when the ball is bounced gravitationally energy is released (more info below)
When a force is applied down to the ball, the gravitational potential energy is converted into kinetic energy before it hits the earth. Cinetic energy is converted into vibration, thermal, and static electrical energy, before the momentum of the ball pushes the ball back up into the hands of the people.
The four key components of natural selection are isolation, mutation, variation, and speciation. Or are you asking for key components of the theory of natural selection? if so, 1. Variation in population 2. Some variation is heritable 3. Reproduction + survival is non-random. 4. Individuals differ in their potential rate of surviving (and also reproducing).