After writing about identical twins (including my grandmother and her sister), I was sent this incredible story from the New York Times about two sets of identical twins in Colombia:
Two sets of identical twins were born at the same time at the same hospital. They were mixed up, with one of each being sent home with the wrong family. The two sets were raised as fraternal twins in different parts of the country. Then 25 years later, a coworker of one of the twins happened to spot his lookalike–his actual twin. All four were reunited and the mix up discovered.
Last week, I wrote about the connectedness of twins, about how my grandmother could feel that her sister had just passed. I shared about a set of identical twins from China whose story of reunification was full of coincidence. The story above, of course, exemplifies this as well. Twins give us a precious and powerful look into those connections between humans that we can’t see.
Twins also reveal truths about what makes us human on a biological level.
I had also mentioned in my previous article the work of the Minnesota Twin Family Study. I was employed there for about 18 months after graduating from the University of Minnesota. This piece above also cites the U of MN’s Twin Study while taking the opportunity to lay out plainly the debate of nature vs. nurture:
“…identical twins have helped elucidate our most basic understanding of why, and how, we become who we are. By studying the overlap of traits in fraternal twins (who share, on average, 50 percent of their genes) and the overlap of those traits in identical twins (who share 100 percent of their genes), scientists have, for more than a century, been trying to tease out how much variation within a population can be attributed to heredity and how much to environment. ‘Twins have a special claim upon our attention,’ wrote Sir Francis Galton, a British scientist who in the late 19th century was the first to compare twins who looked very much alike with those who did not (although science had not yet distinguished between identical and fraternal pairs). ‘It is, that their history affords means of distinguishing between the effects of tendencies received at birth, and those that were imposed by the special circumstances of their after lives.’
“Galton, who was Darwin’s cousin, is at least as well known for coining the term ‘eugenics’ as he is for his innovative analysis of twins (having concluded, partly from his research, that healthy, intelligent people should be given incentives to breed more). His scientific successor, Hermann Werner Siemens, a German dermatologist, in the early 1920s conducted the first studies of twins that bear remarkable similarity to those still conducted today. But he also drew conclusions that for decades contaminated the strain of research he pioneered; he supported Hitler’s arguments in favor of ‘racial hygiene.’ In seeking genetic origins for various traits they considered desirable or undesirable, these researchers seemed to be treading dangerously close to the pursuit of a master race.
“Despite periods of controversy, twins studies proliferated. Over the last 50 years, some 17,000 traits have been studied, according to a meta-analysis led by Tinca Polderman, a Dutch researcher, and Beben Benyamin, an Australian, and published this year in the journal Nature Genetics. Researchers have claimed to divine a genetic influence in such varied traits as gun ownership, voting preferences, homosexuality, job satisfaction, coffee consumption, rule enforcement and insomnia. Virtually wherever researchers have looked, they have found that identical twins’ test results are more similar than those of fraternal twins. The studies point to the influence of genes on almost every aspect of our being (a conclusion so sweeping that it indicates, to some scientists, only that the methodology must be fatally flawed). ‘Everything is heritable,’ says Eric Turkheimer, a behavioral geneticist at the University of Virginia. ‘The more genetically related a pair of people are, the more similar they are on any other outcome of interest’ — whether it be personality, TV watching or political leaning. ‘But this can be true without there being some kind of specific mechanism that is driving it, some version of a Huntington’s-disease gene. It is based on the complex combined effects of an unaccountable number of genes.’
“Arguably the most intriguing branch of twins research involves a small and unusual class of research subjects: identical twins who were reared apart. Thomas Bouchard Jr., a psychologist at the University of Minnesota, began studying them in 1979, when he first learned of Jim and Jim, two Ohio men reunited that year at age 39. They not only looked remarkably similar, but had also vacationed on the same Florida beach, married women with the same first name, divorced those women and married second wives who also shared the same name, smoked the same brand of cigarette and built miniature furniture for fun. Similar in personality as well as in vocal intonation, they seemed to have been wholly formed from conception, impervious to the effects of parenting, siblings or geography. Bouchard went on to research more than 80 identical-twin pairs reared apart, comparing them with identical twins reared together, fraternal twins reared together and fraternal twins reared apart. He found that in almost every instance, the identical twins, whether reared together or reared apart, were more similar to each other than their fraternal counterparts were for traits like personality and, more controversial, intelligence. One unexpected finding in his research suggested that the effect of a pair’s shared environment — say, their parents — had little bearing on personality. Genes and unique experiences — a semester abroad, an important friend — were more influential.
“As pure science, the study of twins reared apart has troubled some researchers. Those twins either self-select and step forward or become known to researchers through media reports — which are less inclined to cover identical twins who do not look remarkably alike, who did not marry and divorce women of the same name or choose the same obscure hobby. Identical twins who do not look remarkably alike, of course, are also less likely to be spotted and reunited in the first place. And few studies of twins, whether reared apart or reared together, have included twins from extremely different backgrounds.
‘Every study will have its critics,’ says Nancy Segal, a professor at California State University, Fullerton, who worked with Bouchard from 1982 to 1991. ‘But studying twins reared apart separates genetic and environmental effects on behavior better than any research design I know.’’’
Dr. Thomas Bouchard was a professor of mine. He used to lecture in our class precisely that which this article later states: “On average, the researchers found, any particular trait or disease in an individual is about 50 percent influenced by environment and 50 percent influenced by genes.”
He got flack for this–so did the entire U of MN psychological department. They were called Nazis because of their findings that genes matter as much as environment. Meanwhile, because of the taboo against genetic impact, the anthropology department didn’t have or receive any problems stating the scientifically inaccurate: that we’re entirely products of our environment.
There are implications and inferences when crediting genes or environment for shaping a human, but in the end, and like so many either/or arguments, the truth is that it isn’t “either/or” at all. Founding researcher of the Minnesota Twin Study, Dr. David Lykken, summed it up once by saying, “It’s not ‘nature vs. nurture’, it’s ‘nature via nurture.'”
It’s time for us to take a post-partisan position on the effects of genes and environment.
For more explanation of the science of what shapes a human being, and for the incredible tale of these four guys, take some time to read this long-form piece.