New study shows influence of sisters on male sexuality

Neurobiologist David Crews has authored a paper published in the October issue of the journal Psychological Science. After studying the behavior of rats raised in particular groups, he discovered that the male rats who were raised solely with female rats were less sexually active later on than the male rats who were raised with other male rats.
Read "Deconstructing Early Life Experiences: Distinguishing the Contributions of Prenatal and Postnatal Factors to Adult Male Sexual Behavior in the Rat": Full Text, PDF
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Crews Web Page