I was peacefully scrolling on Twitter one afternoon this week when I came across this tweet by Twitter user @ycsm1n, who posted a screenshot of a Reddit post about two-headed sharks captioned with “i’m sure that’s absolutely nothing to worry about”. Looking at the two-headed animal, I immediately had two thoughts: 1) Aww, it’s kind of cute 2) Um, what’s going on?
Rule #1 of the Internet is don’t believe everything you see online, especially if it’s on Twitter. I decided to take the time to investigate this tweet because now I want to know if two-headed sharks are actually a growing population, and if they are, should we be worried.
The picture in the tweet originates from a National Geographic article from 2016 entitled “Two Headed Sharks Keep Popping Up- And No One Knows Why”. One of the first records of a conjoined twin shark was actually a blue shark embryo that was discovered by a fisherman in the Indian Ocean in 2008. Then, a 2011 study found that blue sharks actually hold the record for the most two-headed shark embryos because that species of shark births on average 25-50 babies (Mass.gov).
Unfortunately, there is no one answer as to what is causing these anomalies. Various factors such as viral infections, genetic disorders, metabolic disorders, and even pollution could impact the number of heads a shark is born with. Additionally, overfishing could be to blame, as overfishing limits the gene pool, causing inbreeding which naturally causes genetic abnormalities.
The article concludes by stating that polycephalous (two-headed) sharks may not actually be more common, rather there are now more studies that have been conducted and published regarding this kind of genetic anomaly in sharks. There’s also not a large amount of information out there to begin with since seeing a two-headed shark is extremely rare.
Unfortunately, while a new and growing population of two-headed sharks would be very interesting for the world of marine biology, I think I’d prefer it if this species stayed closer to science fiction than fact. It would make a pretty good addition to the Jaws movie series, though.