Abstract
There is currently no consensus on when human life begins, and consequently, the biological, moral, and legal status of early human embryos is unclear. Here, the biological facts concerning early human development are examined to establish a scientific view of when human life begins. The evidence clearly indicates that a new human organism (i.e., a human being) is formed at the point of sperm–egg fusion. The events occurring during preimplantation development provide further support for the conclusion that the early embryo is an organism. The status of the zygote as a complete organism is contrasted to that of human pluripotent stem cells that are best understood as parts of an organism. Two common arguments for assigning human rights to developing human beings are outlined and their logical implications are briefly discussed, in light of the scientific facts regarding human development.
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Notes
- 1.
“An Act Respecting Assisted Human Reproduction and Related Research (Bill C-6),” Canada/Government, Ottawa (29 March 2004).
- 2.
“An organism of the species Homo sapiens during the earliest stages of development, from 1 cell up to 8 weeks”, Human Chimera Prohibition Act of 2005, S. 659, 109th Cong. (2005).
- 3.
“Federal Embryo Protection Law” (1990) (Bundesgesetzblatt, Part 1, December 19, 1990, pp. 2746–2748).
- 4.
Human Fertilisation and Embryology Act 2008, Part 1, (2). Available at: http://www.opsi.gov.uk/acts/acts2008/ukpga_20080022_en_1.
- 5.
Nicholas Agar argues that embryos produced in the laboratory do not have rights because they lack a functional relationship with the womb, a sentiment mirrored by Senator Orrin Hatch.
- 6.
For example, the Guidelines for Conduct of Human Embryonic Stem Cell Research published by the largest scientific society of stem cell researchers in the world (International Society for Stem Cell Research: http://www.isscr.org/guidelines/index.htm (accessed Dec 1, 2008) do not explicitly define when life begins, yet allow research on human embryos up to 14 days postfertilization, or until the appearance of the primitive streak (typically seen at 14 days).
- 7.
Merriam Webster defines “organism” as “(1) a complex structure of interdependent and subordinate elements whose relations and properties are largely determined by their function in the whole and (2) an individual constituted to carry on the activities of life by means of organs separate in function but mutually dependent: a living being.” http://www.merriam-webster.com/dictionary/organism (accessed Dec 1, 2008).
- 8.
The great majority of studies done on early mammalian development have been done in mice. Although the general pattern of early development observed in mouse and human embryos is very similar, relatively little is known specifically about the molecular and cellular interactions occurring in early human development. However, recent studies of nonhuman primates (reviewed in Byrne et al. 2006) demonstrate a strong degree of similarity between mouse and monkey development, suggesting that much of what has been determined for mouse embryos is likely to be true for human embryos as well.
- 9.
Structures derived from TE (e.g., placenta) do not contribute to the postnatal body and have classically been considered “extraembryonic” (i.e., outside the embryo), a term that is often misinterpreted as “non-embryonic.” However, TE-derived tissues are clearly part of the embryo, not part of the mother or of some other entity that coexists with the embryo. Like all embryonic structures, those derived from TE are (1) generated by the embryo, (2) physically continuous with the embryo, (3) genetically identical to the embryo, and (4) critically required for embryonic function and survival. TE-derived structures are best considered transient organs of the embryo and fetus, i.e., bodily structures/organs that function only during prenatal life. Other examples of organs with transient functions are the lungs (functioning only during postnatal life) and the ovaries (functioning as reproductive organs only between puberty and menopause).
- 10.
Unlike birds or amphibians that have large eggs, with enough nutrients to support the developing embryo until hatching, mammals have relatively small, nutrient-poor eggs that can only support development for a few days. Without the mother as a source of food and oxygen, the embryo would not survive. Thus, implantation and establishing contact with the circulatory system of the mother are critical to the health and development of the embryo as a whole.
- 11.
It is sometimes claimed that once the brain has acquired sufficient maturity to “potentially” support cognition, actual manifestation of cognitive acts is not required for an individual to be considered human, but this argument does not define “potential” in terms of either biological structures or neurological function and thus seems to be a version of the “Social convention form” discussed below.
- 12.
The United Nations Convention on the Rights of Persons with Disabilities and Optional Protocol (http://www.un.org/esa/socdev/enable/dispaperdes0.htm; accessed Dec 1, 2008). Entered into force on 3 May 2008, after receiving its 20th Ratification. A total of 67 countries have ratified the Convention or Optional Protocol.
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Condic, M.L. (2011). Preimplantation Stages of Human Development: The Biological and Moral Status of Early Embryos. In: Suarez, A., Huarte, J. (eds) Is this Cell a Human Being?. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-20772-3_3
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