In suggesting the process of natural selection as the means resulting in evolution, Charles Darwin shows how evolutionary changes have occurred in organisms. Genetic change through time Understanding natural selection is paramount to our comprehension of evolution. is a much more accepted than the theory man has evolved from apes. Despite the fact that we are unable to prove without a shadow of doubt that man has evolved from apes, natural selection is relevant to the changes that have occurred over the years in humans.
Charles Darwin s theory of natural selection was based on two observations, first the fact that all species exhibit variability, for example height, colour, etc. Secondly all organisms than survive to reproduce. To understand why natural selection is much more acceptable than the idea of evolution from apes, we must first understand the Principles of Natural selection. The first principle of natural selection is that a species must be capable of reproduction of more than enough offspring to replace itself. Secondly, the environment may affect ones chances of survival. Third, because each individual is unique some may have more chances of survival than another. Lastly, the ability to adapt to ones environment increases ones chance for survival. After the acceptance of these principles, one can understand how change through time or evolution must have occurred in the past and continues to occur today.
The reproductive capacity of most organisms is enormous compared to the number of offspring that reach maturity in each generation. For example spiders can produce hundreds of offspring, dogs and cats produce fourteen or more offspring in a litter and human beings may produce ten or more offspring in a lifetime. It is this reproductive capability that fulfills the first of Darwin s principles. By reproducing we are continuing the life cycle allowing for more of each creature to exist in the future. It is the objective of each organism to try to ensure the future existence of its species through reproduction. It is this objective that explains attraction to the opposite sex and why certain traits are selected for in a mate. Although it seems the selection of a mate is random, it actually has more to do with ensuring the survival of ones gene pool than we realize. Humans select unconsciously according to what we believe to be the traits that will be selected for by nature. However, if all the offspring were to survive, the biosphere would be so crowded that eventually there would be no room for new organisms. So following the first of Darwin s principles, organisms are capable of reproduction, however the second principle keeps overcrowding from happening.
Killing thousands of people and animals each year, disasters such as flooding, tornados, earthquakes, drought, disease and infestation carry out the second of Darwin’s principles. Although it is saddening to realize that many must die in order for others to survive, this is what is referred to as survival of the fittest. It is these unforeseen disasters that are responsible for genetic drift, a process in which the genetic makeup of the population changes by chance over time instead of being shaped in a nonrandom way. The environment decides which organisms will live and die through natural disasters and those who can adapt to the changes that have occurred in the environment. Due to adaptation, organisms are able to keep from getting completely wiped out however; this does not guarantee the further existence of a species. It is important to notice that selection produces adaptations that benefit individuals. Such adaptation may or may not benefit the population or species. The species or population as a whole may not benefit because change has eliminated that breed and created a new breed that is more adapted to the requirements of the environment, for example temperature changes requiring fur verses no fur. The environment affecting ones chances of survival is not only due to natural disasters, if the environment changes the organisms in it must be capable of change as well. With out change or adaptation of the organism in a changing environment, continued existence is not possible. That is to say, a deme cannot afford to vary greatly in a stable, competitive, and hostile environment, for random variation may be lethal; the deme must remain well adapted. At the same time, the deme must be able to change, evolve, in adaptation to environmental change. This necessary genetic stability, accompanied by flexibility in the form of adaptability, is the basis of Darwinian fitness, and the balance struck between these two factors determines how fit a population is. Change for organisms is a delicate balance since survival depends on the right changes for the environment. Lack of adaptation is just as deadly to organisms as natural disasters, if not more so.
Each organism is an individual and differs from other organisms in many ways. Being diverse keeps the world interesting, but more than that it makes chances for survival unpredictable as well. It is organism s differences that can increase or decrease the probability of survival. If organisms in a niche were all white and a factory was built near the niche depositing black ashes throughout the area, the white organisms would be visible to prey and would be eaten. The only chance of survival would be to have the white organisms produce darker offspring that were adapted to the new environment. It is not enough to reproduce organisms must evolve through reproduction. It is this concept that makes reproduction so competitive. This proves Darwin s third principle that unique individuals may have a better chance of survival. It is the differences of the darker offspring that would give them a better chance of survival.
The increased chance of survival, due to the ability to adapt to the environment is the last of Darwin s principles. It is not by accident that organisms are matched with their environment; it is because of their ability to adapt or evolve to the surroundings. For example if one type of tree grew very tall in a forest, it may out survive other smaller trees since it would now have access to the sun and shade smaller trees from that most precious and needed commodity. Organisms are suited to their environment not the other way around. Genes compete with one another for survival, and the organisms with the successful genes will pass them down to future generations. Or to put the matter in the backward form: the genes that exist in animals or plants today are the successful ones that have been passed down through previous generations and have not become extinct. Natural selection makes sense both from a present point of view as well as a past perspective. The diversity of life results from the splitting of one species into two or more. Over time, natural selection may cause each population to become better adapted to its environment, leading to even more changes for each species. Through the use of fossils we are able to see the evolutionary changes that many organisms have gone through. Anthropologists have shown examples of previous humans that show that we have had to undergo changes in our structure in order to adapt to a changing environment. For example our jaws are not as strong as they once were, because we no longer each uncooked meat. Continental drift explains some geographic trends in evolution as well. As each of the continents has moved over time, species have been separated and have had to adapt to their own individual area. It is therefore possible to have one species be the original for two completely different areas. After a characteristic has been selected for in an area, it is produced in the offspring thereby ensuring that they are suited for survival. For example, if an area has vegetation but very little meat, early man may have lost his strong jaw sooner. Meanwhile in another area where there may be an over abundance of animals for food, early man would need to maintain the heavy jaw for strength in chewing raw meat. It is extremely important for individual survival as well as survival of the species, that offspring are adapt to the needs of their individual area. However, if the environment undergoes any changes, so too must the organisms. After understanding the four principles of natural selection, imagining humans evolved from apes does not seem far-fetched at all.
What seems so simple was in fact extremely controversial for Darwin s time and still is today in many parts of the western world. Natural selection suggests that life on earth is a result of billions of years of adapting to a changing environment. Fossils of
Previous ancestors dating back thousands of years seem to further prove the idea of natural selection. We are able to look at natural selection from back to front as well. If we look at remains from past humans we are able to see the changes that we have undergone over time. Although we are unable to prove in fact that humans have evolved from apes, it is evident natural selection is extremely significant to the changes that have occurred in humans over time.