Jane Maienschein, writing in Slate, imagines that chimeras undercut the case that human embryos should be protected from being deliberately killed.
We know that some cases exist in which two eggs are fertilized inside a woman quite naturally, and the genetically different cells divide but then touch each other and grow together. . . .
In perhaps the biologically most intriguing cases, the two combine more completely. Two different lines of cells, with different genes on different chromosomes, come together and, with the amazing regulatory powers of life, merge together to make a whole, apparently normal and natural chimeric person. The case of Karen Keegan brought chimerism to medical attention in 1998, when her sons were being tested as possible kidney donors for her. They failed to match her DNA in ways that suggested that they could not be her sons, yet she (and her family) knew they were. Doctors finally discovered that she had two distinct sets of DNA, which proved that chimerism does occur and yet remain invisible.
So here’s Maienschein’s payoff:
What does such developmental complexity mean for the proposed Sanctity of Human Life Act? If one twin absorbs part of the other, did it commit homicide? Perhaps so. . . . What about a chimeric person—does he or she get two votes because of having come from two different fertilizations? If fertilization defines personhood, then surely so.
Clearly, this easily leads to nonsense.
And the legislation Maienschein discusses, whatever its merits in general, is invulnerable to her objection because it stipulates that the life of a human being “begins with fertilization, cloning, or its functional equivalent.” The formation of a chimera could involve three fertilization or fertilization-equivalent events: the formation of each initial embryo, and then their combination into a new human embryo. At no point would it be proper, from the perspective of the pro-life law under discussion, to kill any of these human embryos. From that perspective there were two human lives worth protecting, which then ended and were replaced by a new human life worth protecting. He or she should get one vote, eventually.
The point of including the phrase “or its functional equivalent” in the legislative text—the only conceivable point, if you’ll permit the adjective—is to cover cases like Keegan’s. It is to say, that is, that living human organisms—which is what human beings at any developmental stage are—deserve protection; and they deserve that protection as soon as they come to be. Maienschein’s claim that pro-lifers are ignorant of biology is false, and rooted in her own ignorance of the pro-life position.