Scientists have a belief that sexual orientation is not from any one factor. Instead, this is thought to be from a combination of genetics, hormones, and environment. There is more proof that supports a biological cause of sexual orientation than a social one. It is not thought that sexual orientation is a choice. Some scientists have the belief that this is set at fertilization. Statistics say there are biological differences between gay people and heterosexuals. This may result from the same cause as sexual orientation itself.