Apparent Uptick in Cetacean Conjoined Twins

An article by John Albinson on CBS News, June 15, 2017,  “Fishermen catch extremely rare 2-headed porpoise in North Sea” mentioned a statistic that made me do a double-take: copy

Reported in The Netherlands in articles like, June 7’s “Siamese bruinvistweeling opgevist uit de Noordzee“, mentioned the discovery was from a week before that report.

Nine other, so 10 total, of cases of conjoined twinning in whales, porpoises and dolphins, worldwide in the known history of this world.  Just ten in however many centuries, as of mid-June 2017.    I find that striking, because…

Around June 1, 2017: Conjoinded twin Porpoises, off Dutch Coast, North Sea (see above).  Many of us will recall the January 5, 2014: Conjoined twin Grey Whales, Baja California, Mexico, Pacific Ocean (“could be first case for this species” – See National Geographic, Jan. 10, 2014), as well as the August 14, 2014  National Geographic report, “A dead two-headed dolphin that washed ashore in Turkey earlier this week ” (“only the third that is known to have lived beyond the fetal stage,”

The last article also mentioned: “the fetal abnormality is extremely rare in wild mammals:   Between 1671 and 2006 there were only 19 recorded cases.”  335 years of observations…   (That’s an average of one case every 17 and a half years, or roughly just over a case for two decades, including both land and sea mammals.  From the two statistics combined, it can be deduced that of the 19 cases of ‘mammals’, a maximum of 7 were cetaceans.  In other words: the average frequency of a conjoined twins in all species of dolphins, whales and porpoises is less than one such a discovery every 47 years.  Just over two per century basically.

Though I know that technically you can’t take such short periods to compare averages, it is still striking to suddenly go from 2 per century to “an average of 1 per year” (2 in 2014, 1 in 2017), and all in the Northern Hemisphere too.  That leaves me to wonder if ‘something’ happened that makes such unusual genetic mutations occur just slightly more frequently?  [sarc.]


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