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What is a Fraternal Twin

Updated on November 16, 2014
Fraternal twins are like two peas from the same pod.
Fraternal twins are like two peas from the same pod. | Source

The word “fraternal” can be a bit misleading. In fact, I’m a fraternal twin myself (we’re both female) and growing up I always thought the term was “ferternal.” That’s actually not even a word, but to me “fraternal” sounded like it was meant to describe twins who were boys, or maybe twins who came about because of some genetic predisposition from the father’s side of the family. While there certainly are plenty of fraternal twins who are both male, and while twins may tend to run in the father’s side of the family, the term “fraternal” is not so narrowly defined.

So what is a fraternal twin?

Essentially, a fraternal twin is one who is not identical. What exactly does that mean? Well, identical twins are basically one embryo that has split into two very early on in the development process. They not only share a nearly indistinguishable physical appearance, but the exact same blood type and genetic make-up. Fraternal twins on the other hand start off as two completely separate embryos that just happen to be developing at the same time. While many of them do indeed share similar appearances, they are no more similar genetically than non-twin siblings. They may or may not have the same blood type. That’s why fraternal twins can consist of two females, two males, or one female and one male. When it comes down to it, fraternal twins are really just siblings who happen to be the same age.

Fraternal twins are in fact the most common type of twin, comprising roughly 75% of the twin population. They are more likely to occur when the mother:

  • Is of West African descent
  • Is between the ages of 30 and 40
  • Is of greater than average height and weight
  • Has already had several previous pregnancies

However, just because you don’t fit any of the conditions listed above doesn’t mean you won’t have twins. My own mother, who is of European descent, and definitely not of greater than average height and weight, was in her mid-twenties when she had my twin sister and I. Twins don’t really even run in our family. My mom just always wanted twins, which I guess simply means to be careful what you wish for.

Interestingly, while the rate of identical twins remains constant regardless of where a person lives, and has not fluctuated throughout history, the rate of fraternal twins varies depending on geographic location and has been on the rise (according to the National Organization of Mothers of Twins Clubs). Within the United States, for example, Massachusetts and Connecticut have the highest reported proportion of twins (25% higher than the U.S. rate). Hawaii on the other hand has rate about 30 percent below the national average. Exactly why these variances occur isn’t known. Perhaps it’s just one more of the mysteries surrounding multiples.

A Few Fun Facts About Fraternal Twins

  • Roughly one-third of fraternal twins are both female, roughly one-third are both male, and roughly one-third are male-female.
  • The highest incidences of fraternal twins are found in Africa (roughly 1 in 20 births).
  • Asia has the lowest rate of fraternal twin births.
  • More fraternal twins are conceived in July than in any other month (January has the least number of fraternal twin conceptions).
  • By your fourth or fifth pregnancy, your chance of having twins is four times higher than for your first pregnancy.
  • Fraternal twins share only 50% of their DNA.
  • Fraternal twin girls have twice the chance of having twins than do singletons.

Celebrities With Fraternal Twins

  • Alanis Morissette
  • Ashton Kutcher
  • Billy Dee Williams
  • Kiefer Sutherland
  • Mario Andretti
  • Scarlett Johansson
  • Gisele Bundchen
  • Vin Diesel
  • Aaron Carter
  • Joseph Fiennes
  • Parker Posey

Are you a fraternal twin? What’s the most ridiculous question you’ve ever been asked?

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