Cannibal Babies

Known for being the predators of the ocean and with more than 465 different species, sharks have always presented interesting and violent behaviors about they way of living. One of them is the cannibalism before birth.

The sand tiger shark, is a very special shark specie. Even though, a female shark can carry around 5 embryos in their womb, only 2 get their way out to life.  When the baby sharks reach certain stage of development, they can not all fit in the mother's uterus. Therefore, a battle for territory starts and naturally, the smallest and weakest lost their space. For years, this behavior only had this proximate cause as an explanation. However, this was not enough for the scientists, who later discovered that this cannibalism was beyond of just not having space for growing up.

Shark females, mate with more than one male during the reproduction season. The mate involves a lot of violence, leaving the future mother with several injuries. Consequently, when the embryos are in the womb fighting to survive, the one with the strongest genes is in charge of make the natural selection effective and that the baby is worth the process.This, being the ultimate cause allows sand tiger sharks to assure that only the best will preserve the specie.
Basically, this cannibalism between siblings is a final battle of which genes deserve to be passed.