Natural Selection & Evolution Essay
The theory of Evolution by Natural Selection explains the diversity of Living Things and is supported by a range of scientific evidence – discuss

The theory of evolution by natural selection is the process where an environmental factor acts on a population and results in some organisms having more offspring than others. This theory was proposed by Charles Darwin, an English biologist in 1858. He meant by this that the selection was done by nature, not humans and therefor the reason it is called natural selection. Scientific Evidence supporting this theory is abundant and includes variation, specification, artificial selection, homologous and analogous structures and much more.

Variation (micro-evolution) is part of Darwin’s theory of Natural Selection. Darwin concluded that Natural selection could only occur if there was variation in the population. Since then scientist have determined that Variation is caused by different genes, which result in different characteristics. They have also concluded that variation is an inherited thing. Since genes are inherited, so are the characteristics they carry. We can see variation in humans very easily. In humans we can see they have different noses, eye colour, hair colour, height, limb length, hairiness and skin colour. Most Variations are very easy to determine in organisms.
Speciation (macro-evolution) is the process by which one species splits into two or more separate species. High Biodiversity is the result of speciation. Speciation occurs in 3 basic steps: Variation, Isolation and Selection. For speciation to occur there must be variation in the population. Isolation is required for the formation of new species. This means different groups of the population are prevented by some mechanism from inbreeding. Isolation into separate populations occurs in several different ways like a geographical or climatic barrier. Once isolation has created the barrier, Natural Selection affects the Genotype and causes changes preventing the groups breeding even if they came back together in the future. Examples of possible changes are courtship behaviour for example animals develop different breeding songs, displays and rituals; Animals may breed at different times of the year; Animals may breed but the babies are sterile; and sperm may be killed by the chemistry of the female. Variation and Speciation are both apart of Natural Selection and are part of the evidence supporting it.

The Fossil Record is part of the Evidence supporting Natural Selection. We can see by looking at Fossils that earlier fossils were simple organisms and later ones were increasingly complicated which would make sense because new alleles and genes have developed. The Fossil Record shows that there is an increasing number of species that have lived on the earth. Many of these species have died out and become extinct along the way. The increasing number of species (biodiversity) supports the theory of evolution and speciation. We can see Homologous characteristics in species that are related, which have the same basic structure. Homologous characteristics are controlled by particular inherited Genes, as scientist have discovered. For example, a cats paw and a lions paw are considered homologous, but a cat’s paw and an insects foot are not homologous. They may have the same structure, but their functions are very different. Over the last few decades, scientists have isolated genes to study their chemical structure. From this they have determined that the more alike two organisms are the more genes they share. But Homologous structures don’t necessarily have the same function with the groups they share with. For example humans and whales both have 5 digits on the end of their limbs. For humans five finger on each hand and five toes on each foot. They are used for things like grip and walking. A Whale has five digits that form each of it’s flippers which they use to propel through