If, however, this car is entered into an endurance test alongside other cars that have effective fuel gauges, it becomes slightly disadvantaged. The probability of its completing the test is slightly reduced. The life process, in fact, is an endurance test upon living organisms, and evolution is what creates new models. Outcomes are expressed not in certainties, but in probabilities. The slightest edge may lead one strain after many generations to live and pass on its changed genes, while another fails and becomes extinct.
Genes are less obtrusive than diprotodons, but clearly they control it all.
It is common knowledge that in many species miniatures and giants exist. In wild populations, this happens with chimpanzees, horses and humans. There are, likewise, many domesticated breeds of dogs, horses, goats, pigs and chickens that display extremes of growth habit. The biggest mammals existing today are the whales, and even these animals have close relatives, such as dolphins, which grow to much smaller maximum sizes. It is known that growth is regulated by genes.