A freemartin or free-martin (sometimes martin heifer) is an infertile female mammal which has masculinized behavior and non-functioning ovaries. Genetically and externally the animal is female, but it is sterilized in the womb by hormones from a male twin, becoming an infertile partial intersex. Freemartinism is the normal outcome of mixed-sex twins in all cattle species that have been studied, and it also occurs occasionally in other mammals inc...
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A freemartin or free-martin (sometimes martin heifer) is an infertile female mammal which has masculinized behavior and non-functioning ovaries. Genetically and externally the animal is female, but it is sterilized in the womb by hormones from a male twin, becoming an infertile partial intersex. Freemartinism is the normal outcome of mixed-sex twins in all cattle species that have been studied, and it also occurs occasionally in other mammals including sheep, goats and pigs.
The 18th-century physician John Hunter discovered that a freemartin always has a male twin.
Several researchers made the discovery that a freemartin results when a female fetus has its chorion fuse in the uterus with that of a male twin. The result was published in 1916 by Tandler and Keller. The discovery was made independently by American biologist Frank R. Lillie, who published it in Science in 1916. Both teams are now credited with the discovery.
In rural areas folklore often claimed this condition was not...
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