Theoretical Medicine and Bioethics

, Volume 39, Issue 4, pp 301–319 | Cite as

Twin Inc.

  • Rose HershenovEmail author
  • Derek Doroski


This paper presents an account of how human spontaneous embryonic chimeras are formed. On the prevalent view in the philosophical literature, it is said that chimeras are the product of two embryos that fuse to form a new third embryo. We call this version of fusion synthesis. In contrast to synthesis, we present an alternative mechanism for chimera formation called incorporation, wherein one embryo incorporates the cells of a second embryo into its body. We argue that the incorporation thesis explains other types of chimera formation, which are better understood, and is more consistent than synthesis with what is known about embryological development. Incorporation also has different implications than synthesis and so avoids the philosophical puzzles that are often said to accompany embryonic chimera formation—puzzles which pose problems to the human embryo’s persistence from fertilization to the fetal stage of human development.


Human embryo Chimera Fusion 



We would like to thank participants at the Romanell Center 2016 Summer Conference and the 2018 Spring Romanell Center Worshop, as well as G. Koch, for helpful contributions to this paper.


  1. 1.
    Gilbert, Scott F. 2013. Developmental biology, 10th ed. Sunderland, MA: Sinauer.Google Scholar
  2. 2.
    Schoenwolf, Gary C., Steven B. Bleyl, Philip R. Brauer, and Philippa H. Francis-West. 2009. Larsen’s human embryology, 4th ed. Philadelphia: Churchill Livingstone.Google Scholar
  3. 3.
    van Inwagen, Peter. 1990. Material beings. Ithaca: Cornell University Press.Google Scholar
  4. 4.
    Smith, Barry, and Berit Brogaard. 2003. Sixteen days. Journal of Medicine and Philosophy 28: 45–78.CrossRefGoogle Scholar
  5. 5.
    Lee, Patrick, and Robert P. George. 2008. Body–self dualism in contemporary ethics and politics. Cambridge: Cambridge University Press.Google Scholar
  6. 6.
    Mintz, Beatrice. 1964. Formation of genetically mosaic mouse embryos and early development of “lethal (t12/t12)–normal” mosaics. Journal of Experimental Zoology 157: 273–292.CrossRefGoogle Scholar
  7. 7.
    Oderberg, David S. 1997. Modal properties, moral status, and identity. Philosophy and Public Affairs 26: 259–298.CrossRefGoogle Scholar
  8. 8.
    Napier, Stephen. 2013. Twinning, identity, and moral status. American Journal of Bioethics 13: 42–43.CrossRefGoogle Scholar
  9. 9.
    McMahan, Jeff. 2007. Killing embryos for stem cell research. Metaphilosophy 38: 170–189.CrossRefGoogle Scholar
  10. 10.
    Anscombe, G.E.M. 1984. Were you a zygote? Royal Institute of Philosophy Lecture Series 18: 111–115.Google Scholar
  11. 11.
    Ford, Norman. 1988. When did I begin? Conception of the human individual in history, philosophy and science. Cambridge: Cambridge University Press.CrossRefGoogle Scholar
  12. 12.
    Alvargonzalez, David. 2016. The constitution of the human embryo as substantial change. Journal of Medicine and Philosophy 41: 172–191.CrossRefGoogle Scholar
  13. 13.
    Sagan, Agata, and Peter Singer. 2007. The moral status of stem cells. Metaphilosophy 38: 264–284.CrossRefGoogle Scholar
  14. 14.
    Shoemaker, David W. 2005. Embryos, souls, and the fourth dimension. Social Theory and Practice 31: 51–75.CrossRefGoogle Scholar
  15. 15.
    Brown, Mark T. 2007. The potential of the human embryo. Journal of Medicine and Philosophy 32: 585–610.CrossRefGoogle Scholar
  16. 16.
    McMahan, Jeff. 1999. Cloning, killing and identity. Journal of Medical Ethics 25: 77–86.CrossRefGoogle Scholar
  17. 17.
    Ramsay, Marc. 2011. Twinning and fusion as arguments against the moral standing of the early human embryo. Utilitas 23: 183–205.CrossRefGoogle Scholar
  18. 18.
    Morris, Jason. 2012. Substance ontology cannot determine the moral status of embryos. Journal of Medicine and Philosophy 37: 331–350.CrossRefGoogle Scholar
