The BBC Earth columnist talks about two-headed creatures that exist not only in ancient myths.
It was a blood-curdling sight. The snake-like monster, the many-headed Lernaean hydra, got out of its lair and unleashed all its rage on Hercules, the son of the Greek god Zeus, who was waiting for her.
But Hercules had a plan. He already knew that new ones were growing on the site of the severed head of Hydra, so he called his nephew Iolaus for help.
I am absolutely sure that they observed creatures with similar developmental anomalies in nature.
As soon as Hercules chopped off Hydra's head, Iolaus cauterized the wound with a torch, and new heads from this devilish creature no longer appeared.
The hydra hissed and squirmed, its poisonous blood and breath threatening death to the greatest hero of Greece, but he still prevailed.
The last head of the monster fell to the ground, and Hercules emerged victorious from this battle. Now he could begin the third of his twelve labors.
A multi-headed creature with poisonous breath and growing body parts is probably the fruit of a rich fantasy.
Promotional video:
Some authors claim that Hydra had fifty heads, while in other stories there are much fewer.
But where did such an unusual idea come from? Is it possible that the prototype of the Hydra was a multi-headed giant snake that actually existed in nature?
Scientists have been registering cases of the birth of two-headed individuals for many years. In the 1940s, researcher L. E. Cable described a double-headed needlefish embryo. He called him "tiny monster".
Many two-headed creatures have visited the laboratory of developmental biologist Arhat Abzhanov from Imperial College London.
Thanks to modern knowledge in the field of genetics, he was able to identify mutations and cellular abnormalities that could cause this phenomenon.
It is possible that such natural phenomena were the source of inspiration for the creators of ancient myths.
“I am absolutely sure that they observed creatures with similar developmental anomalies in nature and tried to somehow explain this phenomenon or reflect it in their culture,” says Abzhanov.
From time to time, two- and even three-headed individuals actually appear in the wild and in captivity. An interesting fact is that this phenomenon, known as polycephaly, occurs in various animal species.
Take the underwater world, for example. In 2013, a two-headed bovine shark embryo was discovered in the Gulf of Mexico.
The following year, the same individual was found among marine mammals: a dolphin with two heads was found on one of the Turkish beaches.
Apparently, in both cases, they were Siamese twins, developed from one egg, which after fertilization did not completely separate.
This anomaly also occurs in humans. Often, Siamese twins have not only two heads, but also a double set of internal organs and even limbs.
Thanks to his famous experiments of the early 20th century, biologist Hans Spemann was able to prove that it is possible to artificially prevent the separation of fertilized eggs and get Siamese twins.
He wanted to understand how the embryo develops. He fused two early salamander embryos using baby hairs.
He discovered that with the help of these manipulations it was possible to obtain a salamander with two heads, which fought among themselves for food, despite the fact that they had only one body. The scientist called this creature "two egoists in one body."
The list of animals, among which there are two-headed individuals, is quite large. It includes turtles, snakes, kittens and others.
We also know that such cases are characteristic not only of modern times. Paleontologists have found fossilized two-headed embryos that were millions of years old.
As Abzhanov notes, various mechanisms can serve as the reason for the appearance of numerous heads or faces.
He explains that the head as an organ is an example of convergent evolution, a process by which individuals of completely different species groups develop similar features.
Animals with and without a spine have a head, although there is no relationship between them. It seems that the head is simply a useful result of adaptation that is characteristic of many organisms.
“The head is indeed a very effective organ,” Abzhanov explains. “It’s a must for learning new surroundings.”
This is why there are so many senses on the head, including the eyes, ears, nose and mouth.
The shape of the head and the structure of the face are determined by genes, one of which is of particular importance and, in particular, is responsible for the width of the face.
It has a curious name - Sonic Hedgehog, or SHH (in honor of Sonic the hedgehog, the hero of the popular video game Sonic the Hedgehog).
It is associated with the Hedgehog (HH) family of genes, first discovered in the fruit fly. As a result of mutations of this gene, the larvae of these insects developed sharp outgrowths, similar to hedgehog needles.
Only vertebrates have SHH gene. Abzhanov explains that in the case of a weakening of the Hedgehog signaling pathway during the development of the embryo, its head gradually narrows.
In some cases, it can deform so much that a creature with one eye, similar to a Cyclops, will appear. The substance that causes such anomalies in livestock, including sheep, has received the appropriate name - cyclopamine.
It is contained in the field bindweed, which a pregnant female can accidentally eat.
What happens if the SHH signal, on the contrary, increases? This will have the opposite effect - the head will expand until two faces appear on it.
