Excerpt:

People who derive more pleasure (or perhaps suffer less anxiety or discomfort) from acting as the insertive partner are referred to colloquially as “tops,” whereas those who have a clear preference for serving as the receptive partner are commonly known as “bottoms.” There are plenty of other descriptive slang terms for this gay male dichotomy as well, some repeatable (“pitchers vs. catchers,” “active vs. passive,” “dominant vs. submissive”) and others not—well, not for Scientific American , anyway.

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