Natural selection is an important process in evolution where biological characteristics in a given population become either less or more common due to differential reproduction of the organisms. The presence of heritable genetic variation that leads to fitness difference is an important condition required for natural selection to result in speciation, adaptive evolution and novel traits. Genetic variation is as a result of mutations which may have effects which may be very advantageous or disadvantageous to the organism. Organisms with greater fitness levels have more probability of contributing offspring’s to the next generation while the ones with lesser fitness are more likely fail to reproduce or die prematurely. Due to this reason, alleles that averagely result in greater fitness are more abundant in generations that follow while the ones that had reduced fitness become rare (Pidwirny 2006).
Italian wall lizards are a perfect example of evolution by natural selection. Focusing in a research that involved introduction of these lizards to an island off the coast of Croatia, where they underwent rapid evolution that would take many years in normal situations. According to researchers, the lizards developed an absolutely new gut structure, harder bite and larger heads a few years after being introduced to the island (University Of Massachusetts, Amherst 2008). This habitat had its own population of lizards that were less aggressive compared to the ones introduced. This population was wiped out by the new species. The lizards introduced to the island adapted to their new habitat in ways that speeded up their evolution physically (Kimberly 2006). A significant observation of their evolution was new structures in their gut system and head. Their gut system physical characteristics were not developed to digest a vegetarian diet. However, researchers discovered that they developed cecal valves that slowed down digestion of food in fermenting chambers hence allowing them to process the cellulose in vegetation into volatile fatty acids. The ability to bite harder is another adaptation that led to its head evolving to be longer and wider which translated an increased bite force. The observed change in head morphology is owed to adaptation to a different food source. This physical evolution led to changes in the lizard’s social and behavioral structures (Kimberly 2006).