Scientists think they may have finally figured out why shark embryos cannibalize their siblings in the womb. The shark pregnancy process used to be a great metaphor for just how scary those animals are, but now we actually have a bit of insight into why they do what they do.
According to a study published in the journal Biology Letters, it's part of a struggle wherein babies from different fathers compete. The researchers studied shark embryos from sand tiger sharks at various points of the pregnancy and found that the later in the process it was, the more likely the remaining shark babies were all from one father.
This led them to believe that the cannibalization is part of a competition through which males establish their paternity.
"In some species, the struggle for paternity continues beyond the point where the female [mates with] the male," said Demian Chapman, study co-author and marine biologist at Stony Brook University of New York.
To help confirm their hypothesis, the research team used DNA testing to determine the paternity status of each baby. The researchers found that litters with five to seven embryos had at least two fathers.
"It's exactly the same sort of DNA testing that you might see on Maury Povich to figure out how many dads there are," Chapman stated.
What scientists don't know yet is why one father's offspring grow bigger faster.
The sand tiger pregnancy process is pretty grisly. Through the process, all but one of a litter of 12 fetuses are eaten by the largest baby. This competition begins about five months into the yearlong gestation period. It allows the species to have much larger babies than other shark species.
"Sexual selection is very much like an evolutionary arms race, and the males and females are basically one-upping each other," said marine biologist James J. Gelsleichter
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