Overall, as many as 12% of human pregnancies may start as multiple pregnancies, but under 2% carry to term, resulting in a vanishing twin.
To think that a new science book can contribute positively to the hot-again issue of abortion regulation in the United States is likely wishful thinking. Science is often portrayed the enemy here, as it has also become in the Covid-19 mitigation “debate” (hell, more like an inane insurrection at your local school board meeting). Long-time science communicator Carl Zimmer’s newest book is titled Life’s Edge: The Search for What it Means to Be Alive (Dutton, 2021), and while the above quote does not come from his book, Zimmer does address the “twin dilemma” in trying to reason out “when life begins” in the abortion debate.
As a hard-core left-hander myself, I have long been fascinated with a theory, which had fallen on hard times but may have new life, that many left-handers are one half of a “vanishing twin” pair, as twinning at a certain point of development often results in one right-handed and one left-handed child. Independent of handedness but noting the larger-than-expected frequency of twinning, these Dutch researchers claim an 80% accuracy in detecting twins from an “epigenetic signature,” even if they are the surviving half of a twin pair. When 23andMe adds this test, perhaps I will break down and share my DNA with them.
How many chromosomes?
Author Carl Zimmer does not get too deep into theological questions in his book about the different things we mean when we say that something is “living.” However, in an early chapter he does lay out the rather extended timeline of how a unique on-track fetus emerges from a fertilized ovum. It is much more complicated than “Boom! A Person!” Rather, the emergence of life is more of a continuum and a probability distribution of success, starting from the point when one of millions of your father’s sperm “wins the lottery” by entering an egg, and on to something “living” that resembles a fetus in process.
Initially it is not even as simple as the common portrayal of 23 of your mother’s chromosomes merging with 23 of your father’s. Rather, the fertilized ovum initially contains all 46 of your mother’s chromosomes plus your father’s half, for a total of 69 initial chromosomes that need to be whittled down in those first few days. And that process is sometimes not successful, resulting in numerous forms of non-standard DNA sets, such as the extra chromosome that results in Down Syndrome.
The initial protein processing in your emerging zygote-self carries over from your mother as well, requiring what are ominously called “assassin proteins” which pare the set down eventually to your final mix of DNA-dependent proteins from both parents. And then begins the float down toward implantation in the uterus, sometimes successfully but often-times not. Zimmer cites a number, from a 2016 study, of between 10 percent and 40 percent of fertilized, in-process zygotes that never successfully implant. If I may insert theological language, these are “God’s natural abortions,” which are legion. That, in my view is “Theology Hurdle #1” in the abortion debate.
The twin dilemma
“Theology Hurdle #2” is what I term the “twin dilemma.” It may take identical (monozygotic) twins up to eight days (and even up to twelve days in the case of conjoined twins) to emerge from one fertilized zygote. Using religious language again, how many “human souls” existed during that first week “after conception”? One or two? And if that 10% “vanishing twin” number is anywhere near correct, then what is the theology at work here? Comment and explain, please; I really want to know. What happened to my (possible) right-handed twin brother?
Note that, while the most common hormonal birth control methods act by preventing ovulation, they also have a secondary effect of making the uterus less likely to allow a successful implantation of a fertilized zygote. This is why the most hardline opponents of doctor-assisted or hormonally-induced abortion also oppose almost all forms of contraception. The logical hurdles get tricky here.
And to complicate the dilemma even more, Zimmer cites the much rarer, but no less real, human chimeras, who are a mix of two distinct sets of DNA in different organs of the body. The theology of that one gets fun as well.
But that’s a small part of the book
Gosh, I got off track. Zimmer’s engaging book looks at “life” from many more angles, starting with the most basic plant and animal life. Most people have never heard of tartigrades and rotifers, animal forms which can be completely desiccated and “dead” by most criteria for many years, and even spend time in outer space, but can be “revived” (from the Latin “in vivo”) simply by adding water. The line between “dead” and “alive” can get pretty thin.
A fascinating chapter on slime molds illustrates yet another form of life that, even without a brain, seems to “intelligently” go to maze-solving-like lengths to find both nourishment and “attractive” new slime mold DNA with which to (sort of) procreate. Perhaps we overestimate the complexity of most of our daily human existence, which is pretty much these two tasks.
And on the dying side, there is a continuum in the cessation of life also. Zimmer explores the history of the discovery of “the vital tripod,” the combination of the active brain, heart, and lungs that are all required to be functional for humans to be considered “alive.” That story of determining when you legally die has been a convoluted one, and on the edges, we still have not figured it all out. Most hospital deaths today have a very arbitrary “pronouncement” of death by a doctor in authority, even though we have created a “new limbo” in which we can often keep one or two parts of that “vital tripod” functioning for perhaps years.
Theology meets biology meets public policy in determining this point of our eventual “termination.” As the Covid crisis has prematurely moved forward that end-of-life point in so many thousands of people in recent months (and since the availability of the vaccine, proportionately more science deniers), researchers from Mount Sinai Hospital in New York have uncovered “biomarkers” in the heart activity of Covid-19 patients that strongly “predict death” several days out. Ponder those implications a bit. I’ll wait…
Almost 3000 years ago the Greek poet Hesiod described Atropos, the third Fate who arbitrarily “cuts the thread” of each human life. As I have monitored for over a year the data of the nation’s Covid-19 infections and deaths, it appears to me that we are perhaps learning that our own “end point” is more like a probability function than a single event. And with the odds perhaps even changing depending on whom you voted for in the 2020 Presidential election. Some might find that more comforting than others.
Every life’s a story
The first Greek Fate, named Clotho, spins the unique thread of life for each of us, akin to our personal DNA starting point. Lachesis, the second fate, “weaves the cloth” of our lives using that thread, as we individually encounter epigenetic body changes, strange coronaviruses, and life’s crossroads along the way. The third Fate sends over a drunk driver to run you down while jogging, or a TV presenter to convince you to ingest horse-drench. Each chapter in Carl Zimmer’s Life’s Edge takes us to an interesting science laboratory, or alternatively on a trip back in time to tell of a scientist that I had never heard of. The common “thread” in the story is this very fuzzy (and sometimes slimy) line we are all riding between “not-life” and “life.”