PRIMARY SOURCES
Bateson, Patrick. “Behavioral Development and Darwinian Evolution.” In Cycles of Contingency: Developmental Systems and Evolution, edited by Susan Oyama et al. MIT Press, 2003.
Bateson, Patrick, and Paul Martin. Design for a Life: How Biology and Psychology Shape Human Behavior. Simon & Schuster, 2001.
Downes, Stephen M. “Heredity and Heritability.” Published online on the Stanford Encyclopedia of Philosophy Web site, first posted July 15, 2004; revised May 28, 2009.
Joseph, Jay. The Gene Illusion: Genetic Research in Psychiatry and Psychology under the Microscope. Algora Publishing, 2004.
Moore, David S. The Dependent Gene: The Fallacy of “Nature vs. Nurture.” Henry Holt, 2003.
Ridley, Matt. Nature via Nurture. HarperCollins, 2003.
Turkheimer, Eric, Andreana Haley, Mary Waldron, Brian D’Onofrio, and Irving I. Gottesman. “Socioeconomic status modifies heritability of IQ in young children.” Psychological Science 14, no. 6 (November 2003): 623–28.
CHAPTER NOTES
Ted Williams retired from baseball on September 28, 1960, at age forty-two.
Standing before a grateful hometown crowd at Fenway Park and facing Baltimore’s Jack Fisher on the mound. (Full game stats available online at baseball-reference.com.)
“What if we could sell dad’s DNA and there could be little Ted Williamses all over the world?”: Farrey, “Awaiting Another Chip off Ted Williams’ Old DNA?”
Rainbow the cat and her clone Cc.
Kristen Hays writes:
Rainbow the cat is a typical calico with splotches of brown, tan and gold on white. Cc, her clone, has a striped gray coat over white. Rainbow is reserved. Cc is curious and playful. Rainbow is chunky. Cc is sleek … Sure, you can clone your favorite cat. But the copy will not necessarily act or even look like the original. (Hays, “A Year Later, Cloned Cat Is No Copycat: Cc Illustrates the Complexities of Pet Cloning.”)
“Identical genes don’t produce identical people”: Wray, Sheler, and Watson, “The World After Cloning,” pp. 59–63.
“In theory, you could create someone who would be a step ahead of other people”: Farrey, “Awaiting Another Chip off Ted Williams’ Old DNA?”
Coincidentally, they’d been given the same first name by their adoptive parents.
In fact, they had the same first name and virtually the same middle name: James Alan Lewis and James Allen Springer. These were names given separately by adopted parents, which could only reflect culture or coincidence, not genetics—but it does play to the eerie magical quality of the story.
“I thought we were going to do a single case study,” Bouchard later recalled: Wright, Twins, p.46.
“Nothing seems to me more curious,” he once wrote, “than the similarity and dissimilarity of twins”: Charles Darwin, in a letter to Francis Galton, November 7, 1875, as published on the Galton.org Web site.
Since identical twins were thought to share 100 percent of their DNA.
In fact, identical twins turn out not to have exactly the same DNA. Very close, but not exactly the same. (Anahad O’Connor, “The Claim: Identical Twins Have Identical DNA,” New York Times, March 11, 2008.)
Journalists were understandably blown away when Bouchard and colleagues published data that seemed to demonstrate that genes were responsible for roughly 60 percent of intelligence, 60 percent of personality, 40–66 percent of motor skills, 21 percent of creativity.
Intelligence
Herrnstein, Richard J., and Charles Murray. The Bell Curve. Free Press, 1994,. The authors average a number of estimates from 40–80%.
Personality
Bouchard, T. J., Jr., and Yoon-Mi Hur. “Genetic and environmental influences on the continuous scales of the Myers-Briggs type indicator: an analysis based on twins reared apart.” Journal of Personality 66, no. 2 (2008): 135.
Motor Skills
Fox, Paul W., Scott L. Hershberger, and Thomas J. Bouchard Jr. “Genetic and environmental contributions to the acquisition of a motor skill.” Nature 384 (1996): 356.
Creativity
Nichols, R. “Twin studies of ability, personality, and interests.” Homo 29 (1978): 158–73.
“Since personality is heritable …” (New York Times): Nicholas Wade, “The Twists and Turns of History, and of DNA,” New York Times, March 12, 2006.
“Men’s Fidelity Controlled by ‘Cheating Genetics’” (Drudge Report): Drudge Report, September 3, 2008.
