Four Forces of Evolution


Evolution is the series of changes through which organisms transform from their simplest and original states to more complex states. The changes take place over many generations continuously and occur in genetic properties or traits that are passed down the generations. This translates to the present state being only a phase in this unceasing process of change. Evolutionary changes happen only when certain come into play.

  • The first force is natural selection whereby the best-adapted individuals produce most offspring, hence carrying forward the genes that made them better off. This in turn makes the better genetic traits more dominant while the undesirable traits become less dominant in a population. Ridley says that, although natural selection affects the phenotype (physical traits), the genotype determines the traits. With time, the undesirable traits disappear entirely and cease being passed on to the following generations and the desired traits become dominant.

  • The second force is genetic drift, also referred to as allelic drift. This is the random change of gene frequency as a result of random events in smaller populations. This brings about random changes of the distribution of phenotypes that contribute to the next generation. According to Smith the chance of having random deviations from the average is inversely proportional to the size of the population.

  • The third force is gene flow, also called gene migration. It occurs when genes are transferred from one population to another resulting in genetic composition change of the new population. Population in this case refers to a group of individuals within which reproduction takes place. O’Neil notes that gene flow happen when organisms move from one population to another and mating happens.

  • The fourth and final force is mutation is the sudden and permanent random change of an organism’s genetic composition resulting in new traits that are passed on to the next generation. Gene is found in DNA, the hereditary material of life. DNA is responsible for the shape, size, behavior, and in general the whole life of an organism. A change in DNA results in genetic properties’ changes which give rise to enormous changes in all aspects of an organism’s life. Mutation is a force of evolution mutated gene is transferred to the organism’s offspring, hence, the next generation. However, some mutations occur in nun-reproductive cells and therefore evolution does not occur.

In conclusion, the four forces are responsible for both micro and macro evolution which brings about new species and change in allele frequencies respectively. They have brought about evolution of all organisms over many generations and will go on for many years to come.

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