Now scientists have concluded that this is not just a response to crowded conditions but represents an evolutionary strategy that allows the most aggressive male sharks to father the successful baby and thereby outcompete sexual rivals.

“For most species, we think of sexual selection as ending when males fertilize eggs, because once the male’s fertilized eggs he’s won, there will be some genetic representation in the next generation,” said Stony Brook University marine biology professor Demian Chapman, lead author of the study published online Wednesday in Biology Letters. “This is demonstrating that embryonic cannibalism is actually whittling down the number of males producing offspring.”

It’s still unclear whether the evolutionary strategy works because the most-aggressive fathers get their offspring growing in utero before others, thus giving them a developmental advantage in the cannibalistic battles to come, or if they produce offspring that gestate more quickly.