Variation: Individuals within a population express different traits. Overproduction: An environment is incapable of supporting an overly large population. Survival of the Fittest: Organisms that are most suited to their environment don't get eaten and then they can reproduce. Inheritance: Offspring recieve traits from their parents that help them survive.
Definitions of The Principles of Natural Selection
Survival of the Fittest
In this population there are geese who are very aggressive and violent while there are also very gentle and mild tempered geese.
The geese's original habitat at the pond is not big enough for all the geese so disease is spreading more quickly and killing more geese. Most have migrated to the city to escape the outbreak.
Different traits in an organism can make it better suited for the environment. The gentle geese are not likely to survive because they are very easily over powered by the pesky human predators.
The aggressive geese fit this new environment because they are able to protect themselves from civilians who wish to drive them out of the park. This aggressive trait has enabled them to survive and reproduce new geese which will inherit it.