What We’re Learning from Twins

This month’s National Geographic cover story, Twins: Alike But Not Alike by Peter Miller, which explores a newer area of scientific research called epigenetics, really got my mental wheels turning. Many of us understand that identical twins have identical DNA sequences, but even these twins are not exactly the same in real life. Some make different choices throughout their lives, such as dress and grooming, hobbies, professions, and what they study in school. Epigenetics is the study of these differences in gene expression and those factors that influence expression, as Miller explains, the result of a combined effect of both nature and nurture. A quote from his article explains it best, “‘Things written in pen you can’t change. That’s DNA,’ says geneticist Danielle Reed. ‘Things written in pencil you can. That’s epigenetics.'”

Photograph by Jodi Cobb from www.nationalgeographic.com

Over the last twelve years, I’ve been acting as a scientist making observations in my own home-made twins study (albeit without a control group). I’ve been living with a pair of fraternal twin boys of my own and observing another pair of fraternal twin girls who also got half their DNA from me when I donated my eggs to their parents. They share a lot of DNA with my boys, but are being raised in a different environment.

I can’t turn off my analytical science brain so I’ve been observing first hand which traits and habits seem to be shared between the children and thus inherited, those influenced by environment. Different than the twins in Miller’s article, our twins are not identical, they are fraternal, sharing only approximately 50% of their DNA, and no more similar to each other than any brother or sister who is not a twin.

Inheritance seems easier to identify for me. My son Tristan looks like me in his face and body type, he ended up with my anxiety, perfectionism, introversion, and academic success. Will got my creative side and love of music and science. Ruby looks like me in the face and already talks like a professor, but Raven inherited my body type, athleticism, and even my early growth rate, already surpassing mine by 2″ at 5′ 6″ in sixth grade.

Growing up, I’d wondered whether I’d inherited or learned some of these strong personality traits. Getting to know my parents as adult humans and observing these biological children as both a scientist and parent, I’ve come to conclude that more and more traits are inherited.

Miller’s article (which you can read in its entirety here) seems to confirm this conclusion. The similarities between the identical Jim Twins, born in 1939 but raised separately and then reunited in 1979 at age 39, is chilling. In addition to expected similarities like height and weight, there were a number of other amazing, yet unexplainable coincidences. Both twins were named James by their adopting families, both had a dog named Toy, both married and divorced a first wife named Linda, and a second wife named Betty. They both named a son James Alan (or Allan), both were volunteer sheriffs, were home carpenters, smoked the same cigarettes, and drank the same beer. I was dumbstruck by the simple possibility that many of the seemingly mundane choices I am making everyday might not be choices at all, but somehow dictated by my DNA.

Miller’s article highlights how far we’ve come and how far we still need to go to understand the factors that truly shape who we are. The studies he mentions of identical twins with differing expression of medical conditions like Alzheimer’s disease and autism seem dumbfounding and yet enlighten us that these conditions are influence both by genetics and environment.

If you haven’t already seen the article, do check it out. The photographs alone of identical twins by Jodi Cobb are alone reason enough.

As a parent, relative, or close friend of twins, what novice scientific observations and conclusions have you drawn about nature versus nurture?

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4 responses to “What We’re Learning from Twins

  1. Widely speaking, this is a discussion we really need to have, but it is so easily hijacked by by racists (who choose not to recognize that individual traits usually vary more than racial traits) and by do-gooders (who refuse to recognize that caring alone will not solve societal problems) that a proper investigation is unlikely.

    As long as facts are portrayed as “cold” and caring is portrayed as “warm,” we will continue to pursue impossible solutions to the wrong problems.

    Clearly genetics determine most of our tendencies. People will generally recognize the adult by knowing the infant. Hopefully, nurturing can form tendencies into productive behaviors.

  2. I loved this article. I’d like to hear more about the field of epigenetics because I feel this story is just scratching the surface.

    I also don’t like people to think their choices don’t matter and that they were determined by genes. The way I see it, even if they are determined by this, it is still true that each twin is thinking (believing) that they made their own individual (unique) choices.

    It’s one of our necessary illusions, really, to get through the day, for all of us.

    • Matthew! I think you’re right that it would be too easy to blame poor choices or behavior on our genetics, rather than taking responsibility. But we should also understand that the choices we make are influenced by factors independent of free will, factors that we still barely understand. Thanks for posting!

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