Doubling Up: 7 Things You Didn’t Know About Identical Twins

Welcome to the wild world of genetics and how we sometimes get duplicates.

Hold onto your intellectual hat, because the vast mysteries of human conception and development are revealed when it comes to identical twins.

  1. Two people for the price of one (egg). Identicals are monozygotic, meaning they originate when one fertilized egg splits in two. Fraternals are dizygotic, meaning two separate eggs, separate placentas, and only 50% shared genetic material1.
  1. Identicals might share a placenta. Unlike their fraternal cousins, these twins get to share everything, including their food source in the womb, but it depends on when the egg splits. This means that the ultrasound can be misleading in determining if twins are fraternal or identical1.
  1. There is such a thing as semi-identical. Just when you thought you knew everything….a study on genetics in 2007 created a new category of twins: the semi-identical. It means that these twins share their mother’s genes identically, but only shared half the father’s genetic material. Scientists think this is the result of two sperm fertilized a single egg that then split in two. Up until 2007, we didn’t know this was possible2.
  1. Identical twins are not carbon copies of each other. It used to be a given that identicals shared 100% of their genetic material, but recent studies have indicated that might not be the case. Geneticists are hesitant to throw out numbers, but in one study, identical twins varied significantly with regard to disease susceptibility, and epigenetic factors appear to play a role3.
  1. Twins are often reported to have telepathic or extra sensory powers. It pops up often enough that twins or witnesses will experience an event where identical sibs seem to have a sixth sense. Much has been made of this phenomenon and we have our own theory that you can read about here: (insert link)
  1. Even though they are identical, twins are their own unique individuals. They have their own fingerprints, their own preferences, and their own personalities, so the old school thinking that we should treat them like copies of one person is fluff. Because they have so much in common, identicals in particular tend to be very tight, but just like any developing human, they need their own separate toys, space, and the freedom to create their own style.
  2. Identicals separated at birth share some spooky similarities. Some truly remarkable studies tracked down twins that had been separated through adoption when they were infants. These twins shared some strikingly common traits. They often did the same type of job, they bought the same brands, and they even named their pets the same names4. For more on this, check out Dr. Nancy Segal’s research:


Identical twins represent a considerable opportunity for science, but as with many of nature’s mysteries, the pursuit often only leaves us with more questions. If you are lucky enough to be blessed with identicals, you have an astoundingly cool journey ahead of you.






About Susie Almaneih

Susie Almaneih spent several years during her young adulthood teaching children dance at her church group, as well as other cultural-based activities. Susie now spends as much time as she can giving back to the families in her community. Over the years, this love for community has evolved into a deeper love for delivering positive and creative content and awareness to families of all ages.

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