From the number of subspecies to the five large kingdoms that scientists have to classify living things, nature doesn’t want for diversity. Even when classifying the sexes, biological variations away from the ‘norm’, so to speak, have been recorded in both humans and animals.
In animal husbandry, cattle that are born exhibiting characteristics of both sexes are called freemartins. Freemartins are sterile female cattle that result from the twinning of a male and a female within the same uterus. This phenomenon occurs in approximately 90% of such twin pregnancies in cattle. The key reason is the exchange of blood between the male and the female foetuses during gestation.
Genetically, freemartinism is attributed to the sharing of cells carrying the Y chromosome from the male twin with the female twin. This chromosome triggers the development of male reproductive organs in the male foetus, while the female foetus, affected by the presence of male hormones, experiences incomplete development of its reproductive system. The end result is that the freemartin has an underdeveloped or non-functional reproductive tract.
In agricultural settings, because freemartins can’t reproduce, farmers often identify them through physical and/or behavioural traits to cull them from the breeding herd to improve reproductive efficiency.