Scenario with component of natural selection
Case of sea turtles is overpopulation. Zebras case is variation. A lemur species case is adaptation. Overpopulation is an unwanted state where the amount of surviving human population surpasses the carrying ability of Earth.
Overpopulation is made by a fraction of constituents. Decreased death rate, high-grade pharmaceutical conveniences, and deficiency of valuable sources are few of the reasons which occur in overpopulation.
A small variation in the situation, quantity in specific frontiers. Adaptation is basically the method of changing.