One of the more interesting (and disturbing) natural phenomenon is the intrauterine cannibalism exhibited by bull sharks. While multiple embryos are conceived, the strongest of them starts devouring its 'siblings' in the womb, usually sparing only one. This, rather extreme survival of the fittest, form of sibling rivalry has baffled scientists for ages. Sand tiger sharks and great white sharks have also been observed to exhibit intrauterine cannibalism.

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