This is an example of; evolution
Evolution is a gradual process in which the characteristics of a species are changed in response to its environment over several generations. Evolution depends on the process of natural selection. Some of the changed characteristics (traits) may be beneficial to the organism and it can be transferred to their offspring.
Well because they need to survive. And whoever gets the most food will grow the biggest and produce the most offspring. This even happens between inter species like ants, an example of this is when the red imported fire and caused the near extinction of the native argentine ant in the United States
When the swing is raised and released, it will move freely back and forth due to the force of gravity on it. The swing continues moving back and forth without any extra outside help until friction between the air and the swing and between the chains and the attachment points slows it down and eventually stops it.
