Natural selection is a control that is found throughout all life forms and species. It is a true example of "survival of the fittest", where only the strongest, and most adequately adapted, survive the conditions. This may be due to an ever changing environment, stronger predators, or tougher competition for food. Once natural selection has occured, only the organisms best suited for survival are able to live, meaning that they will have a higher chance of reproduction - the ultimate goal for all creatures. Having reproduced, their offspring will inherit their strengths, causing them to have a higher chance of survival also.
Natural selection was seen largely through the evolution of Australia, during the period in which it broke away from Gondwanaland, and for some period after that. During this time, the climate of Australia was changing significally, and both plants and animals had to adapt to these new conditions in order to survive. The plants evolved quickly, producing flowers instead of reproducing using spores. This allowed them to conserve water as the country was drying out. Plants also developed leaves that were less spread out to the sun, as water was being lost to evaporation. This development of new plants caused many animals to evolve in order to adapt to this new source of food.

Natural selection can be clearly seen in many species of animals unique to Australia. In the case of the Quall, natural selection starts almost straight after birth. The female Quall gives birth to many offspring, but only has eight nipples in order to provide nourishment for the offspring. This means that only the strongest, most determined offspring will be able to receive milk, and therefor survive.
Natural selection is also evident in the life of a Kangaroo. In order to gain a mate, male Kangaroos will often have to fight other males. The outcome sees the strongest male reproducing and passing his strong genes onto the offspring.