Animal sexual behaviour however, is proving to be false as, "most hormones don’t influence behaviour directly. Rather, they affect thinking and emotions in variable ways (Azar, 40)." There is much more involved in sexual behaviour in the mammalian animal than oxytocin and vasopressin can explain. It is often assumed that animals do not have sex for pleasure, or alternatively that humans, pigs, bonoboes (and perhaps dolphins and one or two more species of primates) are the only species that do. This is sometimes stated as "animals mate only for reproduction". This view is considered a misconception by some scholars. Jonathan Balcombe argues that
Sex differences in humans genital and breast differentiation, and differentiation of muscle mass, height, and hair distribution. There are also differences in the structure of specific areas of the brain. For example, on average, the SDN (INAH3 in humans) has been repeatedly found to be considerably larger in males than in females. Research on biological sex differences in human psychology investigates cognitive and behavioral differences between men and women. This research employs experimental tests of cognition, which take a variety of forms. Tests focus on possible differences in areas such as IQ, spatial reasoning, aggression, emotion, and brain structure and function. Chromosomal make up