10. What can twins tell us about nature and nurture?

1 I cite several examples of such claims in my book Black Brain, White Brain: Is Intelligence Skin Deep?, Jonathan Ball, 2014.

2 Study by Nancy Segal cited in Erika Hayasaki, ‘Identical Twins Hint at How Environments Change Gene Expression’, The Atlantic, 15 May 2018.

3 Jim Springer, quoted in ‘“Jim Twins” return to university for more tests’, Associated Press, 5 November 1987.

4 Erika Hayasaki, op. cit.

5 Cited in ‘“Jim Twins” return to university for more tests’, Associated Press, 5 November 1987.

6 Nancy Segal, quoted in Erika Hayasaki, op. cit.

7 Nancy Segal, quoted in Susan Dominus, ‘The Mixed-Up Brothers of Bogota’, New York Times Magazine, 9 July 2015.

8 Francis Galton, ‘The history of twins as a criterion of the relative powers of nature and nurture’, Fraser’s Magazine 12, 1875, pp. 566–76.

9 Matt Ridley, Nature via Nurture, Fourth Estate, London, 2003, p. 75.

10 See N. Langstrom, et al., ‘Genetic and environmental effects on same-sex sexual behaviour: a population study of twins in Sweden’, Archives of Sexual Behavior 39 (1), February 2010, pp. 75–80.

11 Ian Sample, ‘Genetics accounts for more than half of variation in exam results’, Guardian, 11 December 2013.

12 Nicholas Shakeshaft, et al., ‘Strong Genetic Influence on a UK Nationwide Test of Educational Achievement at the End of Compulsory Education at Age 16’, PLoS One 8 (12) e80341, 11 December 2013, p. 5.

13 Ibid., p. 8.

14 This is a high number (today there are 33 twin births per 1,000; more than when I was a child), and the ratio is unusual (one quarter of multiple births are identical twins).

15 B. Devlin, et al., ‘The heritability of IQ’, Nature 388 (6641), 1997, pp. 468–71.

16 Leon Kamin, The Science and Politics of IQ, Penguin, London, 1977.

17 Letter from Cyril Burt to William Shockley, 10 April 1971, quoted in Ronald Fletcher, Science, Ideology and the Media: The Cyril Burt Scandal, Transaction Publishers, 1991, p. 381.

18 Ibid., p. 378.

19 Ronald Fletcher, op. cit.

20 H. J. Eysenck, quoted by Gould, op. cit., p. 265.

21 Robert Joynson, The Burt Affair, Routledge, 1989.

22 Ronald Fletcher, op. cit.

23 Leslie Hearnshaw, Cyril Burt: Psychologist, Hodder and Stoughton, London, 1979.

24 ‘Sir Cyril Burt’, Encyclopaedia Britannica entry, 2013, http://www.britannica.com/related-places/85886/related-places-to-Sir-Cyril-Burt

25 See for example Rob Newman, ‘Total Eclipse of Descartes: The Inheritance’, BBC Radio 4, 14 September 2018 https://www.bbc.co.uk/radio/play/b0bh5hp2

26 M. Savastano, et al., ‘Psychological characteristics of patients with Meniere’s disease compared with patients with vertigo, tinnitus, or hearing loss’, Ear Nose & Throat Journal 86 (3), 2007, pp. 148–56.

27 M. R. Rosenweig, et al., ‘Effects of environmental complexity and training on brain chemistry and anatomy: A replication and extension’, Journal of Comparative and Physiological Psychology 55 (4), 1962, pp. 429–37.

28 Gould, op. cit., p. 266.

29 Wickliffe Preston Draper, quoted in Ridley, op. cit., p. 81.

30 The Pioneer Fund website, www.thepioneerfund.org

31 Linda Gottfredson, et al., ‘Mainstream Science on Intelligence’, public statement published in the Wall Street Journal, 13 December 1994.

32 Ridley, op. cit., p. 81.

33 Susan Farber, Identical Twins Reared Apart, Basic Books, New York, 1981.

34 Cited by Professor Jack Kaplan, ‘How to inherit IQ: an exchange’, New York Review of Books, 30 November 2006.

35 Leon Kamin, quoted in ‘A study of twins bred apart produces some curious discoveries’, The Hour, 14 October 1981.

36 Thomas J. Bouchard Jr, et al., ‘Sources of human psychological differences: the Minnesota Study of Twins Reared Apart’, Science 250, 1990, p. 225.

37 Robert Plomin, Blueprint: How DNA Makes Us Who We Are, Allen Lane, 2018, pp. 54–5.

38 Ibid., p. 57.

39 James Flynn, What Is Intelligence? Cambridge University Press, Cambridge, 2009, p. 39.

40 Ibid., p. 90.

41 Eric Turkheimer, quoted in David L. Kirp, ‘After the Bell Curve’, New York Times Magazine, 23 July 2006.

42 Steven Rose, ‘Commentary: heritability estimates – long past their sell-by date’, International Journal of Epidemiology 35 (3), June 2006, p. 527.

43 Paul Ehrlich, Human Natures: Genes, Cultures and the Human Prospect, Penguin, 2002, p. 11.

44 Robert Plomin, 2018, op. cit., p. 55.

45 Alexander Young, et al., ‘Relatedness disequilibrium regression estimates heritability without environmental bias’, Nature Genetics 50, 13 August 2018, pp. 1304–10.

46 Bouchard, et al., 1990, op. cit., p. 224.

47 Ibid.

48 Ibid., p. 227.

49 Richard Nisbett, quoted in John-Paul Flintoff and Jonathan Leake, ‘How to make your child more intelligent’, Sunday Times, 17 May 2009.

50 Thomas Bouchard, quoted in Arthur Allen, ‘Nature and Nurture’, Washington Post Magazine, 11 July 1998.

51 Robert Plomin, 2018, op. cit., p. 55.

52 Leon Kamin, quoted in N. Mackintosh, IQ and Human Intelligence, Oxford University Press, Oxford, 1998, pp. 78–9.

53 Ridley, op. cit., p. 90.

54 Ibid.

55 Research by Christiane Capron and Michel Duyme, New York Review of Books, 2006, op. cit.

56 Ridley, op. cit., pp. 90–1.

57 New York Review of Books, op. cit.

58 See Eric Turkheimer, ‘Individual and group differences in adoption studies’, Psychological Bulletin 110 (3), 1991, p. 398.

59 Linda Gottfredson, et al., op. cit.

60 Robert Plomin 2018, op. cit., pp. viii and ix.

61 Richard Nisbett 2009, op. cit.

62 Stephen Jay Gould, The Mismeasure of Man, Penguin, 1997, p. 185.

63 Ibid.

64 Ibid., p. 186.

65 Borrowed from John Loehlin, ‘On Schönemann, on Guttman, on Jensen, via Lewontin’, Multivariate Behavioral Research 27 (2), 1992, p. 261.