When this photo arrived on the internet in 2011 many were quick to dismiss it as fake. Rather than Photoshop, this shark foetus can attribute its single eye to a birth defect.
When a pregnant dusky shark was caught in the Gulf of California in 2011, fishermen found quite a surprise. Alongside 9 normal pups was a white pup with a single large eye. Other abnormalities were also noticed – the pup had no pigment, no nostrils, a bump on its snout and deformed tail and spine. It’s very doubtful the pup would have survived outside the womb.
This defect is named cyclopia, after the one-eyed giants of Greek myths, and most cases of it are due to a disorder known as holoprosencephaly (HPE). In early foetal development the forebrain – which begins development as a single lobe – splits into the two cerebral hemispheres. When this fails to happen properly the result is holoprosencephaly (“holo” – whole, “prosencephalon” – forebrain).
There are varying degrees of HPE and severity has a huge effect of life expectancy. Radical facial deformities such as cyclopia appear with the most severe forms – as a general guide, the worse the deformities, the greater the severity and the lower the life expectancy. Creatures with a very severe form of HPE have a life expectancy of less than a week (and most do not reach that). Individuals with a more mild form of HPE may have only slight retardation and relatively normal facial appearance.
The causes of HPE in humans and animals are highly variable. Environmental influences, such as alcohol and drug use during pregnancy, have been implicated. Maternal diabetes has also been shown to have an effect. Chromosomal abnormalities (such as having 3 of a certain chromosome instead of the usual two) and several genes and signalling proteins (such as sonic hedgehog) are also known to cause the disorder when defective.
Photo credit: Pisces Fleet Sportfishing.
Leroi, A. M. (2003). Mutants: On the form, varieties and errors of the human body. Hammersmith: Harper Collins