Heredity and Natural Selection

Introduction

The major proponents of the theory of natural selection are Charles Darwin and Alfred Russel Wallace, who were scholars coming from different regions. Wallace (8 January 1823 – 7 November 1913) is said to have been a British scholar known for solely suggesting the evolutionary theory as a result of natural selection.

This move motivated Darwin to make his theory known to the public. At the collegiate School located in Leicester Wallace employed to impart knowledge on mapmaking drawing and surveying. Here, could access the library and spend enough time reading.

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At some point he came across Thomas Malthus essay on the principle of population. Also it is here that he met Henry Bates an entomologist who introduced him to the liking of collecting insects and this interested him much. This went on even when they moved to Brazil. Only this time some of their specimen was sold while the rest was left for investigation purposes.

On the other hand, Charles Darwin (1809-1882) a British has made quite some remarkable contribution on the subject. However we can not say he conceived the idea, it was there before he was born. Darwin was sent to Cambridge University after dropping out of his medical studies in Edinburgh, Scotland.

Here he enrolled himself to theology and his life took a turn towards his career. He met and developed interest in the ideas of Adam Sedgwick and John Henslow who were geologist and naturalist respectively. He dedicated time to work with them and even began adopting some of their concepts like lack of faith with the theory of biological evolution.

These and other events triggered the scholars towards formulation of the model of how and why evolution occurs. Evolution is said to occur through the process of natural selection.

This process of natural selection is a process through which organisms possessing certain traits in their gene structure have advantage over other organisms located in the same habitat in their chances of survival as a result of stiff competition for scarce resources.

Only those organisms that are best adapted for a particular habitat survive when the prevalent conditions are not favorable. Natural selection takes effect when species possessing different traits regroup into smaller pools of those with similar traits and they separately reproduce causing further drift.

Different pools will exhibit differences in reproduction patterns depending on certain factors, e.g. those that are preyed on much are likely to be fewer in numbers as they reproduce at a slower rate. The pools with larger populations are bound to increase more since they reproduce and give rise to species with similar genetic traits.

The end result is that the populations that possess gene traits that are advantageous continue to dominate in numbers and eventually as the process selectively favors the population with better traits the other population becomes extinct (Ridley, 2003).

However, this theory of evolution by Darwin and Wallace have been borrowed and revised by other scholars to explain some of the basic concepts in modern population genetics. For instance, we can talk of Hardy Weinberg and his equilibrium, microevolution and genetic drift concepts.

His argument states that the allele frequencies and genotype frequencies remain unchanged or are at equilibrium and are passed through generation to generation, which in essence implies that evolution doesn’t occur, unless triggered by certain conditions.

In small populations for instance the there is random distortion of the allelic frequencies which distorts the equilibrium while large populations do not easily permit exchange of gametes which in turn implies that the equilibrium is maintained even in the course of where natural selection is prevalent.

For the equilibrium to maintained, the population must be in isolation from the rest of the gene pools which means there is no gene flow. Mutation should not occur for natural selection not to happen. For the population to remain in isolation for generations there has to be random mating which means the pool doesn’t mate with those that are of distant parenthood. This way the equilibrium is maintained.

It requires that natural selection does not prevail which means population wont have differences in traits. Hardy Weinberg’s equilibrium is however difficult to achieve considering the populations are in their natural habitat where these conditions are not controlled. Weinberg understood that for evolution to take place then there has to be occurrences prevalent on a population’s activities to trigger evolution.

For this reason he came up with an equation with which he could determine the probability of genotype frequencies in any population and make a follow up of any changes from generation to generation. This equation has earned the name Hardy-Weinberg equilibrium equation. It can be defined as a state within which evolution does not take place. This happens in the rare occurrence that some five conditions are met.

The equilibrium equation has aided geneticist obtain the likelihood of a certain trait occurring in the genes of an offspring with reference to the genes of the parents in their endeavor to survive with the prevalent conditions. This in one way or the other relates to Darwin-Wallace’s model of evolution. It suggests that there are five necessary conditions meant to prevent evolution.

However, in the real world for those condition not to occur would be a rare or impossible situation, hence evolution still prevails. The two schools agree on natural selection and mutation of offspring. Besides this they come into agreement when they suggest that evolution is a gradual process across the generations of an organism and never is it at a constant rate.

As a result of large population sizes, natural selection occurs separately which means there is high prevalence of speciation with separate species possessing different qualities as those that are distant. Both schools of thought however agree that for these changes to take effect which means evolution occurs, it takes long periods due to the rare nature of environmental changes.

The result is that the species remain in the same state for long extended phases and even when the rare change occurs, it is occurs in selected pools due to speciation brought about by large population sizes. This in other word is the punctuated equilibrium. These findings also apply to speciation (Ridley, 2003).

In conclusion, Darwin and Wallace’s evolutionary theory play a major role when it comes to modern evolutionary theory. Natural selection is the basis through which nature chooses species that will be faced off the face of the planet and those that will remain and grow strong.

Some organisms adapt to the conditions of their environment. For example, some birds change the strength and shape of their beaks to survive other animals like the camel develops draught resistance traits.

Reference list

Ridley, M. (2003). Evolution. Chichester: Wiley-Blackwell Publisher.

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