Posted: August 15, 2019
n 1856, a failed priest-botanist painted a picture in seven dimensions. It was a picture of a plant; more specifically, the mathematical nature of a plant. Capturing this plant’s nature required answering seven questions—three on color and one each on height, shape, location, and texture. Each question had only two possible answers: green or yellow, purple or white, tall or short, smooth or wrinkled, near or far, big or small.
This Cubist conceptualization of botany is the backbone of modern genetics. The multi-dimensional picture is the plant’s phenotype, its set of observable traits. Traits are controlled by genes, which come in one of two forms (alleles). Alleles combine with certain probabilities that can be calculated using neat little (Punnett) squares. Father Gregor Mendel’s avant-garde description of the pea plant is now taught as an elementary exercise in fractions.
A genetics student finds nothing shocking about this picture, just as an art student wanders past Picasso’s Les Demoiselles d’Avignon without being scandalized. Yet Mendel’s picture should dazzle and horrify. The seven features he selected seem innocuous—textures and colors of seeds and flowers and pods. Each carefully hand-selected trait, however, unlocks an additional dimension: time. These particular traits offer a vantage point from which you can watch the life of a plant unfolding, a botanical Nude Descending a Staircase.
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Just as Isaac Newton and Gottfried Leibniz’s calculus formally related an object’s present motion to its past and future motion, Mendel’s fractions formally related an organism’s present nature to its past and future nature. In some cases, there is a direct correspondence between traits and the genes which produce them. Genes hold information about a living thing’s past, its present, and the future of its offspring. The world has not yet come to terms with this branch of mathematics. “What Mendel discovered,” writes Carl Zimmer in She Has Her Mother’s Laugh, “was not a law so much as a battleground.”
The science of heredity is, indeed, a battleground, and the weapons of war have just gotten a lot more powerful. We’ve entered an era in which we can read and edit our genetic material on demand. Genomes can be sequenced and rewritten, quickly and cheaply—though not always well. This technological shift is just beginning to transform the scientific and social landscape. The ability to do good, the capacity to do evil, and the opportunity to mess things up spectacularly are all much, much greater than before. It’s an excellent time to talk about what our genetic information can and should be used for.
Journalist Zimmer’s She Has Her Mother’s Laugh and psychologist Robert Plomin’s Blueprint are both timely responses to these recent technological developments in human genetics. However, Zimmer and Plomin are two very different types of military historians.
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She Has Her Mother’s Laugh is a sprawling, intricate, at times heartrending account of the various botched and brilliant attempts to establish the laws of heredity. In the literary tradition of Barbara Tuchman’s The Guns of August (1962), Michael Shaara’s The Killer Angels (1974), or Siddhartha Mukherjee’s The Emperor of All Maladies (2010), Zimmer’s book interweaves stories of the individuals who have fought and are still fighting the battle—from scientists, soldiers, and statesmen to patients, physicians, and parents.
The biological actors get their own narratives as well—cells and chromosomes become compelling characters. Zimmer’s best moment in this respect comes when explaining the “laughably baroque” process of certain cell divisions. When a cell divides, it performs a miracle akin to Jesus feeding the multitude: from one cell with one set of genetic material arise two. The elaborate cellular square-dance by which DNA is replicated, packaged, and distributed into two new cells is known as mitosis. However, sometimes cells orchestrate an even stranger courting dance—meiosis. In this scenario, the original cell doubles once but divides twice. The resulting cells are left impotent, with only half the genetic material needed to function properly.
As a young biology student, I was catastrophically confused about the difference between mitosis and meiosis. Zimmer’s book made me feel considerably better about this confusion: “The biologist Laurence Hurst once wrote that meiosis takes place ‘in a manner reminiscent of drunkards returning from an evening’s revelry: one step backwards, two steps forward.’” Zimmer transforms the clumsy footwork, enumerating how “this strange stumbling is also responsible for heredity’s most elegant patterns.”
Living things pass on genetic information to their descendants—but ‘descendant’ means a different thing to different creatures. Viruses have genetic material, but cannot make more of themselves directly. They must infect another cell to replicate: “When it comes to viruses, heredity is almost an abstraction. They have no material bond to their ancestors, since all the atoms in a new virus come from the host cell where it formed.” Bacteria have a slightly different family situation—they can make more bacteria, but, in so doing, they cease to be. “For microbes…their ancestors vanish.” When a bacterial cell divides, it destroys itself, splitting into two new bacteria.
