which lay eggs. Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as some sharks, also bear live young.

Following experiments by French endocrinologist Alfred Jost in the 1940s, it is widely believed that the female is the default sex in mammalian sexual determination. However, this idea was called into question by a 2017 study.

Sex determination

The sex of a particular organism may be determined

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