Fitness and Selection

 

Absolute fitness is the number of offspring an organism will have while relative fitness is the reproductive rate. Let's say that in one forest we have two types of similar fury organisms with different eye colors. One has pink eye and the other has purple. The pink eye organism has an average of 6 offspring and gives birth to one at a time while the purple eye can give birth to 2 offspring at a time. 

Positive selection: the color of the environment is pink and the prey prefers purple eyes. 

over time the pink color eye organism population will continue to increase because they are making it to adulthood which leads to reproduction. The purple eyes organism will slowly disappear.