Scientists have found more evidence suggesting sexuality is biologically determined, adding weight to arguments that homosexuality is natural.

Researchers from the Stockholm Brain Institute in Sweden, discovered that the brains of lesbians responded to known as sexual hormones differently to heterosexual women.

Volunteers were tested to see how they reacted to hormones such as female pheromones. The responses of the lesbian women involved were similar to those of straight men, while straight women were more receptive to the male hormone, the team reports in the Proceedings of the National Academy of Sciences.

Reacting to the study, Sandra Witelson, an expert on brain anatomy and sexual orientation at the Michael G. DeGroote School of Medicine at McMaster University in Ontario, Canada, told the Associated Press, “It shows sexual orientation may very well have a different basis between men and women.

“The important thing is to be open to the likely situation that there are biological factors that contribute to sexual orientation.”