Also: “Forty percent of [marital] infidelity [can] be blamed on genes.” (Highfield, “Unfaithful?”)
“The genetic idea has had a tumultuous passage through the twentieth century,” he wrote, “but the prevailing view of human nature at the end of the century resembles in many ways the view we had at the beginning … Circumstances do not so much dictate the outcome of a person’s life as they reflect the inner nature of the person living it. Twins have been used to prove a point, and the point is that we don’t become. We are”: Wright, Twins, p. 10.
This is really an extraordinary and very unfortunate statement. Lawrence Wright is a distinguished journalist and writer, and I am an admirer. But even great journalists and scientists can get caught up in misinterpreted science, and that’s what appears to have happened in this case.
Turkheimer found that intelligence was not 60 percent heritable, nor 40 percent, nor 20 percent, but near 0 percent.
“The models suggest,” Turkheimer wrote, “that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contributions of genes is close to zero; in affluent families, the result is almost exactly the reverse.” (Italics mine.) (Turkheimer et al., “Socioeconomic status modifies heritability of IQ in young children,” p. 632.)
“a model of [genes plus environment] is too simple”: Turkheimer et al., “Socioeconomic status modifies heritability of IQ in young children,” p. 627.
Heritability, explains author Matt Ridley, “is a population average, meaningless for any individual person”: Ridley, Nature via Nurture, p. 76.
Early shared GxE. Identical twins share a wide collection of similarities not just because they share the same genes, but because they share the same genes and early environments—hence, the same gene-environment interactions throughout gestation.
In addition to nine months of shared prenatal environment, most also have some weeks or months of shared postnatal environment before separation.
Shared cultural circumstances. In identical twins comparisons, shared biology always grabs all the attention. Inevitably overlooked is the vast number of shared cultural traits: same age, same sex, same ethnicity, and, in most cases, a raft of other shared (or very similar) social, economic, and cultural experiences.
The mere fact that two people are born on the same day can have an important impact on their subsequent behavior and beliefs. (Joseph, The Gene Illusion, p. 105.)
“All of these factors work towards increasing the resemblance of reared-apart twins,” explains psychologist Jay Joseph.
For other psychologists not to recognize their importance, he argues, is a “stunning failure.” (Joseph, The Gene Illusion, p. 100.)
To test the influence of just a few of them, psychologist W.J. Wyatt assembled fifty college students completely unrelated and unknown to one another and then placed them in random pairings purely on the basis of age and sex: Joseph, The Gene Illusion,; Wyatt, Posey, Welker, and Seamonds, “Natural levels of similarities between identical twins and between unrelated people,” p. 64.
Hidden dissimilarities. Statisticians call it “the multiple-end-point problem”: the seductive trap of selectively picking data that fit a certain thesis, while conveniently discarding the rest. For every tiny similarity between the Jim twins, there were thousands of tiny (but unmentioned) dissimilarities. “There are endless possibilities for doing bad statistical inferences,” says Stanford statistician Persi Diaconis. “You get to pick which features you want to resonate to. When you look at your mom, you might say, ‘I’m exactly the opposite.’ Someone else might say, ‘Hmm.’”
Gina Kolata adds: “And when we look at our parents, or our children, and see ourselves, it is easier than we think to get caught in the multiple-end-points statistical trap.” (Kolata, “Identity.”)
New York Times science writer Natalie Angier adds: “What the public doesn’t hear of are the many discrepancies between the twins. I know of two cases in which television producers tried to do documentaries about identical twins reared apart but then found the twins so distinctive in personal style—one talky and outgoing, the other shy and insecure—that the shows collapsed of their own unpersuasiveness”: Angier, “Separated by Birth?”
These separated-twin stories, added behavior geneticist Richard Rose, “[make] good show biz but uncertain science.” (Joseph, The Gene Illusion, p. 107.)
Jay Joseph adds:
Judith Harris has written that “there are too many of these stories for them all to be coincidences,” and it is true—they are not coincidences; they are selectively reported “show biz” combined with a stunning failure to recognize the environmental factors influencing these twins’ similar behaviors. (Joseph, The Gene Illusion, p. 107.)
Coordination and exaggeration. All twins feel a close bond with each other, and while child twins growing up together might often cling to their differences, reunited adult twins understandably revel in their similarities. Researchers try to guard against any purposeful or unwitting coordination, but in her 1981 book Identical Twins Reared Apart, Susan Farber reviewed 121 cases of twins described by researchers as “separated at birth” or “reared apart.” Only three of those pairs had actually been separated shortly after birth and studied at their first reunion.