  19. 19.
    Velez, Juan R. 2005. Immediate animation: Thomistic principles applied to Norman Ford’s objections. Ethics and Medicine 21: 11–28.Google Scholar
  20. 20.
    Lee, Patrick, and Robert George. 2006. Silver lining: A reply to Lee Silver. National Review, October 19.
  21. 21.
    Alberts, Bruce, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walker. 2002. Molecular biology of the cell, 4th ed. New York: Garland Science.Google Scholar
  22. 22.
    Carlson, Bruce M. 2009. Human embryology and developmental biology, 4th ed. Philadelphia: Mosby.Google Scholar
  23. 23.
    Wiltfred, H., and Sarah C. Hake. 2004. Principles of developmental biology. New York: W.W. Norton.Google Scholar
  24. 24.
    Wolpert, Lewis, Cheryll Tickle, Thomas Jessell, Peter Lawrence, Elliot Meyerowitz, Elizabeth Robertson, and Jim Smith. 2011. Principles of development, 4th ed. Oxford: Oxford University Press.Google Scholar
  25. 25.
    Adams, Cecil. 2009. Let’s talk about intersex, baby. Washington City Paper, February 6.
  26. 26.
    Owen, Ray D. 1945. Immunogenetic consequences of vascular anastomoses between bovine twins. Science 102: 400–401.CrossRefGoogle Scholar
  27. 27.
    Dunsford, I., C.C. Bowley, Ann M. Hutchinson, Joan S. Thompson, Ruth Sanger, and R.R. Race. 1953. A human blood group chimera. British Medical Journal 2: 81.CrossRefGoogle Scholar
  28. 28.
    Boklage, Charles E. 2010. How new humans are made: Cells and embryos, twins and chimeras, left and right, mind/self/soul, sex, and schizophrenia. Singapore: World Scientific Publishing.CrossRefGoogle Scholar
  29. 29.
    Park, Alice. 2015. How a man’s unborn twin fathered his child. Time, October 28.
  30. 30.
    Bianchi, Diana W., Gretchen K. Zickwolf, Gary J. Weil, Shelley Sylvester, and Mary Ann DeMaria. 1996. Male fetal progenitor cells persist in maternal blood for as long as 27 years postpartum. Proceedings of the National Academy of Sciences of the United States of America 93: 705–708.CrossRefGoogle Scholar
  31. 31.
    Srivatsa, Bharath, Sumathi Srivatsa, Kirby Johnson, and Diana Bianchi. 2003. Maternal cell microchimerism in newborn tissues. Journal of Pediatrics 142: 31–35.CrossRefGoogle Scholar
  32. 32.
    Chan, William F.N., Cécile Gurnot, Thomas J. Montine, Joshua A. Sonnen, Katherine A. Guthrie, and J. Lee Nelson. 2012. Male microchimerism in the human female brain. PLoS ONE 7: e45592. Scholar
  33. 33.
    Biase, Fernando H., Xiaoyi Cao, and Sheng Zhong. 2014. Cell fate inclination within 2-cell and 4-cell mouse embryos revealed by single-cell RNA sequencing. Genome Research 24: 1787–1796.CrossRefGoogle Scholar
  34. 34.
    Zdravkovic, Tamara, Kristopher L. Nazor, Nicholas Larocque, Matthew Gormley, Matthew Donne, Nathan Hunkapillar, Gnanaratnam Giritharan, et al. 2015. Human stem cells from single blastomeres reveal pathways of embryonic or trophoblast fate specification. Development 142: 4010–4025.CrossRefGoogle Scholar
  35. 35.
    Mansour, R.T., C.A. Rhodes, M.A. Aboulghar, G.I. Serour, and A. Kamal. 2000. Transfer of zona-free embryos improves outcome in poor prognosis patients: a prospective randomized controlled study. Human Reproduction 15: 1061–1064.CrossRefGoogle Scholar
  36. 36.
    Deglincerti, Alessia, Gist F. Croft, Lauren N. Pietila, Magdalena Zernicka-Goetz, Eric D. Siggia, and Ali H. Brivanlou. 2016. Self-organization of the in vitro attached human embryo. Nature 533: 251–254.CrossRefGoogle Scholar
  37. 37.
    Moore, Keith L., and T.V.N. Persaud. 2008. The developing human: Clinically oriented embryology, 8th ed. Philadelphia: Sauders.Google Scholar
  38. 38.
    Logroño, Roberto, Carlos Garcia-Lithgow, Charles Harris, Marijo Kent, and Lorraine Meisner. 1997. Heteropagus conjoined twins due to fusion of two embryos: Report and review. American Journal of Medical Genetics 73: 239–243.CrossRefGoogle Scholar
  39. 39.
