Ancon sheep
Short-legged sheep used by Darwin to argue against blending inheritance.
The Ancon sheep, also known as "Otter" sheep, were a type of domestic sheep with elongated bodies and notably short, crooked forelegs. The name most often refers to a line descended from a single lamb born in 1791 in Massachusetts. Breeders artificially selected and maintained these sheep because their short legs made them unable to jump fences, a useful trait. When this trait was no longer needed, the breed was allowed to die out in 1876. The term "Ancon" has also been used for other sheep strains with the same physical appearance, including a Norwegian line from a single lamb born in 1919 and a Texan line from a single lamb born in 1962. Scientists allowed these lineages to go extinct after they were no longer needed for genetic research. Archaeological digs in Leicester, UK, have uncovered foot bones—metacarpals, metatarsals, and phalanges—matching Ancon sheep and dating to around AD 1500, showing the same condition appeared independently at least four times. The distinctive features result from a recessive dwarf mutation that causes chondrodystrophy and often leads to crippling.
Despite their small numbers, Ancon sheep played a notable role in biology. Charles Darwin referenced them several times in *On the Origin of Species* to support his argument that offspring inherit separate traits from each parent, rather than a blend of parental traits. If blending were true, a cross between an Ancon and a common sheep would produce offspring of intermediate height. Instead, the offspring were either fully Ancon or fully common, backing Darwin’s view. Darwin called the Ancon a "sport"—a new form appearing suddenly from a prior species, as opposed to one arising gradually through natural selection of many small traits. He argued in his 1868 work *The Variation of Animals and Plants Under Domestication* that such sudden mutations are rare or nonexistent in the wild, occurring mainly in captivity. Later supporters of Darwin noted that the Ancon sheep differed from its ancestors by essentially a single trait—short legs—making a rapid mutation unusually likely, since most species and breeds differ from their ancestors by many traits.
Quick Facts
- Country
- United States
- Woolcolor
- White
- Maleweight
- 45 lb
- Note
- Dwarf
Facts from the source article.
Lore & Background
The Ancon sheep lineage began with a single affected lamb born in 1791 in Massachusetts, USA. Breeders artificially selected and maintained these sheep for their desirable inability to jump over fences. The breed was allowed to go extinct in 1876 when it was no longer required. Similar strains arose independently: a Norwegian stock from a single individual born in 1919, and a Texan stock from a single individual born in 1962; both were allowed to go extinct after scientists no longer needed them for genetic research. Archaeological excavations in Leicester, UK have revealed metacarpals, metatarsals and phalanges characteristic of Ancon sheep dating to approximately AD 1500, showing the phenotype arose independently at least four times. The unique features are caused by a recessive dwarf mutation that often results in crippling, specifically chondrodystrophy.
Reader's Guide
Despite the Ancon's small numbers, its contribution to the history of biology has been substantial. Several chapters in Charles Darwin's On the Origin of Species refer to the Ancon as an example of his argument that offspring inherit independent characteristics from their parents. This notion denounces the long-held belief among naturalists and breeders that inherited traits were a 'blending' of the traits of each parent. If blending were true, the offspring of an Ancon and a common sheep would have a height between those of the parents; instead, the resulting offspring were either Ancon or common, thus supporting Darwin's contention. Darwin referred to the Ancon as a 'sport', or a new species or breed born suddenly from a prior species, as opposed to a new species developing gradually through natural selection of multiple traits. In his 1868 work The Variation of Animals and Plants Under Domestication, Darwin argued that sudden mutations such as the Ancon are rare to non-existent outside of captivity. Later scholars supporting Darwin's view pointed out that the Ancon sheep had essentially a single trait—their short legs—which also made rapid mutation unusually likely, since other species and breeds are set apart from their progenitors by many traits.
Did You Know?
- The Ancon sheep's short legs were caused by a recessive dwarf mutation resulting in chondrodystrophy, which often led to crippling.
- The first Ancon lineage was bred for its inability to jump fences and was allowed to go extinct in 1876 when it was no longer required.
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