Darwin's Theory Of Evolution

Introduction

Evolution is a slow and gradual process that occurs over a long period of time. It is a very controversial topic that relies on a number of assumptions though it is considered by most to be the best explanation of life on earth. Many people believe that God created the earth, often referred to as ‘intelligent design’. Darwin was the keystone for the theory of evolution. He was one of the first people to study it in depth, and the first person to publish accurate scientific research with a plausible scientific theory about evolution. Darwin’s theory of evolution can be summarised into five observations and three inferences. Observations; organisms have great potential fertility, the size of a population is steady, resources are

The amount of darwins is calculated with the trait values at the start and end of the study time period, x1 and x2, with Δt representing the overall time period in millions of years. This is all calculated in this following equation: (lnx2 – lnx1)Δt. Calculating this allows evolutionary biologists to better understand the history of a species by calculating the speed at which certain traits may have evolved and what selection pressures the species was facing at that particular time (Svensson). Brisk and sudden bursts in the rate of selection are able to cause significant modifications in the evolution of a species (Svensson). This shows that the rate of evolution varies, and is influenced by various factors. (Damgaard) stated that the fossil record shows that the rate of evolution varies, and investigated the link between population size and evolutionary rates. This relates to the carrying capacity of the population and Haldane’s review of natural selection in terms of reproductive success (Damgaard). Haldane found that in an unbounded haploid population, for an allele that is advantageous to become fixed, there was a certain cost of natural selection in the population. This means that an excess in reproduction is needed in order to select for an advantageous gene, and this is considered to be a limiting factor in the rate of evolutionary process

Two of the most important factors when considering rapid evolution are the generation time and environmental conditions throughout the life history of a species. For a species to evolve rapidly, it must have certain selection pressures, such as the aforementioned mass extinction which can lead to rapid evolution, or short generation times which would result in higher mutation, and therefore higher adaptation rates. Adaptation relies on random genetic mutations, and as a more favourable mutation survives, it is more likely to be passed on to the next generation. Long-lived species are therefore more restricted, being unable to change or adapt at the same rate as the faster evolving short-lived species (WEB jrank). An example of a fast evolving species is that of the Southeast Asian tree shrew (Tupaia belangeri). A study by Jiannan Lin investigated the genetics of the shrew in order to establish its position on the phylogenetic tree. They found that some genes were more closely related to Primates while others were more closely related to Glires. This is because the genes evolve at different rates. This is important because it shows that there are different selection pressures at various stages, and that not all genes evolve at the same rate