A characteristic that improves an individual's ability to survive and reproduce in a specific environment is called an .

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

sex cells are usually half's then they find another half and make a fertilize egg