• Jessica Evans

Wait... two heads?


January in today’s calendar is named after the Roman god, Janus. He’s the god of transitions, beginnings and endings, and duality. So he’s the perfect dude to introduce a new year and conclude an old one. The interesting thing about Janus is that he has two faces and looks to both the past and the future.

So, in the spirit of a new year and a fresh January – here are some cool facts about two-headed animals and humans!


Two-headedness develops while an animal is still an embryo and its affected by gravity!

In amphibians, an important collection of cells called neural crest cells are supposed to move to specific spots on the embryo at a certain point in its development.

These cells then differentiate and form different kinds of tissues, including head cartilage. They are guided by environmental cues and are sensitive to gravity.

It turns out, than when exposed to hypergravity (gravity stronger than earth’s gravity), the embryos exhibit stunted growth and two-headedness!

Flatworms can 're-grow' heads they never had

Freshwater flatworms are one of those creatures that can re-grow parts of their body if they get damaged. Sometimes, though, the poor worms get more than they bargained for!

Under rare circumstances, these flatworms grow a whole new head from a simple cut on any forward surface close enough to its head, rather than simply closing and replacing the damaged area.

At least they’ll never feel lonely again, right?

Conjoined twins

Identical twins form when an embryo splits in two, resulting in two genetically identical developing embryos. When this splitting is incomplete the result is conjoined twins – two heads or torsos joined to one body, or even two people joined by their sides.

Conjoined twins can sometimes be surgically separated, but often live fulfilling lives attached to their twin forever.

Although two-headedness is rare, it need not be something we view as freakish or ghastly. It need not be something we look upon with pity. Different doesn’t mean inferior.

In the words of Mark S. Blumberg "Earth sits alone in our solar system, a sign of life in a largely frigid wasteland. The emergence of life, then, is a rare event. But even the discovery of life beyond the perimeter of our planet, would not alter the fact that, in a universe comprising more dead space than living matter, every creature in our midst is a freak."

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©2018 by Bite-sized Sci | Jessica Evans