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Altruistic Behavior among Twins

Willingness to Fight and Self-Sacrifice for Their Closest Relatives

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A Correction to this article was published on 22 November 2017

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Abstract

According to kin selection theory, indirect reproductive advantages may induce individuals to care for others with whom they share genes by common descent, and the amount of care, including self-sacrifice, will increase with the proportion of genes shared. Twins represent a natural situation in which this hypothesis can be tested. Twin pairs experience the same early environment because they were born and raised at the same time and in the same family but their genetic relatedness differs depending on zygosity. We compared the degree of willingness to fight and sacrifice for the co-twin among monozygotic (MZ) and dizygotic (DZ) pairs in a sample of 1443 same-sex and opposite-sex twins. We also analyzed the effect of the subject’s gender and that of the co-twin on those altruistic behaviors. Results partly supported the postulated explanation. MZ twins (who share nearly their entire genome) were significantly more likely than DZ twins (who on average share half of their segregating genes) to self-sacrifice for their co-twins, but zygosity did not affect willingness to fight for him/her. The genders of the subject and of the co-twin, not genetic relatedness, were the best predictors of aggressive altruistic intentions.

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  • 22 November 2017

    The original version of this article unfortunately contained a mistake. The presentation of the article title and subtitle was incorrect.

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Acknowledgments

The authors wish to thank the twins participating in the Murcia Twin registry for their collaboration and commitment. The Murcia Twin Registry is supported by Fundación Séneca, Regional Agency for Science and Technology, Murcia, Spain (08633/PHCS/08, 15302/PHCS/10 & 19479/PI/14) and Ministry of Economy and Competitiveness (MINECO), Spain (PSI2009-11560 & PSI2014-56680-R). UNED group is also supported by MINECO, Spain (PSI2015-67754-P).

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Authors and Affiliations

  1. Department of Human Anatomy and Psychobiology, University of Murcia, 30100, Murcia, Spain

    Encarnación Tornero, Juan F. Sánchez-Romera, José J. Morosoli & Juan R. Ordoñana

  2. Department of Social and Organizational Psychology, National Distance Education University (UNED), Madrid, Spain

    Alexandra Vázquez & Ángel Gómez

  3. Murcia Institute for Biomedical Research (IMIB-Arrixaca-UMU), University Hospital Virgen de la Arrixaca, 30120, Murcia, Spain

    Juan R. Ordoñana

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  1. Encarnación Tornero
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  2. Juan F. Sánchez-Romera
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  3. José J. Morosoli
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  5. Ángel Gómez
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  6. Juan R. Ordoñana
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Correspondence to Juan R. Ordoñana.

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Ethical Approval

MTR participants were contacted through postal letter invitation, which contained information regarding the objectives of the registry and study information. Twins were later contacted by telephone. Oral informed consent was obtained from all individual participants included in the study, prior to any data collection taking place. All MTR procedures, including informed consent and data collection for this study, was approved by the Murcia University Ethical Committee. National regulations regarding personal data protection were followed. All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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The original version of this article was revised due to incorrect presentation of the article title and subtitle.

A correction to this article is available online at https://doi.org/10.1007/s12110-017-9308-9.

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Tornero, E., Sánchez-Romera, J.F., Morosoli, J.J. et al. Altruistic Behavior among Twins. Hum Nat 29, 1–12 (2018). https://doi.org/10.1007/s12110-017-9304-0

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