HomeoldWhy the human zygote is an organism (and why it matters)

Why the human zygote is an organism (and why it matters)

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In the public debate surrounding embryo-destructive biomedical research, many individuals dismiss the assertion that the human zygote and blastocyst/young embryo (the earliest stages of human prenatal development following conception) are human beings, on the grounds that other cells and tissues, such as a patch of skin cells, or the sperm and egg, are also living and human, yet no one supposes that they are themselves human beings. However, these critics appear to be poorly informed about the biological facts.

The key distinction is that zygotes and embryos are living organisms, whereas skin cells, sperm and eggs are not. The zygote/embryo is a distinct human organism, that is to say, a human being, a self-developing member of the species Homo sapiens, at a very early stage of life. Other cells are merely components of larger wholes, and do not constitute individual organisms.

However, the term “organism” requires elucidation. Dr. Maureen L. Condic, a Berkeley-educated neurobiologist and professor at the University of Utah School of Medicine, where she teaches human embryology, elucidates:

The term “organism” is defined 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.” This definition emphasises the interdependence of parts within a unified whole as the defining characteristic of an organism.

This definition has led to the proposal that human beings (including embryonic human beings) can be reliably distinguished from human cells using the same criteria employed by scientists to distinguish different cell types: by examining their composition and their pattern of behaviour. A human being (i.e., a human organism) is composed of characteristic human parts (cells, proteins, RNA, DNA), yet it is different from a mere collection of cells because it has the characteristic behaviour of an organism: it acts in an interdependent and coordinated manner to “carry on the activities of life”. In contrast, collections of human cells are alive and carry on the activities of cellular life, yet fail to exhibit coordinated interactions directed towards any higher level of organisation. Collections of cells do not establish the complex, interrelated cellular structures (tissues, organs, and organ systems) that exist in a whole, living human being. Similarly, a human corpse is not a living human organism, despite the presence of living human cells within the corpse. This is because the collection of human cells no longer functions as an integrated unit.

The question thus arises as to whether the zygote can be considered an organism. Condic proceeds to elaborate:

From the moment of fertilisation, the human zygote is a complete entity, with all its constituent parts interacting in a coordinated manner to generate the structures and relationships required for the zygote to continue developing towards its mature state. Prior to fusion, the actions of the sperm and egg are specifically ordered to facilitate the binding of these two cells. Subsequent to the point of sperm-egg fusion, the zygote engages in a series of actions that are specifically designed to prevent further binding of the sperm and to facilitate the preservation and development of the zygote itself. The zygote initiates a program of development immediately and with decisive action. If this program is not interrupted by accidents, disease, or external intervention, it will proceed seamlessly through the formation of the genitive body, birth, childhood, adolescence, maturity, and aging, and will end with death. This coordinated behaviour is a defining feature of an organism.

In contrast, human cells are composed of human DNA and other human molecules, yet they exhibit no global organisation beyond that intrinsic to cells in isolation. A human skin cell removed from a mature body and maintained in a laboratory setting will continue to live and will divide numerous times to produce a large mass of cells. However, it will not re-establish the whole organism from which it was removed. It will not regenerate an entire human body in culture. Although embryogenesis commences with a single-cell zygote, the intricate, interrelated process of embryogenesis is the function of an organism, not the activity of a cell.

A scientific description of fertilisation, the fusion of sperm and egg in the “moment of conception”, indicates that a new human cell, the zygote, is generated with a composition and behaviour distinct from that of either gamete. Moreover, this cell is not merely a unique human cell; it is a cell with all the properties of a fully complete (albeit immature) human organism. It is “an individual constituted to carry on the activities of life by means of organs separate in function but mutually dependent: a living being.”

Condic concludes:

The embryo is formed at the moment of fertilisation, when the sperm and egg merge. From this point onwards, the human organism is fully present, controlling and directing all of the developmental events that occur throughout life. This view of the embryo is objective, based on the universally accepted scientific method of distinguishing different cell types from each other, and it is consistent with the factual evidence. This definition is entirely independent of any specific ethical, moral, political, or religious view of human life or of human embryos. It is evident that this definition does not directly address the central ethical questions surrounding the embryo. These include the following: What value ought society to place on human life at the earliest stages of development? Does the human embryo possess the same right to life as do human beings at later developmental stages? A neutral examination of the factual evidence establishes that the onset of a new human life occurs at a scientifically well-defined “moment of conception.” This conclusion unequivocally indicates that human embryos from the zygote stage forward are indeed living individuals of the human species—human beings.

The scientific community has established that the embryo is an individual human organism, a human being, at the embryonic stage of life. It is not within the purview of science to dictate how the embryo ought to be treated. This is a moral (as opposed to scientific) question.

If, as pro-life advocates argue, human beings possess intrinsic moral value and there is a fundamental equality among all members of our species, irrespective of size, age, ability and condition of dependency, then the destruction of embryonic human beings for their stem cells is similarly unacceptable as the killing and harvesting of the useful parts of a 10-year-old child for the benefit of others.


Daniel Miller is responsible for nearly all of National Right to Life News' political writing.

With the election of Donald Trump to the U.S. presidency, Daniel Miller developed a deep obsession with U.S. politics that has never let go of the political scientist. Whether it's the election of Joe Biden, the midterm elections in Congress, the abortion rights debate in the Supreme Court or the mudslinging in the primaries - Daniel Miller is happy to stay up late for you.

Daniel was born and raised in New York. After living in China, working for a news agency and another stint at a major news network, he now lives in Arizona with his two daughters.

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