NATURAL SELECTION: Those who survive the competitions will then go on to breed and these tend to have the characteristics that are better suited to the environment than those who don’t. Thus, there is natural selection or ‘survival of the fittest’.
ADAPTATION: Successive generations will tend to be more and more adaptive to their environment and will have characteristics that heighten their abilities to survive, to get food and most importantly to reproduce and all of this is a result of the process of Natural Selection. (Eg. If only fast moving prey survive then that species should evolve over the generations in the direction of becoming on average faster moving.)
Darwin believed that the increasing competition for finite resources exerts selective pressure because those who lose, when the resources are limited will fail to reproduce. People would believe that with the process of natural selection and adaptation that this would make the members of a species almost perfectly suited to their environment but Darwin didn’t actually believe this he thought: “Natural selection tends only to make each organic being as perfect as, or slightly more perfect than, the other inhabitants of the same country with which it comes into competition…natural selection will not produce absolute perfection.”
Darwin presumed that evolutionary change would on the whole happen relatively slowly over periods of hundreds or thousands of years. However there are reasons to why some aspects of behaviour seem to change more than others during evolution (Grier +Burke). Any behaviour that allows the most effective way to use the available resources around them (eg. Bigger jaws for eating whole animals)giving the individual a quick advantage increasing reproductive success. A behaviour which will give an individual a competitive edge will likely lead them to a rapid evolution (eg. A strong male who wins all his competitions will have the right to impregnate the female allowing his genes to be perpetuated). A behaviour that is used with respect to other members of the same species (eg. Courtship or communication) is likely to show evolutionary change as this will impress prospective mates due to the large benefits the successful behaviour brings. Lastly the forms of behaviour between two members of different species such as the predator and prey interactions may also be the subject to rapid change by both the species. (Eg. If the predator needs to run faster to catch their prey this selects for speed of movement in both the predator and prey, as the predator becomes faster meaning the prey must evolve faster speeds to escape, as those who survive must evolve into faster speeds.)
All characteristics possessed by an individual animal should serve the function of making them well adapted to their environment according to Darwin, however there are some characteristics possessed by species that don’t seem to serve any useful purpose, such as the long train that peacocks have, this could make them more vulnerable because it could decrease their immobility. Darwin thought that these trains must have some purpose, so he thought of sexual selection as a variation of natural selection: the peahens find the peacock’s long train attractive, so those with the long trains have more reproductive success than those with short ones, turning this characteristic into an advantage and an adaptive trait.
The peppered moth is a good example regarding Darwin’s theory of natural selection this was done by Kettlewell who studied two variants of peppered moth, one which was light and the other one was dark the difference of colour inherited. The moths are eaten by birds who rely on their sight to find them, he observed them on light and dark coloured lichen trees (trees were in polluted area) and found that the light coloured moths survived best on the light lichen trees and the dark ones on the dark lichen trees. According to Darwin’s theory, the number of darker moths should increase if the proportion of dark tress also increase.
