As reported recently in these pages, ("Stem Cells Discussed at Forum", Nov. 2), the debate continues in Massachusetts over when human life begins. A forum at Holy Cross College featured a discussion on this question between Professor Thomas Shannon, an ethicist at Worcester Polytechnic Institute and Father William Stempsey, a philosopher at Holy Cross. The debate is not just an academic one since state lawmakers are now considering how to deal with experiments in Worcester involving the destruction of newly conceived human embryos.

Shannon argued that the early embryo could not qualify as an individualized human being because "by definition", the "individual is indivisible". The stem cells of an early embryo may divide into separate organisms, such as happens with the creation of identical twins. In his view, human beings do not begin until the embryo passes the point at which twinning is still possible. Moreover, in Shannon’s opinion scientific research "suggests" that the early embryo lacks an "over-all organization" or internal unity among the stem cells so that it fails to qualify as a living organism of the human species.

What are we to make of these claims? They cannot be ignored because the Massachusetts courts have ruled that the homicide law protects human beings (as opposed to "persons"). Some people will argue that, at the very least, Shannon has created doubts about whether individual human beings are created at fertilization. Therefore, due to the resulting lack of consensus or certainty the legislature has no basis for protecting newly fertilized human embryos. The law, however, doesn’t work that way.

In every trial, the law presumes that a person charged with a crime or accused of a tort is innocent. The scales are tilted against conviction. The accused enjoys the benefit of any doubt. That means the burden rests on the shoulders of those who disagree with the presumption of innocence. They must produce compelling evidence that the accused is guilty or at fault. If the accusers can’t meet this heavy burden, then the accused goes free, even if the evidence offered to show innocence is itself subject to doubt. Why? Because it is better that a guilty person go free than an innocent person be condemned.

The question debated at Holy Cross and brought before the state legislature calls for the same decisional framework because, after all, a human being’s life may be at stake. If there is to be a consensus, then demand it of those who argue that individual human life is not at stake when an embryo is destroyed. Place a heavy burden squarely on their shoulders to achieve consensus by eliminating all reasonable doubt about their own position. Tilt the inquiry against destruction. Even if the proposition is debatable that life begins at fertilization, presume that it is true until refuted with evidence beyond a reasonable doubt. Why? Because it is better that non-life be mistakenly protected than for human life to be mistakenly taken.

Shannon claims that as long as identical twinning may occur an early embryo is not yet individualized. That is, until the twinning stage passes, the embryo must be unformed, and not yet determined to be the individual it will grow up as. Everything depends, however, on his definition of an individual, which he says is someone that is "indivisible". Shannon’s case is weakened by the fact that his definition is not the only reasonable one out there.

Aristotle defined the term individual by referring to an entity’s capacity to exist separately from other beings, a capacity marked by an internal working together of the entity’s parts. This classical definition allows for the possibility that an individual could, while currently possessing its separateness from other beings and its internal unity, divide in the future.

Aristotle’s definition of individual permits us to point to the separateness and integrity of the early embryo to prove his or her individualization as classically understood. Even though the early embryo may have the potential of losing some cells through identical twinning or through a lab technician’s manipulation, his or her original separateness would endure and his or her remaining cells could continue to work together to reach maturity. Where there was just the original individual, there is now that same individual and a newly created twin whose separate existence began at the time of twinning. Science confirms that fertilization is not the only way that new living beings, including human beings, can be created.

Aristotle’s definition raises a reasonable doubt indicating that Shannon’s interpretation of twinning might be wrong. Rather than existing as an unformed non-entity as posited by Shannon, the early embryo could be classified as an individual under Aristotle’s definition because of its separation from other beings and its internal unity. Unless Aristotle’s definition is refuted as philosophically untenable, and its application to the early embryo denied by science, a rational basis continues to support the presumption that an early embryo is an individual human being.

Shannon argues that the scientific evidence does "suggest" that the early embryo lacks internal unity. Here again, Shannon’s assertion is, at the very least, subject to reasonable doubt.

In 1995-96, Shannon participated in a debate on the moral status of the human embryo in a series of articles published in the prestigious journal "Theological Studies". He interacted with a theologian Mark Johnson, who concluded after a careful examination of embryological studies that even before twinning "there is a remarkable, even symphonic, cooperation of the cells of the zygote."

Johnson’s summary of the scientific evidence, including data showing the rarity of identical twinning, prompted Shannon to concede in one of his responses in the series that there is "certainly an arguable position" that "at most, provides a reason for acting as if the zygote were a human person". Shannon admitted that the exchange of views between Johnson and himself "can be characterized, I think, as analogous to the debate about whether a glass is half empty or half full".

Precisely. There are two competing arguments. Which side should the law take? Should it presume that the glass is entirely empty, that the embryo is not a human being? Should it ignore the averages of nature dictating that nearly all but a tiny percentage of embryos will continue to develop without twinning?