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The Scientific Accuracy of Tails' Tails

Michael Westgarth | 21 Feb 2013 17:30
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The story goes as follows: During the early 1980's a gene responsible for the correct patterning of the insect body plan was identified through a mutant fruit fly whose unusually stubby maggot offspring had bristles covering their bodies in places they would not normally grow, and thus the gene was named hedgehog. The homologous gene (i.e. gene derived from a common ancestor) in mammals and birds was discovered by a postgraduate student in 1993 who officially named it sonic hedgehog, because geneticists are gamers too (read: pokemon gene).

Given the incredible level of similarity of both embryonic developmental genes and processes between mammals, it is highly probable that the same developmental outcome could be achieved with a red fox.

Sonic hedgehog the gene codes for sonic hedgehog the protein, which is itself part of a complex series of chemical interactions involved in the embryonic development of key organs and tissues including the nervous system, spine, hands, feet, the forebrain, heart, lungs and many more. This "hedgehog" signaling pathway is present in all animals with bilateral symmetry - i.e. a top and bottom, and a front and back. Of interest to our hypothetical Tails, however, is sonic hedgehog's role in regulating the width of the mammalian face.

Embryos deficient in sonic hedgehog in what will become their face have deformed or absent ears, one single brain hemisphere and a single, gaping hole where the eyes and nose should have been; a range of fatal birth defects known as cyclopia. Conversely, a higher than normal concentration of sonic hedgehog will result in wide set eyes and broad noses while extremely high levels yield the most striking deformity of all; the front of the face splitting off into two, a disorder known as craniofacial duplication [1].

Cases of craniofacial duplication have been reported in cats, pigs and even humans. But of what interest would two faces be to a fox wanting two tails? As previously mentioned, the basis of embryonic development is conserved throughout all mammals. It stands to reason that if the complex organs found in a mammal's head can be duplicated via increased levels of embryonic sonic hedgehog, then the same or a similarly functioning protein may achieve the same result if increased at the precursor of a fox embryo's tail.

Such a phenomenon does not appear often in the scientific literature but has indeed occurred spontaneously in lab mice. A paper published in 1975 described a single mouse of a mutant strain with bent tails which had one normal and one deformed tail.

Nearly 40 years earlier it had been observed that roughly 10 percent of mice of a strain known as "Fused," which suffered from numerous deformities including missing or fused ribs and fused vertebrae, were born with an extra, smaller tail splitting off from the "main" tail. While the smaller tails were never longer than 3cm, they did contain the skeletal structure and nerves necessary, albeit deformed, for movement. Later studies showed that the gene whose mutations cause the "Fused" effect, named Axin, regulates a very early step in determining an embryo's axis in both mammals and amphibians.

Given the incredible level of similarity of both embryonic developmental genes and processes between mammals, it is highly probable that if the cause of the twin-tailed mice could be pinpointed and duplicated, the same developmental outcome could be achieved with a red fox or any other mammal.

Unfortunately for foxy Tails wannabes it is extremely unlikely that this has or ever will occur in the wild. The astronomical amount of lab rats of various strains bred by man over the years dwarfs that of the world's population of red foxes, and considering the harsh environments foxes are born into and the tendency for unhealthy cubs to be abandoned by parents, any genetic mutation that may give rise to a two-tailed fox would be swiftly eradicated by natural selection. While the natural birth of a living two-tailed fox is almost certainly possible, the probability of it having a non-fatal combination of developmental defects, and then surviving its birth, upbringing and adult life, is close to zero.

Those looking to the luxurious conditions of the test lab for a real-life Tails will also be disappointed. One of the main driving forces behind developmental biology is the fact that discoveries made with one species of mammal are likely to hold true for humans. Therefore insights into human ailments and potential treatments can be gained without invasive and unethical human experimentation. Simply put, there's little to no scientific value or gain to humanity in attempting to engineer a fox with two tails.

But so what if Yamaguchi's inspiration for Tails was originally derived from the vivid imaginations of a few ancient Japanese storytellers? It's fun to imagine. After all, with good imagination comes good questions, and with the best questions come the best answers. Now where did I put that vial of Adam ...

Michael Westgarth is a freelance writer and geneticist for hire. Discover more of his work on his blog MegaWestgarth and pick his brains through Twitter @MegaWestgarth.

[1] Information sourced from Mutants: On Genetic Variety and the Human Body by Armand Marie Leroi, 2005, Harper Perennial.

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