Organism who are "fittest" survive because they are best adjusted/adapted to their environment. (Explained by Charles Darwin)
<em>So</em><em>,</em><em> </em>while the traits of the adapted parents <em>do</em><em> </em>get passed down throughout generations, "fitness" does not necessarily refer to breeding and passing traits specifically, but rather, who lives and who dies (Natural Selection.)
They are called ENZYMES. Enzymes speed up the rate at which the digestion process occur so that the nutrients in the food can be absorbed by the body and used for the development of the body.
