Initially they thought Koko had an ovarian tumour, which can cause mares to exhibit stallionlike behavior because of heightened levels of testosterone.
"Because these horses are from the same family line, the condition is likely a genetically heritable one," said Chenier.
"A very similar condition can occur in humans with what is known as androgen insensitivity syndrome.
This structure is composed of a pair of tentacle-bearing arms that have a circular, U-shaped, or highly coiled arrangement, depending on the species, and generates the feeding currents that these organisms use to capture prey.
These organisms generally broadcast spawn, although females of a few species take sperm into their mantle cavity, where fertilization occurs and eggs may be brooded. Brachiopods possess a distinct, free-living larval stage called a lobate larva, which have different morphologies and developmental trajectories in Although the number of living brachiopod species is relatively low compared to many other phyla, brachiopods have one of the most prolific fossil records of any organismal group, dating back to the early Cambrian Period.
Darwin's theory of sexual selection showed how such traits could be selected through competition for mates even if they were otherwise detrimental argued that sexual selection is caused by the greater ability of males than females to increase fitness by mating repeatedly, due to the females' greater energetic commitment to gametes or parental care. Sexual selection theory therefore predicts that traits increasing mating success will have evolved because they increase male success through pollen.
Here I report that a suite of floral traits of a hermaphroditic plant is best interpreted as having evolved through the male competition component of sexual selection, a result with important implications for evolutionary studies of pollination systems.
The scientists tested Koko’s relatives and found her sister Sequoia and her cousin Pandora were also intersex.
Researchers Allan King, BSc, MSc, Ph D, Tracey Chenier, DVM, DVSc, and Daniel Villagomez are the first to identify a family of horses with a rare genetic abnormality called pseudo-hermaphroditism, which causes genetically male horses to appear female on the outside.