We often say that competition starts soon after birth, but actually it starts from the womb of the mother or in an egg more exactly it starts from the embryo stage of the organism.
In sand sharks there are two uteri. In both the uteri numerous eggs are released simultaneously. Many eggs are fertilized. Fertilized eggs soon develop into the embryos. Freshly developed embryos start eating up the unfirtilized eggs. This phenomenon is called as oophagy. Healthy embryo also eats up the weak embryos which is called as embryophagy. Both oophagy and embryophagy are the examples of intrauterine cannibalism.
Finally only one embryo gets a chance to be born from each uterus.
For the Zoology students it is necessary to point here that according to J.P.Muller and Henle, sand shark comes in the systematic position as follows :
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Selachimorpha
Order: Lamniformes
Family: Odontaspididae
Genus: Carcharias
species: tarsus
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