Freemartin
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A freemartin or free-martin (sometimes martin heifer) is an infertile cow with masculinized behavior and non-functioning ovaries.<ref>Template:MeshName</ref> Such a cow is born as one of a pair of twins, with a male calf as the other twin. Phenotypically, the animal appears female, but various aspects of her female reproductive development were altered due to acquisition of anti-Müllerian hormone from the male twin.<ref>Template:Cite journal</ref> Genetically, the animal is chimeric: karyotypy as a sample of cells shows XX/XY chromosomes. The animal originates as a female (XX), but acquires the male (XY) component in utero by exchange of some cellular material from a male twin, via vascular connections between placentas. Such cows provide an example of microchimerism.<ref name="McConico">Template:Cite journal</ref> The chimerism is mainly present in the hematopoietic stem cells.<ref>Template:Cite book</ref>
History
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Freemartins are known to have been described by the Roman writer Varro, who called them Template:Lang.<ref name="Swett">Template:Cite journal</ref>
The 18th century physician John Hunter discovered that a freemartin always has a male twin.<ref>Template:Cite journal</ref>
It was hypothesized early in the 20th century that masculinizing factors travel from the male twin to the female twin through the vascular connections of the placenta because of the vascular fusion and affect the internal anatomy of the female.<ref>Template:Cite book</ref>
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.<ref>Template:Cite journalTemplate:Verify source</ref> The discovery was made independently by American biologist Frank R. Lillie, who published it in Science in 1916.<ref>Template:Cite journal</ref> Both teams are now credited with the discovery.<ref>Template:Cite journal</ref>
In rural areas folklore often claimed this condition was not just peculiar to cattle, but extended also to human twins. This belief perpetuated for generations, as was mentioned in the writings of Cuthbert Bede.<ref>Template:Cite wikisource</ref>
Etymology
The etymology of the term "freemartin" is uncertain: speculations include that "free" may indicate "willing" (referring to the freemartin's willingness to work) or "exempt from reproduction" (referring to its sterility, or to a farmer's decision to not bother trying to breed a freemartin, or both), or that it may be derived from the Flemish word Template:Lang for a cow which gives no milk and/or has ceased to be capable of bearing offspring;<ref name=Swett/> "martin" is generally held to derive from an Irish or Gaelic word mart for "cow" or "heifer", although connections to Martinmas (when unproductive cattle were slaughtered) have also been posited.<ref name=Swett/>
Mechanism
In most cattle twins, the blood vessels in the chorions become interconnected, creating a shared circulation for both twins. If both fetuses are the same sex this is of no significance, but if they are different, male cells pass from the male twin to the female twin, where they produce hormones (testosterone and anti-Müllerian hormone) that masculinize the female twin, resulting in a freemartin.<ref>Template:Cite journal</ref> The degree of masculinization is greater if the fusion occurs earlier in the pregnancy – in about ten percent of cases no fusion takes place and the female remains fertile.<ref>Template:Cite book</ref><ref>Template:Cite book</ref>
The male twin is largely unaffected by the fusion, although the size of the testicles may be slightly reduced. Testicle size is associated with fertility, so there may be some reduction in bull fertility. Freemartins behave and grow in a similar way to castrated male cattle (steers).Template:Cn
Diagnosis
If suspected, a test can be done to detect the presence of the male Y-chromosomes in some circulating white blood cells of the subject. Genetic testing for the Y-chromosome can be performed within days of birth and can aid in the early identification of a sterile female bovine.
Physical examination of the calf may also reveal differences: a subjective assessment is that frequently there is a lengthened tuft of hair at the ventral tip of the vulva in a freemartin heifer atypical in fertile heifer calves. Also, often many (but not all) freemartins will have a shortened length of vagina compared with that of a fertile heifer. Commercial probes are available to check heifers for obvious freemartinism in lieu of doing a blood test <ref>Template:Cite journal</ref>
Other animals
A freemartin is the normal outcome of mixed twins in all cattle species which have been studied.<ref name="Peek Divers"/> It is most frequent in cattle and does not normally occur in most other mammals,<ref name="Peek Divers">Template:Cite book</ref> though it has been recorded in sheep,<ref>Template:Cite journal</ref><ref name="Youngquist"/> goats,<ref>Template:Cite journal</ref><ref name="Youngquist">Template:Cite book</ref> and pigs.<ref>Template:Cite journal</ref>
Uses
Freemartins are occasionally used in stem cell and immunology research.<ref>Template:Cite journal</ref>
Fictional use
- In the Aldous Huxley novel Brave New World, a "freemartin" (mentioned in chapters 1, 3, 11 and 17) is a woman who has been deliberately made sterile by exposure to hormones during fetal development; in the book, government policy requires freemartins to constitute 70% of the female population. A side effect of this is some freemartin women having developed beards.
- The Robert A. Heinlein novel Beyond This Horizon lists "the clever and repulsively beautiful pseudo-feminine freemartins" as one of the genetically-engineered specialist types of humans that were created in the "Empire of the Great Khans" (chapter 2).
- In the Robert Heinlein novel Farnham's Freehold, the protagonist, Hugh Farnham, is given a companion ("bedwarmer") that is described as a "natural freemartin".
- In the Avram Davidson story "The House the Blakeneys Built", the cattle are freemartins.
- In the fantasy book series Bazil Broketail by Christopher Rowley, "freemartin" is the name for a breed of sterile female dragons.
- In Footfall by Larry Niven and Jerry Pournelle, a lithely-built human woman uses the term "freemartin" to describe herself, while doubting her sexuality.
- In Nicola Griffith's novel Hild, the title character is sometimes referred to by others as a freemartin, in reference to her non-feminine character and social role.
- In Lauren Groff's novel Matrix (New York: Riverhead Books, 2021), 12th-century English peasants use freemartins to pull wagons.