Because Theyr lungs don’t get enough air they are supposed to
protons, neutrons and electrons
Endometriosis
This occurs when the tissue that lines the womb called endometrium proliferates to other regions outside the uterus. The displaced endometrium is still subject to reproductive hormonal changes such as thickening and breakdown as it occurs in the womb. This causes complications with painful symptoms.
Their bodies taper to points at both the snout and the tail, reducing water resistance. Also decreasing drag -- and therefore noise -- are dermal denticles, sharp scales that cover the skin of most shark species. Rather than bone, sharks have cartilage, which is much lighter and more flexible. In addition, their livers produce squalene, a fatty oil that helps them remain afloat. Their pectoral fins allow them to quickly change direction, dive and swim upward.
http://animals.mom.me/unique-adaptations-sharks-survive-7845.html
