:::::::::Additional comment: The "genetic, hormonal, and environmental influences" matter is nature and nurture; that's why I included "or simply a complex combination of nature and nurture" after that. Whether we use many or not with regard to the nature and nurture bit, I think the nature and nurture aspect should be mentioned/linked in the lead to clarify the "genetic, hormonal, and environmental influences" aspect  how these factors work together. Also, many is referring to scientists; I take the matter that way anyway...since right before the American Psychological Association states "Many think that nature and nurture both play complex roles," they state "no findings have emerged that permit scientists to conclude that sexual orientation is determined by any particular factor or factors." I don't think that, by using the word many, the American Psychological Association was talking about average peoples' beliefs right after talking about scientists' beliefs.