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Cells in our bodies regularly undergo the same mitotic divisions as bacteria, doubling and splitting to make two new cells. Certain cells, however, undergo meiosis, making seemingly incomplete “germ cells”—better known as eggs and sperm. The extra fission event gives these cells the ability to later fuse, forming a new cell with a genetic identity distinct from either of its ancestors. The apparent stinginess of meiosis, the petulant refusal to share all of one’s genetic material, makes it possible for us to raise our children rather than become them. Because of this process of non-destructive replication, “[w]e humans can have the opportunity to get to know our parents.”
Zimmer’s book leaves the reader reeling from the cleverness and complexity of biological systems. Our bodies are mosaics and chimeras—different cells contain different genomes. Even cells with identical genomes can suppress their genetic nature—through epigenetic espionage or chromosomal silencing. The environment—especially early life exposure to toxins, starvation, or stress—can determine which of our genes see the light of day. There are more things in the laws of heredity than were dreamt of in Mendel’s philosophy.
We now know that Mendel’s math works only when there is a direct correspondence between a gene and a trait. Mendel selected situations in which the relationship between the two could be measured, understood, and ultimately predicted using simple fractions. In humans, there are certain diseases which can be traced back to a specific gene: cystic fibrosis, hemophilia, and Huntington’s disease among them. Very few human “traits,” however, map directly onto a single gene. There is no one gene for height or weight, sense of humor or attractiveness, athleticism, creativity, intelligence, or anything else you might put on a dating profile. Mendel’s mathematics was a brilliant first approximation, but the reality of the situation is far more complex—in peas and people.
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If a nuanced, literary approach to the complex science of human heredity isn’t your style, Plomin’s Blueprint might be right up your alley. Blueprint is a self-admitted “sales pitch about a new fortune-telling device that promises to transform our understanding of ourselves and our life trajectories.” The author promises “a novel perspective on equal opportunity, social mobility and the structure of society” based on the findings of behavioral genetics. Sadly, there is nothing novel here. The book is a rambling, entirely predictable rebranding of determinism with a few charts, numbers, and DNA base pairs thrown in.
Plomin has made a career of looking at siblings—in particular, twins. “[T]wins are a biological experiment,” he says, “a gift to science.” Twins are grown by the same scientist (the mother), at the same time, under the same conditions, within the same environment. Identical twins have the same genes; fraternal twins do not. If twins are raised apart—something which evidently happens often enough to power a career—the role of the parent can be removed from the “experiment,” allowing one to distinguish between nature (genes) and nurture (environment).
By studying twins reared together or apart, Plomin has found that genetically similar people are similar in other respects. If your twin is tall, you are more likely to be tall. If your twin is a bad student, you are more likely to be a bad student. If your twin develops Alzheimer’s, you are more likely to develop Alzheimer’s. Genes matter, for anyone who hasn’t been paying attention for the last century or so.
Plomin wants you to believe he can look at your DNA, use some high-school statistics to calculate your “polygenic score,” and thereby “tell [y]our genetic fortunes.” This assertion is, at best, naïve and, at worst, deliberately misleading. By far the best chapter in the book, “Gene-hunting,” is a history of the failed attempts to find the genes that explain the mind. Even armed with a complete knowledge of every single base pair in your genome, we cannot (yet) tell you exactly how your body and mind will behave. Because this wouldn’t sell books, Blueprint is based entirely on ‘heritability,’ a statistic with which Plomin bludgeons the reader. Heritability relates genes to traits numerically in a way that refuses to answer the question everyone wants answered.
In statistics, data are often described using two measurements: one capturing magnitude, one messiness. A group of people might be on average five feet tall (magnitude) plus or minus a couple inches (messiness). A reasonable person would ask how genes correspond to height’s magnitude. ‘Heritability’ does not relate genes to the trait’s magnitude; it relates the trait’s messiness to the messiness of genes. It is a number which estimates what’s left for genes to do once the environment and random chance have taken their toll. A trait (e.g., height) can be highly heritable, but that doesn’t mean we can look at your genes and tell you how tall you’ll become. Without such predictive power, this statistic is effectively useless. If you want to make sure a child grows up to be short, starve them. No need to bring genetics into this.
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For the most part, genetics doesn’t enter Blueprint. DNA gets its first formal introduction on page 109, accompanied by an apology “if this chapter occasionally seems like a biology lesson.” As a biologist, I can tell you, it does not. Within ten furious pages, Plomin mangles the history of genetics, blows past the ethics of CRISPR gene-editing technologies, uses a discussion of polymorphisms to set up a fat joke, and makes the book’s first and only passing reference to the major genetic interface between nature and nurture (in parentheses).
