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Evolution refers to the change in the inherited traits of a given population of living organisms through successive generations. It is also known as biological, genetic, or organic evolution (Levins 1965). As time passes, we find that variants with particular heritable traits in a way become more or less common. It is important to note that a trait is a given character, which is because of the interaction between genes and the environment. Traits can be anatomical, biochemical or behavioral. Variations can be caused by several factors (Odenbaugh 2001b). For instance one source of heritable variation is mutation, which leads to the introduction of changes in genes that can be passed on to the offspring as a result of reproduction hence bringing the possibility of giving rise to organisms with alternative traits (Puccia and Levins 1986). Genetic recombination is another source of variations. It leads to shuffling of genes into new combinations, which result in organisms exhibiting different traits. A third reason for variations is whereby genes are transferred between species. For example, the transfer of antibiotic resistance between different species of bacteria is well documented. Wholesale incorporation of genomes although extremely rare, is possible because of endosymbiosis (Mikkelson 2000).
There are two main processes which cause variants to become either more common or even rarer within a given population group. One of these processes is the natural selection through which we find that the traits for reproduction become more and more common while the ones that hinder it become more and more rare. Natural selection is because for any given generation, available resources limit the number of individuals who reproduce because they can only support a limited number (Levins and Vandermeer 1990).
The other process is the genetic drift; it leads to random changes of in how common traits are in a population group. It is most notable in situations whereby traits do not influence significantly influence survival- this especially among the small populations, whereby chance plays a very disproportionate role in the frequency in which genes are passed to the off springs (Grove et al 1993).
Ecology refers to knowledge or studying the earth and hence knowing why a balance should be sought because organisms are supposed to be compatible together (Richard 1980). Earth is a living entity that is constantly changing, the various life forms inhabiting it like plants animals and human life are also frequently changing, and hence equilibrium must be found in order to maintain life. In short, we can call ecology that study of the inhabitants of planet earth and how they interact with each other as well as their natural resources (Lloyd 1987).
Mass extinction is the vanishing from the earthâ€™s surface of a large number of the earthâ€™s species in order to open up other ecological niches for the other species to fill up. In the earthâ€™s history, there have been more than ten such happenings. One of the best-known mass extinctions happened at the end of the Cretaceous period. During this time, the dinosaurs and many other plants and animals disappeared and with them up to 76 percent of all the marine genera. It is generally believed that extinctions resulted from drastic changes in the environment because of events such as meteorite and comet impacts or massive volcanic eruptions during those periods. Apart from eradicating a very high percentage of both land and see creatures, mass extinctions also opened new ecological niches hence allowing surviving species to thrive in new environment and helping in diversity (Lodge 2002). The extinctions however, never conformed to the usual evolutionary rules, which regards who survives because it seems that the only factor that improved a family of organismsâ€™ chance of survival was widespread geographic colonization when the event occurred (Castle 2000).
There are many random past events, which had a profound effect on the result of evolution, one of them and which I have just explained is the mass extinction. However, there are others like ice ages and continental drift. Because mass extinctions are responsible for a thorough change in the dominant life forms, they are very useful in explaining the diversification of life in the past. Most of the major changes observed over the past 250 years would not have taken place if mass extinct had not occurred on planet earth. Although these events were largely random, just like mutation and drift they introduce a chance in the process of diversification. The ultimate breakthrough of modern animal life was associated with the Cambrian explosion, which started around 541 years ago. The rapid development of the complex and skeletonized animals and the general increase of the evolutionary tempo were related to the appearance of the burrowers as well as predators (Loehle 1990).
Due to this, many animals embarked on an evolutionary journey and came up with some body parts like the calcareous shells to protect themselves .Once developed, these hard parts allowed life to operate more actively with swimming, running and hunting. Many life forms have evolved since that mass extinction. For example before then, vertebrates lacked bony skeletons, but by the Ordovician period armored fishes had began to appear (Castle 2000). It is important to realize that during several periods, mass extinctions have crushed the diversity of life. After the appearance of armored fish invasion of land followed. The plants were the first followed by scorpions and later the millipedes. Later, amphibians moved to the land and it is from them that all the modern tetra pods evolved as well as the birds, reptiles and the mammals. The later originated in the late Triassic which was around (210 million years ago). During this period we had rat and mouse sized nocturnal animals that had highly sensitive ears, eyes and noses as well as improved intelligence in order to avoid the predatory dinosaurs. During the mass extinctions, which happened at the end of the Permian period, almost 90 percent of plants life became extinct as well as 70 percent of animals (Buege 1996).
A symbiotic relationship refers to close and mostly long-term interactions between different biological species. It has also been described as the living together of unlike organisms. This relationship is parasitic, commensal, or mutualistic. Many scientists have argued that the most immense species that are likely to be rendered extinct any time are the insects. For example, a recent increase in numbers of crop eating insects as been shown to be related to the decrease in the number of insect eating birds and not that their environment has improved (Cuddington 2001. One of the most disturbing and terrific examples is the leaf cutter or parasol ants that are seen in the neo tropical forests. These ants usually ascend the trees, which are only indigenous to the rainforest ecosystem and cut out small pieces of leaves and flowers. This is the only source of food for these insects. As large swathes of the rainforests are eliminated, soon these ants will be eliminated as well (Looijen 1998). We should note that all lives within a rain forest are interdependent and with the elimination of one comes the extinction of the other; this is because even the seemingly very small changes in the changes in the habitat or a species can have a terrible effect on the ecosystem (Odenbaugh 2001a).
Statistical evidence of marine losses at the end off the Permian suggests that the decrease in diversity was caused an increase in extinctions instead of decrease in speciation because during this extinction, the organisms affected were generally those with calcium carbonate skeletons and mostly those, which relied on CO2 levels to produce their skeletons (Justus 2002). Among the benthic organisms, background extinction rates were multiplied by the extinction event hence causing most damage to taxa that had a high background extinction rate and by implication the taxa with a high turnover. Extinction event among the marine live was a catastrophe with the ammonoids, which had been in a long-term decline for around 40 million years since the middle Permian suffering a selective end- Guadalupian extinction pulse. This greatly led to reduced disparity and it may have been has a result of environmental factors.
Therefore, mass extinctions are main precursors of evolution. These extinctions are preceded by serious ecological upheavals and hence changes in the ecology where the organisms have to live. For example, the organisms, which survive during this period, have to come up with mechanisms coping with the changed environment. In addition, when some species become extinct, their prey might become so many that the ecology cannot support them (Snel 1999). This is bound to lead to environment degradation. In addition, when the prey become extinct and their predators are still alive, the predators may opt for alternative forms of prey. For example, it has been widely documented in African national parks and game reserves that when the herbivorous are scarce to come by, carnivores like lions and cheetahs turn to attacking people (Orzack et al, 1993).