Gay, Straight, And The Reason Why by Simon LeVay

The Science of Sexual Orientation

Drawing on neuroscience, genetics, endocrinology, and psychology, this synthesis examines evidence that sexual orientation develops primarily from biological influences—especially prenatal hormones and genetic factors—rather than social learning or choice. It reviews twin studies, brain structure and function, the fraternal birth order and maternal immune effects, and animal research, weighing the strengths and limitations of each. It also situates these findings within developmental and evolutionary frameworks and considers their social and ethical implications, offering a clear overview of what science does—and does not—yet establish.

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