individual Differences, meeting in Warsaw.
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The provided quotes do not directly address John Locke's theory of intelligence in relation to twin studies and IQ. The quotes mainly discuss the limitations and challenges of estimating heritability and the complexities of studying genetic and environmental influences on human behavior.
To understand the results of twin studies on IQ and their implications for John Locke's theory, it is necessary to explore the actual research and findings in the field of behavioral genetics. Twin studies compare the similarities in IQ scores between identical twins (monozygotic twins, who share 100% of their genetic material) and fraternal twins (dizygotic twins, who share around 50% of their genetic material). If IQ is mostly influenced by genetics, then identical twins should have more similar IQ scores compared to fraternal twins.
Research on twin studies has consistently shown that genetics plays a significant role in individual differences in IQ. Identical twins raised in separate environments (adopted separately) tend to have more similar IQ scores compared to fraternal twins raised in separate environments. This indicates that genetic factors contribute to the IQ similarities observed in identical twins.
However, it is important to note that the environment also plays a role in shaping IQ. Twin studies have also shown that the environmental factors shared by twins, such as family upbringing and socio-economic background, have an influence on IQ scores. These shared environmental factors can contribute to IQ similarities between both identical and fraternal twins.
Overall, the results of twin studies suggest that both genetics and environment contribute to individual differences in IQ. This aligns with a more nuanced view of intelligence that incorporates both nature and nurture, rather than supporting a purely one-sided theory such as John Locke's.
To get a more comprehensive understanding of the relationship between twin studies on IQ and John Locke's theory, it would be beneficial to consult relevant research articles, books, and scholarly sources in the field of behavioral genetics and intelligence.