C’est quoi le décompte chromosomique?

Les cellules humaines ont un nombre de 46

This illustrates a result of natural selection pressure on them and the connection between form and function.

Explanation:

It is due to natural selection and adaption of species which allow the broad and ridged teeth for grain-eating animals like in horses and pointed teeth for flesh-eating animals.  

This natural selection and adaptation of species allow them to fit in their environment and survive. Natural selection favored the favorable traits which became more common over time in these organisms and allow their teeth to gain specific structure which perform a specific function. So their teeth form is structured according to the function they perform.