ClaimsSteven Pinker

“Growing up together doesn't make you more similar in intelligence or in personality over the long run.”

Steven Pinker, interviewee 1 January 2002 A Biological Understanding of Human Nature (Edge.org) archived copy

Factual Science and research methods

Twins separated at birth are no more different in intelligence and personality than twins raised together; growing up together does not make people more similar in the long run.

Mostly true True in substance, wrong in a detail.

Factual: Statements about the present or the past, checked against the record: did they hold up?

What would count as true or false

The claim is that a shared family environment (growing up together) does not lastingly make people more similar in intelligence or personality. True: behavioural genetic research as of about 2002 (twin, adoption and reared-apart studies such as MISTRA and SATSA) shows the shared-environment contribution to adult IQ and personality to be near zero, and twins reared apart to be about as similar as twins reared together. Mostly true: the finding holds broadly, with a minor qualification (e.g. a small residual shared-environment effect, or the effect showing for IQ only by adulthood while it is substantial in childhood). Mixed: the evidence supports the claim for one trait (e.g. personality) but not the other. Mostly false: the research shows meaningful lasting shared-environment effects for most measures, and the claim generalises a narrow finding. False: the evidence shows that being reared together substantially and lastingly increases similarity in both traits.

Set before the research began.

Evidence (4)

  1. E1 Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart Science (American Association for the Advancement of Science); authors Bouchard, Lykken, McGue, Segal, Tellegen · 12 October 1990

    “monozygotic twins reared apart are about as similar as are monozygotic twins reared together.”

  2. E2 Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart Science (American Association for the Advancement of Science); authors Bouchard, Lykken, McGue, Segal, Tellegen · 12 October 1990

    “(ii) the effect of being reared in the same home is negligible for traits.”

  3. E3 Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart Science (American Association for the Advancement of Science); authors Bouchard, Lykken, McGue, Segal, Tellegen · 12 October 1990

    “In any case, a significant contribution of shared environment is found for the personality trait of social closeness (31), and possibly religious interests and values (32).”

  4. E4 Nature versus nurture WikiDoc · 4 September 2012

    “Moreover, adoption studies indicate that, by adulthood, adoptive siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6.”

Reasoning

The Minnesota Study of Twins Reared Apart reports that identical twins raised apart are about as similar as identical twins raised together, and that being raised in the same home has a negligible effect on the traits it measured (E1, E2). A later secondary summary says adoption studies find adoptive siblings no more alike in adult IQ than strangers (E4). The same study also reports a significant shared-environment effect for the personality trait of social closeness, and possibly for religious interests and values (E3). That small exception fits the "mostly true" category in the criteria.

Cite this claim

Steven Pinker, “Twins separated at birth are no more different in intelligence and personality than twins raised together; growing up together does not make people more similar in the long run.” (said 1 January 2002). Verdict: mostly true. Reliability API, claim c_3dfd121ea3b9, method 0.1.0+28da144b, dataset release v1.1.2. https://epistacklabs.com/claims/c_3dfd121ea3b9

This claim is in dataset release v1.1.2, with the same verdict.

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All of them

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