For the first time, an external factor turns a male mammal into a female

An experiment in mice has discovered that a mother’s iron deficiency alters sex determination. Until now, it was believed that only genetics defined this biological trait

NOTE: The researchers rightly point out that the findings might not apply to people at all.

BUT... it is an important clue that genetics alone don't determine sex at birth. And while the focus is (inevitably) on genitalia, there is some acknowledgment that other aspects of sexual development might be affected as well. Possibly, I wonder, the brain. Where our own understanding of our sexual selves resides.