“This mutation is rare, but such cases have been recorded among both wild and domestic animals,” says Abzhanov.
Technically speaking, an individual with two faces and two heads are two different things. According to Abzhanov's observations, in order for an animal to have two separate necks and heads on the same body, another genetic error must occur at an early stage of development.
“The formation of the head, like any other part of the body, is triggered by a special group of cells at the very beginning of the development of the embryo. We call it the organizational center,”he explains.
This mechanism was discovered precisely thanks to Spemann's experiments with salamander embryos.
“If you take a group of cells and transplant them into, for example, a frog embryo, it will have two heads. This suggests that it is these cells that send the signal to the body about the need to form a head, says Abzhanov.
The same thing happens in the case of Siamese twins, but Abzhanov observed similar processes in his laboratory.
Organizing center cells can be accidentally transferred from one embryo to another by injection or incision if the surgical instruments have not been properly processed.
Scientists are trying to understand what leads to such disruptions in the development of the embryo. Abzhanov notes that one of the factors may be the ambient temperature.
Together with his colleagues, he often studies in the laboratory fertilized hen eggs that are delivered to him from farms. They noticed strange things happen in hot weather.
“The eggs we get during hot weather, when the air temperature exceeds 30C, show more anomalies, including more often two-headed embryos,” he says.
This trend is noted by other scientists as well. For example, one biologist has found that rising temperatures in water bodies can lead to the development of double-headed zebrafish embryos.
The reasons for this phenomenon have not yet been studied, however, scientists are currently conducting research to clarify the relationship between high temperature and the appearance of anomalies.
It is likely that biology was the inspiration for the authors of myths, but the opposite is also true: myths are also a source of inspiration for biologists.
In 1758, the Swedish botanist and zoologist Carl Linnaeus named a group of tiny marine creatures somewhat similar to Hydra after Hydra.
These creatures are of particular interest due to their multiple serpentine appendages and the ability to regenerate - just like the Hydra slain by Hercules.
However, it should be noted that many two-headed individuals, including Siamese twins, have very little chance of survival. They rarely go through the embryonic stage of development and almost never survive to adulthood.
As they grow and develop, individuals with two heads experience a huge burden, and scientists were once again convinced of this in 2014, when a rare specimen appeared in the laboratory of the University of Haifa in Israel - a two-headed salamander. Spemann would certainly have been delighted.
She attracted a lot of attention from the media, but was very short lived.
“Two-headed salamanders are rare,” explains Leon Blaustein, who ran the lab. "At the larval stage, everything was fine, but after the metamorphosis, the individual died."
The salamander larva is a tadpole that transforms into an adult as a result of metamorphosis, while losing gills and several fins.
His head is also undergoing significant changes. The eyes develop, the tongue and teeth appear, and the mouth becomes wider. Perhaps it was these cardinal changes that led to her early death - no one knows the answer.
Abzhanov admits that, in addition to observing real two-headed animals in nature, the Greeks could have been inspired by other phenomena. He explains that during the mating season, snakes often gather in balls.
“When you see such a sight, you can imagine that you have one snake with several heads in front of you,” he says. "It looks very scary."
Indeed, the image of the Hydra presented in the ancient drawings is very similar to the picture described above.
Polycephaly is a very unusual phenomenon that can cause fear in people - this is a feature of our psyche. This partly explains why the developmental anomaly was chosen in order to give the Hydra from ancient Greek myths a frightening look.
When faced with polycephaly, people do experience discomfort, as evidenced by the stories of Blaustein's two-headed salamander and Cable's "tiny monster".
In the first case, people even began to build conspiracy theories.
“Things started to get out of hand when various groups started claiming on the Internet that it was radiation,” Blaustein recalls. "But the reason remained unknown."
Hydra is far from the only creature with multiple heads in mythology. Performing his twelfth feat, Hercules faced the three-headed dog Cerberus.
In Japanese mythology, there is an eight-headed dragon Yamata-no Oroti, and in Slavic, there is a three-headed Serpent Gorynych.
The image of a multi-headed creature in literary works always symbolizes many dangers that cannot be easily overcome.
Thus, it can be assumed that there is a whole culture associated with the frightening effect that creatures with several heads have on people.
Much remains unclear about the phenomenon of polycephaly in animals. However, given that individuals with two heads have very little chance of surviving both in captivity and in the wild, there is no reason to assume that this feature will not remain a rare anomaly.
One can only guess where the authors of classical myths got their ideas from. It is possible that in ancient times someone saw an animal with two heads and began to tell overly embellished stories about it.
Over time, these stories could acquire more and more incredible details and eventually turn into the legends we know today.
Chris Baraniuk