These identical twins share the same genes and upbringing, but one of them is straight and the other gay. With mirror-image mannerisms and matching DNA, identical twins capture something in our imaginations. New research carried out by Dr Tuesday Watts and her team of psychologists at the University of Essex seeks to determine how and why, despite having the same upbringing and the same genes, identical twins can identify with different sexual orientations. This study found that these twins started to visibly differ from each other in this respect much later than non-twins. So could twins actually hold the key to determining the roots of our sexuality, giving us long-searched-for answers about what really makes us who we are?

A growing amount of research suggests that sexual orientation has a genetic basis. In fact, scientists recently identified two specific genes that appear to differ between gay and straight men [1]. If sexual orientation is indeed genetically determined, it would be tempting to assume that identical twins would always have the same orientation, right? If they have the exact same genes and our genes control our sexuality, this would seem like a pretty logical conclusion. Identical twins sometimes have different orientations.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Genetically identical twins can differ in their self-reported sexual orientations.

A growing amount of research suggests that sexual orientation has a genetic basis. In fact, scientists recently identified two specific genes that appear to differ between gay and straight men [1]. If sexual orientation is indeed genetically determined, it would be tempting to assume that identical twins would always have the same orientation, right? If they have the exact same genes and our genes control our sexuality, this would seem like a pretty logical conclusion.