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In developmental biology and zoology, defeminization is an aspect of the process of sexual differentiation by which a potential female-specific structure, function, or behavior is prevented from developing by one of the processes of male development. Although the term might seem to imply "removal" of female characteristics, in nearly all biological contexts it refers to prevention of an aspect of female development from manifesting.
In human biology of gender, the best known example of this is the prevention of development of the müllerian duct derivatives by anti-müllerian hormone (AMH) in the 3rd and 4th months of fetal development, though the term is not commonly used in discussions of human development.
In a number of non-human mammals, there is evidence that hormones produced by the testes act directly on the brain to prevent development of female characteristics, especially female reproductive behavior.