Were these studied twins truly separate? Susan Farber reviewed 121 cases in her 1981 book Identical Twins Reared Apart—only three pairs had been truly separated shortly after birth and studied at their first reunion.
Consider also the case of Oskar Stöhr and Jack Yufe, perhaps the most compelling reunited twins ever. The identical twins were separated shortly after birth by their divorced parents, the former raised in Nazi Germany, the latter raised as a Jew in Trinidad. Despite the obvious cultural differences, their reunion at age forty-seven stunned the world with similarities: wire-rimmed glasses, mustaches, two-pocket shirts, love of spicy foods and sweet liquors, absentmindedness, habits of sleeping in front of the TV and flushing the toilet before using it. Their reported similarities were astounding indeed—until one realized that they had already been in contact for twenty-five years.
Another entertaining twosome earned the nickname “Giggle Sisters” for their constant and similar laugh. They were also both frugal, shared blue as a favorite color, drank their coffee black and cold, “squidged” up their noses, had once worked as polling clerks, and had each suffered a miscarriage with their first pregnancy. After being interviewed by researchers, though, the Giggle Sisters acknowledged inventing at least one shared life goal. (Joseph, The Gene Illusion,; Farber, Identical Twins Reared Apart, p. 100.)
Bouchard reported that the average age of his twins studied was forty, with an average of thirty years spent apart—meaning that there was an average of ten years of contact. (Wright, Twins, p. 69.)
Considering all this, was it really so shocking that Jim Lewis and Jim Springer, two thirty-nine-year-old men who shared a womb for nine months and a month more in the same hospital room, and were raised in working-class towns seventy miles apart (by parents with tastes similar enough to name their kids Jim and Larry), would end up preferring the same beer, same cigarettes, same car, same hobbies, and have some of the same habits?
Do you, reader, perhaps have a “cultural twin” out there who you’ve never met? Someone the same age from your same hometown who shares a few of your food passions, music passions, etc.? I grew up in Cincinnati, Ohio, in the 1970s. I wonder how hard it would be to find a forty-two-year-old I’ve never met from the same region who today likes Bruce Springsteen, Graeter’s ice cream, and Porsche cars, who plays the acoustic guitar, and who lost interest in baseball after Pete Rose left the Cincinnati Reds. I’d wager I could find one on the streets of Cincinnati in about three minutes. We could probably fill a baseball stadium with us …
Lest anyone think they were living perfectly parallel lives: Chen, “Twins Reared Apart.”
Otto (left) and Ewald (right).
Michael Rennie writes:
Since the sequencing of the human genome there has been an expectation that we will be able to unveil many of the secrets underlying ways in which the human body is put together, the differences that exist between individuals in muscle and bone mass and composition, and how adaptable they are to physical activity. Although there have been some successes in identifying genes that are associated with particular musculoskeletal functions, it seems that, as for many other human attributes, human body size and composition are as much a matter of environment as of natural endowment, with each having about 50% influence. The gentlemen pictured in Fig. 1 [Otto and Ewald] are in fact identical twins who chose to sculpt their bodies by different training regimes to completely different results, in order to pursue athletic careers in distance running and field events. Obviously the scope for environmental effects is large. Most of what I will discuss concerns relatively short-term effects of food and exercise, i.e. those which occur within a time frame of up to 72 h, and I am going to say very little about alterations of gene transcription, since this has not been the focus of our work until recently. Nevertheless, it did come as a surprise to me and other workers to realize that it was possible to see marked alterations in gene expression within 2 h of finishing a bout of exercise or infusing insulin; given the much slower metabolic rate of human organs compared to that of a rat or a mouse, it was to be expected that these changes would take much longer. (Rennie, “The 2004 G. L. Brown Prize Lecture,” pp. 427–28.)
Art De Vany writes:
It turns out that Otto’s more low intensity stimulation decreased ATP concentrations and activated AMP kinase. This inhibited stimulation of TSC2 so that mTOR-mediated myofibrillar stimulation did not occur. In Ewald’s case, the genes got another signal: high intensity contraction stimulated PKB activity, increasing TSC2 and activating the mTOR signal, resulting in markedly increased myofibrillar protein synthesis.
So, a low intensity signal turns on different genes and signal cascades than a high intensity signal. Low intensity—no muscle protein synthesis. High intensity—markedly increased muscle protein synthesis. Same genes, different signals, different bodies. (De Vany, “Twins.”)