When you look in the mirror, your left appears as your right and your right as your left. If you were to mark a beauty spot on your right cheek, it would appear as if it is on the left, in the mirror. What if you ever met someone who was exactly like your reflection – with all the same moles, birthmarks, etc. that you have but on the opposite side? Is this possible? Can this happen?
Turns out, it can.
What Are Mirror Twins?
Mirror twins are a very special and rare kind of identical twins. In mirror twins, things work like they would between you and your mirror reflection: what’s your ‘right’ is your reflection’s ‘left’. Similarly, mirror twins show what is called ‘reverse asymmetry’.
While mirror twins look identical, their traits are in reverse asymmetry of each other... which means if one twin is a ‘lefty’, the other is a ‘righty’, if one like wearing their sack or handbag on the right shoulder, the other will wear it on the left. They may even have identical birthmarks or moles on exactly opposite sides on the body!
In extreme cases, their internal organs could also be on opposite sides. What’s more, they tend to get affected by diseases on the opposite sides too! If one twin catches an eye-infection in the right eye, the other will catch it in the left. They might even prefer being on a certain side of their parents (like when clicking pictures, or sitting down to have a meal).
Eerie... and cool too, right?
How Are Mirror Twins Formed?
Mirror twins are a kind of identical twins. Identical twins (also known as monozygotic twins) are formed when the zygote splits after formation, to give rise to two babies. This is different from non-identical twins, wherein two individual zygotes are formed, which then develop into two babies.
So what decides whether w given twin pregnancy will result in mirror twins or not? It is the moment at which the zygote splits, that determines whether your babies will be mirror twins or not.
Normally the zygote splits any time between the 4th and the 8th day after formation. At this time, the zygote is uniform, and has NOT developed a ‘left’ and ‘right’ side. However, if the zygote splits after the left-right asymmetry has already been established (between the 9th and the 12th day after formation) the result is mirror twins... who do things in exactly the opposite manner!
Cause and Symptoms of Mirror Twins
Mirror twins occur at a rate of 1 in 4 identical twins. However, the exact causes of mirror twins are not known. What predisposes a certain twin pregnancy to develop into a mirror twin pregnancy is also not known.
What is known is how
mirror twins are formed (as explained in the earlier section), but not why.
As far as symptoms go: ‘mirror twin’ is a phenomenon that may not be easily noticeable at birth unless a deep and thorough body analysis is conducted. Not every person is born with a birth-mark or a mole, so there are no physical traits that can be assuredly seen in mirror twins.
However, as the babies grow older, certain tendencies, preferences and behavioural traits may give clues to them being mirror twins: preference for a certain side while breastfeeding
, preference for a certain side of the crib, comfort while sleeping on a particular side of the parent (if co-sleeping), and so on.
Sometimes, mirror twins also ‘mimic’ each other. One waking up from his sleep may cause the other to awaken too! But this happens quite rarely.
Characteristics of Mirror Twins
Mirror twins generate a sense of wonder among family and friends, and bringing up twins
can be both amusing and frustrating at times, especially when they both need you at once! However, as they grow older, it is quite amazing to witness mirror twins interacting together, with each other and people and things around. Here are some of the things you may notice in mirror twins.
- Physical traits like birthmarks, moles, hair whorls, dimples, are on opposite sides.
- Handedness – whether a person uses the left hand or the right hand predominantly – is also typically opposite in mirror twins.
- In extreme cases, internal organs may also be asymmetric (i.e. on opposite sides). This is not a medical threat, because the entire biology of the ‘anatomically reverse’ twin is reversed, not just placement of organs. So no physiological challenges are experienced. This condition is called situs inversus.
- Behavioural traits and cognitive skills may also be complementary – one twin may be more creative and intuitive, the other more analytical and logical; one twin may be better with numbers, the other with words; and so on.
- It has also been observed that mirror twins react to diseases and infections in an asymmetric way too. For example, if both catch an eye-infection, it will be on opposite eyes; opposite body parts may be weaker/stronger and more/less susceptible to pain; teeth formation may mirror too, with one twin sprouting left teeth and the other sprouting right teeth first.
Facts about Mirror Twins
Here are some interesting facts about mirror twins.
- Mirror twins are genetically identical beings and are always the same sex too.
- Mirror twins cannot be genetically identified! Unbelievable as it may sound, the placement of birthmarks, the direction of a hair whorl (clockwise or anti-clockwise), are physical traits that cannot be ‘seen’ in a person’s genes. These are traits that need to be observed.
- The degree of ‘mirrored’-ness may vary in mirror twins. Not everything that mirror twins do will be an exact mirror image of each other.
- Some cases have been reported of the mirroring being passed to the next generation. If one of the twins has boy-children after marriage, the other may have girls. In case of siblings, the ration may be mirrored – so that one twin has 2 boys and 1 girl, while the other has 1 boy and 2 girls! However, there is no scientific backing for this, nor is there a statistical backing. It may or may not happen!
- The moment of formation of mirror twins is the last chance that the zygote has of giving rise to healthy twins! Mirror twins are formed if the zygote splits between the 9th and 12th day (since the formation of the zygote). But if the zygote splits any later than the 12th day, it gives rise to conjoined twins – also commonly referred to as Siamese twins. Conjoined twins are morphed together and cannot exist as two individual people. More often than not, they do not survive into adulthood.
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Twins in themselves are quite fascinating and evoke a sense of wonder when you behold them. Even as siblings, it is expected there will be similarities and differences... and then to meet two people who are exactly alike can be quite the experience. But if you ever meet a pair of mirror twins... it will indeed be a once in a lifetime experience!