Scientists are hoping a new study on identical twins could shed more light on understanding human sexuality, according to a report by The Independent.
Sarah Nunn and Rosie Ablewhite are 29-year-old identical twins who have been brought up the same way in almost every way.
But there is one significant difference, Rosie is a lesbian and Sarah is straight. Boys were drawn to Rosie for being into sports and video games, while they found Sarah "boring", the report stated. But when Rosie rejected their romantic advances, they would run to Sarah.
Now, researchers at the University of Essex are using them as part of a case study to further understand why, when and how human sexuality is produced. 56 pairs of twins with "discordant sexual orientations" are part of the study, the report revealed.
For the study, researchers also examined childhood pictures of the participants. They believe gender-atypical behaviour can be spotted before puberty. In the girls’ pictures as toddlers, Sarah is seen playing with Barbie in a dress, while Rosie is wearing a Batman outfit.
The study's results showed sexuality differences can be seen at age eight in boys and six in girls. “This shows there is something early on, in the early environment, that has nothing to do with genes but can still have a tremendous effect on sexual orientation,” study author Gerulf Rieger is quoted as saying by The Independent.
However he also believes sexuality may potentially be determined before birth. “Prenatal hormones are the number one candidate,” he said. “Our theory is that even though twins are identical, what happens in the womb can be quite different. They can have different nutrition, different levels of hormones."
The study is originally published in the journal Developmental Psychology.