  Another aspect of biology that has been used to support determinist arguments involves differences in male and female brains, and the effects of sex hormones on the expression of behavioral traits. Feminist responses in these areas primarily consist of careful analysis of studies used to support these determinist arguments. For example, Bleier (1984) points out the futility of separating nature from nurture, or in other words the structural and hormonal aspects of brain development, from social learning and environmental influences on brain development. She points out that the fetal and postnatal development of the brain is highly influenced by environmental inputs, the human brain exhibits high levels of developmental plasticity, is sensitive to experience, and finally that humans are very good at learning. It is very difficult to determine whether or not sexually dichotomized behaviors, which may be correlated with genetic, hormonal or brain differences, are fixed or changeable.