    McMahan, Jeff. 2002. The ethics of killing: Problems at the margins of life. New York: Oxford University Press.CrossRefGoogle Scholar
  40. 40.
    Xhang, Xin, Petra Stojkovic, Stefan Przyborski, Michael Cooke, Lyle Armstrong, Majlinda Lako, and Miodrag Stojkovic. 2006. Derivation of human embryonic stem cells from developing and arrested embryos. Stem Cells 24: 2669–2676.CrossRefGoogle Scholar
  41. 41.
    Pearson, Helen, and Allison Abbot. 2006. Stem cells derived from ‘dead’ human embryo. Nature 443: 376–377.CrossRefGoogle Scholar
  42. 42.
    Chen, Kristen, Ramen H. Chmait, Douglas Vanderbilt, Wu Samuel, and Linda Randolph. 2013. Chimerism in monochorionic dizygotic twins: Case study and review. American Journal of Medical Genetics 161: 1817–1824.CrossRefGoogle Scholar
  43. 43.
    Tanaka, Mika, Anna-Katerina Hadjantonakis, Kristina Vintersten, and Andras Nagy. 2009. Aggregation chimeras: Combining ES cells, diploid, and tetraploid embryos. Methods in Molecular Biology 530: 287–309.CrossRefGoogle Scholar
  44. 44.
    Tarkowski, A.K. 1998. Mouse chimaeras revisited: recollections and reflections. International Journal of Developmental Biology 42: 903–908.Google Scholar
  45. 45.
    Karaman, Ibrahim, Derya Erdoğan, Semire Özalevli, Ayşe Karaman, M. Hakan Çavuşoğlu, Kemal Aslan, and Özden Çakmak. 2008. Fetus in fetu: A report of two cases. Journal of Indian Association of Pediatric Surgeons 13: 30–32.CrossRefGoogle Scholar
  46. 46.
    Boklage, Charles E. 2009. Traces of embryogenesis are the same in monozygotic and dizygotic twins: not compatible with double ovulation. Human Reproduction 24: 1255–1266.CrossRefGoogle Scholar
  47. 47.
    Hackmon, Rinat, Susan Jormark, Venessa Cheng, Christopher O’Reilly Green, and Michael Y. Divon. 2009. Monochorionic dizygotic twins in a spontaneous pregnancy: A rare case report. Journal of Maternal-Fetal and Neonatal Medicine 22: 708–710.CrossRefGoogle Scholar
  48. 48.
    Souter, Vivienne, Melissa A. Parisi, Dale R. Nyholt, Raj P. Kapur, Anjali K. Henders, Kent E. Opheim, Daniel F. Gunther, Michael E. Mitchell, Ian A. Glass, and Grant W. Montgomery. 2007. A case of true hermaphroditism reveals an unusual mechanism of twinning. Human Genetics 121: 179–185.CrossRefGoogle Scholar
  49. 49.
    Strain, Lisa, John C.S. Dean, Mark P.R. Hamilton, and David T. Bonthron. 1998. A true hermaphrodite chimera resulting from embryo: Amalgamation after in vitro fertilization. New England Journal of Medicine 338: 166–169.CrossRefGoogle Scholar
  50. 50.
    Simon-Bouy, B., M. Plachot, A. Mokdad, N. Lavaud, C. Muti, A. Bazin, F. Vialard, and J. Belaisch-Allart. 2003. Possible human chimera detected prenatally after in vitro fertilization: A case report. Prenatal Diagnosis 23: 935–937.CrossRefGoogle Scholar
  51. 51.
    Plachot, Michelle, B. Simon-Buoy, A. Mokdad, N. Lavaud, C. Muti, A. Bazin, F. Vialard, and J. Belaisch-Allart. 2002. Possible human chimera detected prenatally after in vitro fertilization: A case report. Fertility and Sterility 78: S146.CrossRefGoogle Scholar
  52. 52.
    Condic, Maureen L. 2014. Totipotency: What it is and what it is not. Stem Cells and Development 23: 796–812.CrossRefGoogle Scholar
  53. 53.
    Lee, Patrick, Christopher Tollefsen, and Robert P. George. 2014. The ontological status of embryos: A reply to Jason Morris. Journal of Medicine and Philosophy 39: 483–504.CrossRefGoogle Scholar
  54. 54.
    Koch-Hershenov, Rose. 2006. Totipotency, twinning, and ensoulment at fertilization. Journal of Medicine and Philosophy 31: 139–164.CrossRefGoogle Scholar

Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  1. 1.Department of PhilosophyNiagara UniversityLewistonUSA
  2. 2.Romanell Center for Clinical Ethics and the Philosophy of MedicineUniversity at BuffaloBuffaloUSA
  3. 3.Department of BiologyFranciscan University at SteubenvilleSteubenvilleUSA

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