Though researchers generally believe that sexual orientation is not determined by any one factor but by a combination of genetic, hormonal, and environmental influences, with biological factors involving a complex interplay of genetic factors and the early uterine environment, they favor biological models for the cause. They believe that sexual orientation is not a choice, and some of them believe that it is established at conception. That is, individuals do not choose to be homosexual, heterosexual, bisexual, or asexual. While current scientific investigation usually seeks to find biological explanations for the adoption of a particular sexual orientation, there are yet no replicated scientific studies supporting any specific biological etiology for sexual orientation. However, scientific studies have found a number of statistical biological differences between gay people and heterosexuals, which may result from the same underlying cause as sexual orientation itself.