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Reports of terrifying two-headed sharks have become increasingly common in recent years, and scientists say it is all the fault of humans.
Most recently, one of the abnormal beasts stunned fisherman in western India in 2020.
The first two-headed shark is believed to have been spotted off the coast of Australia in 2008.
READ MORE: Schoolboy, 12, catches monster 11ft great white shark weighing 500lb on trip with mum
There have been multiple reports from both the Gulf of Mexico and Gulf of California, where fishermen previously said they were finding more and more.
And in 2016, scientists at the University of Malaga discovered a two-headed shark embryo that had "two hearts, two oesophaguses, two stomachs, two livers".
None of the sharks have been fully grown and it remains unclear whether it is possible for them to live into adulthood.
Patrick Rice, chief science and research officer and principal investigator for marine research at the College of Florida Keys, has analysed the bizarre creatures.
Explaining how a two-headed bull shark found off the coast of Florida came to be, he told Newsweek it was a conjoined twin. Its skeleton and internal organs divided halfway up its body, creating two perfectly formed heads.
He said: "The phenomenon occurs as a result of the incomplete division of a single fertilised egg, exactly like conjoined humans."
The sharks can also form from random genetic mutations, as is thought to be the case with the two-headed embryo found in 2016.
Nicolás Ehemann, a researcher from the Ichthyological Collection of the Interdisciplinary Center for Marine Sciences, reckons the phenomenon is being caused by humans.
Specifically, overfishing is thought to be reducing the gene pool, which has a knock-on effect regarding the quality of offspring.
He told Newsweek: "The constant increase in fishing efforts on sharks from the 1980s to the present has undoubtedly depleted the populations of different species.
"This has had repercussions, among other things, on the genetic diversity of the species, smaller sizes at maturity, and sexual reproduction that can affect the quality of the development of the embryos.
"All these external stressors may enhance DNA mutation and incomplete splitting of the axis during embryonic development, resulting in abnormal individuals."
However, both Ehemann and Rice said the increase in reports might not be down to overfishing making the sharks more inbred.
Instead, it could be the prevalence of smartphones meaning more two-headed sharks are photographed, hence the increasing number of reports.
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