A Neurobiologist argues that the answer is scientifically well-defined
When discussing abortion issues the question of when does a human life actually begin is a critical one. If there is no “line in the sand” if you will then the answer to the question comes down to opinions about arbitrary points on life’s developmental timeline, and who’s to say which opinion is correct?
Fortunately, we can turn to science for an objective, precise answer to the question of when a human life begins.
In 2008, Dr. Maureen Condic, a Professor of Neurobiology and Anatomy at the University of Utah School of Medicine, published a white paper titled “When Does Human Life Begin? A Scientific Perspective.” The white paper can be downloaded at this link: http://www.bdfund.org/whitepapers
In the white paper, Dr. Condic argues that the beginning of a new human life can be scientifically well-defined “…independent of any specific ethical, moral, political, or religious view of human life or of human embryos.” Following is my interview with Dr. Condicto discuss some of the issues she wrote about in her whitepaper.
PLM: What was the motivation for creating this White Paper?
Dr. Condic: The question of when life begins impacts many important issues facing society: abortion, stem cell research, assisted reproductive technologies and human cloning, just to name a few.
And because people answer this question in a wide variety of ways, many feel it cannot be resolved objectively—that a consensus on this issue is impossible. Yet there is a great deal of misinformation and confusion about the basic scientific facts of early human embryology. And when you consider the facts from a strictly scientific perspective, there is a clear and unambiguous answer to the question of when human life begins.
PLM: You state in your paper that cellular life is a continuum, and because it is a continuum that this has led some to conclude that it is not possible to design a tea specific time at which human life begins. From the perspective of a develop mental biologist, how do you answer this line of thinking? From the perspective of science,how do we know we aren’t just choosing an arbitrary point on the developmental continuum?
Dr. Condic: The “continuum problem” is exactly what motivates many people to throw up their hands and conclude that the question of when life begins cannot be answered definitively. But there are clear, non-arbitrary transitions in the human life-cycle from one kind of thing to something entirely different.
For example, there are very real and unambiguous differences between a living person and a corpse. If we look objectively at what happens when sperm and egg fuse to create a one-cell embryo, there is an equally clear transition from two living human cells to a single living human organism. And the difference between a cell and an organism is both objective and non-arbitrary.
PLM: In the context of unique cellular composition, and unique cellular behavior, can you discuss briefly the process of sperm/egg interaction and what results from that interaction?
Dr. Condic: Sperm and egg cells are constructed in a very specific way to accomplish the goal of fertilization. There are a number of fascinating interactions between them before they come into direct physical contact that prepare the sperm to bind to the surface of the egg. But once the two cells are in physical contact, they undergo a very rapid process of cell fusion, where the outer surfaces of the two cells, their plasma membranes, join together. In this instant of cell fusion—less than a quarter of a second—a single cell is created that has a unique molecular composition, different from either sperm or egg, and that immediately starts behaving in ways that are very different from the behavior of either sperm or egg. This new cell, the zygote, takes an entirely new trajectory, initiating a complex series of molecular events that are directed towards the next steps of maturation—towards building the structures and relationships of the human body.
PLM: You discuss one of the processes of zygote development called “syngamy,” which you say is used as a marker by many to point to when human life begins. Can you describe briefly what syngamy is, why some believe this is the point of the beginning of life and not earlier, and what you believe science points to as the beginning of human life?
Dr. Condic: Many of events that occur during the first day following sperm-egg fusion are unique. Sperm and egg are highly specialized cells, and the structures they contribute to the zygote have to undergo significant modification before they can participate in human development. Historically, people have looked at these unique events as part of a“process”of fertilization,with the last step in this process being syngamy.
The genetic information contributed by the sperm and the egg initially exist in two separate structures known as “pronuclei”. At syngamy, the two pronuclei come together in the middle of the cell,and the membranes surrounding the DNA break down. This is the same process that occurs at every cell division in your body—the nuclear membranes dissolve so that the DNA can be separated equally into the two cells produced by cell division—but this event is given a special name in the zygote,because unlike all other cell divisions,this is the first time the DNA from the sperm and the egg are together in the same place within the cell. Because this is the last unique event following sperm-egg fusion, many medical text books point to syngamy as the end of the fertilization“process”, and claim it is the point at which the zygote forms and human life begins.
I reject this view for two reasons. First, syngamy is part of an ongoing developmental process that is clearly initiated a day earlier at sperm-egg fusion. Syngamy doesn’t alter the composition or behavior of the zygote, it is merely the next step in a journey that is already well under way. The point at which human life begins is the point at which the journey towards maturation begins. And this is clearly the point of sperm-egg fusion.
