Zak, right, and Wheezie is a rare two-headed bearded dragon owned by Barbara and Frank Witte of Fowler, California.

Strange though it may seem, two-headed animals have been documented among many different species, although most tend to fall within the realm of turtles, snakes, and traditional livestock animals such as cows, sheep, and pigs. 

While their appearance can certainly be shocking, the cause of their bicephalic bodies is nothing more than genetic mutation and cellular displacements, as the BBC writes.

When you see a two-headed, or polycephalic, animal, you’re actually looking at a set of twins that failed to separate after fertilization. This can result in the conjoining of twins when a gene known as “sonic hedgehog” or “SHH” is increased during embryonic development, which can cause the head or face to widen, often resulting in two faces. When a group of cells known as organizers becomes triggered, two entirely separate heads can form, resulting in individual necks stemming from a single body.

So, what causes such genetic abnormalities? Depending on the species, there is a wide range of proposed explanations.

When it comes to sharks, for example, of which there have been many mutations witnessed, researchers look to a variety of possible factorsranging from metabolic disorders and infection to pollution or overfishing, the latter of which can lead to a limited gene pool resulting in physical abnormalities. Some also blame rising water temperatures, although research is still being conducted in an effort to truly understand how these changes might affect genetics.

Despite the recent influx of two-headed marine life being reported, polycephalic animals are believed to have been around since the early days of human civilization, perhaps inspiring ancient myths and tales that tell of multi-headed beasts slain by heroic protagonists of their time.

However, many of these two-headed animals don’t live beyond the embryonic stage, and those that do survive birth typically don’t make it more than a few weeks or months, though there are exceptions to the rule.

A two-headed turtle found at a market in China. Its new owner noted that it is in good health and eats more than normal one-headed turtles. March 14, 2006.
Owners feed milk to a two-headed cattle cub with four eyes and two mouths in Lanzhou, China. February 5, 2007.
Zak, right, and Wheezie is a rare two-headed bearded dragon owned by Barbara and Frank Witte of Fowler, California.
A Palestinian farmer holds a two-headed sheep outside his family home in the West Bank al-Fawar refugee camp, near Hebron. November 9, 2008.
A two-headed bobtail lizard living in Perth, Australia eats from both heads but the larger head has also tried to attack the smaller one, and its movement is difficult as both heads control its back legs. April 22, 2010.
A two-headed calf, named Sana Saida (“Happy New Year” in Arabic) is seen in the Moroccan village of Sefrou. January 3, 2014.
A two-headed rattle snake in its terrarium in the zoo in Scheidegg, Germany. July 22, 2016.

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