Growth & Evolution : Polycephaly

GROWTH AND EVOLUTION : POLYCEPHALY

One of the major focuses in Teratological studies is Polycephaly. 

Polycephaly: is a condition where an animal is born with two or more heads due to a malfunction pre-birth, the term also includes Bicephaly and Tricephaly, both referring to two-headedness. Bicephalic and Tricephalic animals are only creatures in the real world that share the same process as conjoined twins, both occurences are a result of failed separation of monozygotic twins. A variation of Polycephaly is Diprosopus, which is a condition where an animal is born with two faces on a single head. Medically, these are all classed as congenital cephalic disorders.

Each head of a polycephalic animal has it's own brain, and somehow share control of the limbs, for example, American conjoined twins Brittany and Abby Hensel say that they both have control of one side of the body, one of them left side and one of them right side. Polycephalic animals poorly in the wild compared to monocephalic animals, but most occurrences happen in captivity or in domesticated animals due to inbreeding/crossbreeding.

MAMMALS WITH REPORTED POLYCEPHALY
Many cases of polycephaly have been reported all over the world, but the following animals are more frequent than others in terms of how often cases involving the species occur:

  

Cats - Numerous reports of two-faced cats have appeared over the years being relatively common, relative to reports of other polycephalic animals, however most cases die shortly after birth.
• Cattle -most cases can be found preserved in museums around the world.
• Goats and Sheep
• Pigs
• Snakes - Most polycephalic snakes have short lives but some captive individuals can live for up to 8 years. Polycephalic snakes are usually the result of inbreeding, so these cases are most often found in zoos and pet shops rather than in the wild although it is not impossible to occur naturally. The snake heads may try to attack and even attempt to swallow each other, so feeding produces a difficult challenge for the snake.
• Turtles - Two-headed turtles and tortoises are rare but not unheard of.
• Crocodiles