Second, biologically-speaking, syngamy is a non-event. Despite the poetic way syngamy is some times described—as the joining of the male and female nuclear information—there is no joining of the DNA and no formation of a single nucleus at syngamy.
Because the nuclear membrane has broken down, there is no nucleus at all. Because the nuclear membrane has broken down,there is no nucleus at all. And the DNA contributed by sperm and egg have been functioning as a single,unified genome ever since sperm egg fusion. Syngamy is a visually dramatic event,and a somewhat romantic one that appeals to people’s intuitive sense that there must be unification of the male and female gametes to create a baby. But this unification is fully complete in the instant of sperm-egg fusion—not at syngamy.
PLM: You talk about the importance of distinguishing “human cells” from a “human organism”. Can you discuss briefly why this distinction is important, and then classify which type the human zygote would come under and why.
Dr. Condic: The difference between a cell and an organism is profoundly important. There are about a hundred trillion cells in the mature human body. And all of these cells are parts that work together in a coordinated way for the good of the body as a whole.
This is the defining feature of an organism: it is a living being, composed of parts that work together for the life and health of the being as a whole.
A zygote is a single cell formed by the fusion of sperm and egg. And many people have a hard time thinking of a single cell as a living human being. But just as the parts of the mature body work together to promote the continued life and health of the body as a whole, all of the parts of the zygote work together in a coordinated manner to promote the continued health and development of the embryo as a whole.
The zygote “anticipates” and prepares for critical molecular and cellular events that will occur hours and even days later. Many of the molecular functions of the zygote only make sense in the context of this bigger, overall picture of human maturation. They are developmental processes,not merely cellular processes. Human cells—even human embryonic stem cells that are molecularly very similar to embryos—do not show this kind of globally coordinated interaction of parts for the good of the entity as a whole. They are not organisms.
PLM: In your paper you use the example of the process of “manufacturing a product” as a reason why some choose an arbitrary point on the developmental continuum to determine when life begins. Can you discuss this line of thinking and why you believe it is in correct?
Dr. Condic: We are familiar with the process of building something from parts. We bake cakes from a combination of flour,sugar and eggs. We build houses from 2x4s, nails and sheet rock. We manufacture cars from a bewildering number of mechanical parts.
In all cases, the thing we are building gradually comes into being. When does a pile of auto parts stop being a collection of metal and become a car? Clearly, there is no answer to this question, and different people will look at different arbitrary points in the process to decide when the object being assembled is“car-like enough”to be considered a car.
Embryonic development is similar to the more familiar process of manufacturing— the structures and relationships of the human body gradually come into being as a consequence of an ongoing developmental process. Because of this, many people choose an arbitrary point in the process when the embryo seems “human enough” to be considered a human. But the critical difference between manufacturing and embryonic development is that the embryo is constructing itself. There is no external builder who is putting the embryo together the way workers on an assembly line put a car together. The fact that the embryo undergoes a self-directed process of development means that the “builder” is present from the beginning of that process—from the instant of sperm-egg fusion onward.
PLM: Not related to your paper, but what areas of research are developmental biologists focusing on now?
What are the big questions to be answered in the next 10 years as pertains to scientific questions about human embryology?
Dr. Condic: The hottest topic in developmental biology right now is stem cell biology—or the general question of what enables a single cell to produce many different cell types. This is a fascinating question, and thanks to the insights of Dr. Shinya Yamanaka who won the Nobel prize last year for his work on cellular reprogramming, we have very powerful tools for studying this question. Many people are optimistic that this field will produce novel treatments for medical conditions. I am a bit more skeptical on that front, but it is clear that stem cell biology will enormously advance our understanding of human embryology and how specialized cell types are produced.
Dr. Condic is an Associate Professor of Neurobiology and Anatomy at the University of Utah School of Medicine. She received her undergraduate degree from the University of California at Berkeley. Since her appointment at the University of Utah in 1997, Dr. Condic’s primary research focus has been the development and regeneration of the nervous system. In 1999, she was awarded the Basil O’ Connor Young Investigator Award for her studies of peripheral nervous system development. In 2002, she was named a McKnight Neuroscience of Brain Disorders Investigator in recognition of her research in the field of adult spinal cord regeneration. In addition to her scientific research, Dr. Condic participates in both graduate and medical teaching. She is director of the University of Utah School of Medicine course in Human Embryology. She has published and presented seminars nationally on issues concerning science policy and the ethics of biological research. Dr. Condic currently resides in Salt Lake City with her husband and four children.
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