A Rare Phenomenon: How Do Twins End Up With Different Skin Colours?

A Story Worth Pondering

In Britain, the Aylmer family lives a unique experience every day: twin sisters, one white and one Black, who walk down the street together only to have people assume they’re just friends. This type of twin is known scientifically as “biracial twins,” a genuinely rare phenomenon that occurs almost exclusively among families with mixed ethnic heritage.

Lucy and Maria Aylmer
Credit: Gary Roberts Photography

The Science Behind It

To understand this phenomenon, we need to look at how twins form in the first place. There are two main types:

Identical twins: These come from a single fertilized egg that splits into two. In this case, the genetic makeup is 100% identical, so it would be virtually impossible for identical twins to have noticeably different skin tones.

Fraternal (dizygotic) twins: These result from two separate eggs, each fertilized by a different sperm cell, at the same time. Each twin inherits its own unique genetic combination — much like any two siblings, except they happen to be born together.

In the case of biracial twins, the parents typically come from mixed ethnic backgrounds (for example, one parent of European descent and one of African descent). Each parent carries a mix of genes responsible for skin colour, hair, and eye colour. When fraternal twins are conceived, each embryo can inherit a different proportion of these genes — one twin might inherit mostly the genes associated with lighter traits, while the other inherits mostly those associated with darker traits.

The family pictured together when the girls were much younger
Credit: Gary Roberts Photography

Their Lives Today

Today, Lucy studies Art and Design at Gloucester College, while Maria studies Law and Psychology at Cheltenham College. They have three older siblings — George, Chynna, and Jordan — whose skin tones fall somewhere in between their two sisters’ complexions.

Lucy has said that people often ask them to prove they’re really twins, and some friends have even gone as far as asking to see their birth certificates for confirmation!

Why Is This So Rare?

Scientists estimate the odds of this happening at roughly 1 in a million twin pregnancies. This rarity comes down to a combination of factors:

Both parents need to be of mixed ethnic ancestry themselves
Each parent needs to carry a wide range of genetic variants for different traits
The genetic distribution has to fall at extreme, opposite ends between the two twins

Conclusion

This type of twinning offers a striking, real-life example of just how complex and fascinating genetics can be. Even though they were born to the same parents at the same time, these twins ended up with completely different appearances — living proof of the incredible diversity hidden within human DNA.

Source: itv.com — original story on the Aylmer twins.

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