Is There Really Such a Thing as the Evil Twin?

Posted on September 29, 2014


Lila has known several sets of twins over the years. Last weekend, I had occasion to renew the acquaintance of a set I have known for several decades now.

Nothing has changed: one twin is kindhearted and thoughtful, and the other is… well… kind of a jerk.

How could twins be so different from each other? I wondered this years ago, and I wondered again over the past day or two. Now I am wondering: is this set of twins a mirror-image set?

Mirroring of twins occurs in about 25% of cases of identical twins, and results from a somewhat later splitting of the fertilized ovum into two separate embryos. One might think that the mirroring is purely physical… maybe one twin has a slightly larger right eye, while the other has a slightly larger left eye; maybe one twin has a mole on the left shoulder, the other has the same mole on the right shoulder. Mirror-image twins may even have medical conditions that show up on opposite sides of their bodies.

But the mirror-imaging is not just superficial or physical; this mirroring also applies to such things as sleep patterns, sexual orientation, psychology, and which hand is dominant.

Or… one twin might be a nice thoughtful person, and the other might be a jerk. I wonder if this is because of mirroring of some deep internal brain structures, something little-understood that drives the formation of the personality on a basic, fundamental level. These particular twins were raised together, so I can’t really see how their environment or upbringing could result in two such different personalities.

Are twins such as these the inspiration for Bizarro World, and any number of fictional “evil twin” stories? What do you think?