Identical twins may look totally the same. But new research shows that identical twins aren’t so identical after all—at least not genetically.
Genes carry DNA that tells your body to make you you—hair color, height, proneness to certain diseases, everything. Until now, scientists thought identical twins must have DNA that exactly matches.
Researchers in Iceland studied DNA from 387 pairs of identical twins, along with DNA from the twins’ parents, children, and spouses. According to geneticist Kari Stefansson, they found “early mutations that separate identical twins.”
A mutation is a teeny-tiny change in a sequence of DNA—neither good nor bad. Identical twins start together as just one cell. That single cell somehow divides into two separate ones. It’s now two people! But as they grow, their cells continue to divide. Scientists found that twin DNA can change slightly during this dividing process. Some twins have up to 100 DNA differences in their cells, and some have fewer.
Of course, these differences are in only a tiny portion of each twin’s genetic code, which is why identical twins are . . . identical. But the mutation might explain why one twin grows taller or develops greater risk for certain cancers. Until now, researchers believed these kinds of differences came not from nature (genes) but from nurture (how each twin lived—what food they ate, who raised them, where they lived, and other factors).
Twins—both identical and fraternal (non-identical—fraternal twins began as two separate cells all along) have always been very valuable to science. They can help answer the old “nature versus nurture” dilemma. Twins separated at birth prove especially useful for such studies. Meet one fascinating set: “The Jim Twins.” These now-famous identical twins from Minnesota were separated as babies. Each was adopted by a different family, and both were named Jim. Later, as adults, the Jims met. They found that they didn’t just look the same. They also had lived weirdly similar lives. Each had a son. One Jim had named his son James Allan (two ls) and the other had named his son James Alan (one l). They each married a woman named Linda, divorced her, and then married a woman named Betty. Each Jim drove a blue Chevrolet, worked as a part-time sheriff, struggled with headaches, and chewed his fingernails down to the nub.
Many cases of separated twins show these surprising types of similarities. So what determines what kind of person a baby becomes—nature, or nurture? The answer, of course, is both. But the Jims show that genes may play a bigger role than people used to think. The Jims influenced science. Now science may influence the Jims—by telling them they’re not quite as similar as they thought!
What makes you you—nature, or nurture? All people are born with a sin nature. When a person is converted, he or she receives a new nature—the nature of Christ. See 2 Corinthians 5:17.