Throughout, he persistently overlooks or obscures the interesting and important relationships among genes, the environment, and human experience. The environment can alter our traits without altering our genes, and these alterations can be passed on to descendants. It’s a fascinating phenomenon called epigenetics, though you will not find it in the index. In Blueprint, a self-described behavioral geneticist spends 200 pages bulldozing a path from genes to heritable human traits without acknowledging the biological mechanisms of circumventing this route. This is also a fascinating phenomenon.
Blueprint suffers from a lack of mathematical, genetic, or neuroscientific sophistication which makes it hard to take seriously from any scientific perspective. From a lifetime of work, Plomin has concluded that identical twins are more identical than non-identical twins and other siblings. Now, his “goal is to tell the truth as I see it, without pulling punches for the sake of perceived political correctness.” That truth boils down to “genetic essentialism,” the notion that we have certain essential characteristics that make us us, that these characteristics can be found in our DNA, and that there’s nothing we can do about it—so we might as well accept it and move on. Plomin is then off to the races, dismissing the roles of parents, schools, the environment, traumatic life events, and whatever else is on hand.
He intends to provoke. This is an issue, however, where no provocation is needed. In the history of human genetics, the main theater of war is well-established: the Intelligence Front. The battle to establish a biological basis for human intelligence, by any means necessary, is far older than genetics itself. Blueprint is an important reminder that all is not quiet on this front. As we all know, correlation does not imply causation. But Plomin has built a career on correlations. He should know better than anyone there’s a suspicious association between the tendency to perpetrate industrial-scale atrocities and the tendency to misrepresent the heritability of human minds.
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Almost all the arguments in Blueprint are well known, predating gene sequencing, big data, brain imaging, and behavioral genetics. The arguments can be and have been dismissed using op-eds, speeches, and studies written a century ago, many of which are outlined in Zimmer’s book. The American eugenics movement of the early 20th century was characterized by precisely the same combination of statistical dishonesty, shoddy science, and lack of social nuance. Most of the arguments in Blueprint would simply be laughable—except eugenics isn’t all that funny.
Neither Blueprint nor She Has Her Mother’s Laugh will make you a card-carrying geneticist, just as no military history can make you a soldier or general. The books will, however, lead to vastly different conversations at dinner parties on society’s best strategy now that the weapons of genetic war have gotten more dangerous.
Blueprint may lead you to conclude that behavioral genetics is the most recent rebranding of the eugenics movement, or that some of its practitioners are, at best, woefully naïve about their own ancestral origins. Regardless, you’ll emerge with the conviction that we should teach people history, genetics, and math properly.
She Has Her Mother’s Laugh will provide you with an endless series of anecdotes with which to regale dinner guests. You will find stories to prove that scientists are idiots and also geniuses, that they give up too quickly and are too stuck in their ways, that they are ushering in the apocalypse and that they are our only hope.
I can tell you what these books contain, but I cannot tell you how your dinner conversation will unfold. Similarly, a geneticist can tell you the contents of your genome, but not how your life will unfold. The mathematics of heredity does not predict which genes inevitably lead to which human realities, because human realities are shaped by more than genes.
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DNA is not a blueprint. A blueprint faithfully maps out each part of an envisioned structure. Unlike a battleship or a building, our bodies and minds are not static structures constructed to specification. Identical twins may have identical genomes, but they are not the same person, they do not have the same minds, and they will not live the same life, regardless of whether they are ripped from each other.
It is more appropriate to think of DNA as the military-industrial complex of a cell or an organism. Your DNA is the arsenal of tactics, strategies, industries, weapons, and resources accumulated by your ancestors as they struggled to survive against random chance and a hostile, unpredictable environment. Regardless of how they went about doing it, every one of your ancestors managed to survive just long enough to produce you. You have inherited a unique set of capabilities, cobbled together within and across lifetimes, based on past experiences which may or may not be relevant to you now. Your ancestors did not give you a blueprint from which to build the ship they envisioned. They gave you the ability to draw your own blueprint and build the ship you envision.
Just like any weapon or resource, you will use your genetic arsenal as you see fit, based on the circumstances in which you find yourself. I’m sure your ancestors would be fascinated to see what you do with the tools they’ve provided. But they didn’t know what you would encounter. They didn’t know what you might need. The world in which they lived is not the one in which you live. Heredity, the American botanist Luther Burbank once declared, “is only the sum of all past environments.” For now, the future is still up to us.