I have a very deep admiration for the late great Carl Sagan. He has influenced and shaped my thoughts on many issues. In a series of essays he wrote together with his wife Anne Druyan, he has sketched a solution to the slippery slope on the abortion debate. I believe he has found the middle ground for any reasonable person.
If you are still stuck on the horns of the false dichotomy I outlined in my previous post, you should perhaps read the entire series of four essays here:
For my purposes, the conclusion is what counts. The article is quite long and refers in depth to American case law, so I have had to shorten it somewhat (sorry Carl)
If you deliberately kill a human being, it's called murder. If you deliberately kill a chimpanzee--biologically, our closest relative, sharing 99.6 percent of our active genes--whatever else it is, it's not murder.
To date, murder uniquely applies to killing human beings. Therefore, the question of when personhood (or, if we like, ensoulment) arises is key to the abortion debate. When does the fetus become human? When do distinct and characteristic human qualities emerge?
We recognize that specifying a precise moment will overlook individual differences. Therefore, if we must draw a line, it ought to be drawn conservatively--that is, on the early side. There are people who object to having to set some numerical limit, and we share their disquiet; but if there is to be a law on this matter, and it is to effect some useful compromise between the two absolutist positions, it must specify, at least roughly, a time of transition to personhood.
Every one of us began from a dot. A fertilized egg is roughly the size of the period at the end of this sentence. The momentous meeting of sperm and egg generally occurs in one of the two fallopian tubes. One cell becomes two, two become four, and so on—an exponentiation of base-2 arithmetic. By the tenth day the fertilized egg has become a kind of hollow sphere wandering off to another realm: the womb. It destroys tissue in its path. It sucks blood from capillaries. It bathes itself in maternal blood, from which it extracts oxygen and nutrients. It establishes itself as a kind of parasite on the walls of the uterus.
By the third week, around the time of the first missed menstrual period, the forming embryo is about 2 millimeters long and is developing various body parts. Only at this stage does it begin to be dependent on a rudimentary placenta. It looks a little like a segmented worm.
By the end of the fourth week, it's about 5 millimeters (about 1/5 inch) long. It's recognizable now as a vertebrate, its tube-shaped heart is beginning to beat, something like the gill arches of a fish or an amphibian become conspicuous, and there is a pronounced tail. It looks rather like a newt or a tadpole. This is the end of the first month after conception.
By the fifth week, the gross divisions of the brain can be distinguished. What will later develop into eyes are apparent, and little buds appear—on their way to becoming arms and legs.
By the sixth week, the embryo is 13 millimetres (about ½ inch) long. The eyes are still on the side of the head, as in most animals, and the reptilian face has connected slits where the mouth and nose eventually will be.
By the end of the seventh week, the tail is almost gone, and sexual characteristics can be discerned (although both sexes look female). The face is mammalian but somewhat pig-like.
By the end of the eighth week, the face resembles that of a primate but is still not quite human. Most of the human body parts are present in their essentials. Some lower brain anatomy is well-developed. The fetus shows some reflex response to delicate stimulation.
By the tenth week, the face has an unmistakably human cast. It is beginning to be possible to distinguish males from females. Nails and major bone structures are not apparent until the third month.
By the fourth month, you can tell the face of one fetus from that of another. Quickening is most commonly felt in the fifth month. The bronchioles of the lungs do not begin developing until approximately the sixth month, the alveoli still later.
So, if only a person can be murdered, when does the fetus attain personhood? When its face becomes distinctly human, near the end of the first trimester? When the fetus becomes responsive to stimuli--again, at the end of the first trimester? When it becomes active enough to be felt as quickening, typically in the middle of the second trimester? When the lungs have reached a stage of development sufficient that the fetus might, just conceivably, be able to breathe on its own in the outside air?
The trouble with these particular developmental milestones is not just that they're arbitrary. More troubling is the fact that none of them involves uniquely human characteristics--apart from the superficial matter of facial appearance.
All animals respond to stimuli and move of their own volition. Large numbers are able to breathe. But that doesn't stop us from slaughtering them by the billions. Reflexes and motion are not what make us human.
Other animals have advantages over us--in speed, strength, endurance, climbing or burrowing skills, camouflage, sight or smell or hearing, mastery of the air or water. Our one great advantage, the secret of our success, is thought--characteristically human thought. We are able to think things through, imagine events yet to occur, figure things out. That's how we invented agriculture and civilization. Thought is our blessing and our curse, and it makes us who we are.
Thinking occurs, of course, in the brain--principally in the top layers of the convoluted "gray matter" called the cerebral cortex. The roughly 100 billion neurons in the brain constitute the material basis of thought. The neurons are connected to each other, and their linkups play a major role in what we experience as thinking. But large-scale linking up of neurons doesn't begin until the 24th to 27th week of pregnancy--the sixth month.
By placing harmless electrodes on a subject's head, scientists can measure the electrical activity produced by the network of neurons inside the skull. Different kinds of mental activity show different kinds of brain waves. But brain waves with regular patterns typical of adult human brains do not appear in the fetus until about the 30th week of pregnancy--near the beginning of the third trimester. Fetuses younger than this--however alive and active they may be--lack the necessary brain architecture. They cannot yet think.
Acquiescing in the killing of any living creature, especially one that might later become a baby, is troublesome and painful. But we've rejected the extremes of "always" and "never," and this puts us--like it or not--on the slippery slope.
If we are forced to choose a developmental criterion, then this is where we draw the line: when the beginning of characteristically human thinking becomes barely possible.