Why identical twins grow apart

There is something really special about identical twins, or monozygote twins as they're also called. Every human being is unique, with its own genetic makeup. But identical twins share the same DNA: the same person in two bodies. That also explains why identical twins always share the same gender.

Their identical DNA makes them very valuable for science. Because their genetic makeup is identical, everything that differs between the twins must be caused by the environment. Twins that are brought up in the same family experience identical macro environments (same family, neighbourhood, school, etc.) but different micro environments (possibly different placentas in the womb, different relationships with familymembers, different school friends, etc). Which could explain subtle differences between identical twins. But then there are twins that are split up and brought up in totally different environments. There are twins that were adopted together that are raised in the same macro environments but not by their biological family. The possibilities are endless.
All these different situations can provide us with interesting information about what contributes to what in the development.

Identical twins have a special place in my heart, not just because it's a fascinating concept but because my grandmother is an identical twin. And that's something you don't hear everyday.

No matter how identical, monozygote twins usually aren't as identical on the inside as they appear on the outside. And as they grow older they start to show more differences on the outside as well. How is this possible?

As said the environment influences the development, causing differences in identical twins. One way in which this happens is by turning certain genes on and others off in the genetic makeup. This phenomenon is called epigenetics. Certain foods for example are believed to turn certain genes on or off, causing the same DNA to produce different outcomes in identical twins. This can explain why twins living in the same environment differ from one another on certain aspects.

As people get older the environment becomes more important than their genetic makeup. This, in combination with epigenetics, explains why identical twins usually show more differences in appearance as they grow older. Since, apart from a greater influence of environment over DNA, the twins will move out of their family home and they will create their own family. They will usually live further apart from each other, in separate households, surrounded by different people, experiencing different experiences, giving different environmental factors free gein. As the twins get shaped by different environments they move further away from their identical sibling.

The first picture at the top of this blog shows my grandmother and her twin sister along with their older sister in the 1940s. She honestly can't remember if she's standing on the right or left in this picture. I can't tell either.
The second picture is from a few years ago.

Can you tell them apart now? ;)

Hope you enjoyed this little insight into the magical world of twins. Follow me for more science, travel adventures, and days out of the life of a tiny, fluffy dog.

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