Variation, a term used in genetics, refers to a genetic event that causes the individuals or groups of a certain type or species to possess different characteristics from one another. Genetic variation is a result of subtle changes in our DNA. Mutations are a big source of genetic variation, but mechanisms such as sexual reproduction and genetic drift often contribute to it as well. Genetic Variation is a term used to describe the variation in the DNA sequence in each of our genomes. Variation always takes place within the limits of genetic information. In the science of genetics, this limit is called the "gene pool." All of the characteristics present in the gene pool of a species may come to light in various ways due to variation. For example, the beaks of the Galapagos finches differ according to their way of obtaining food. However, Darwin was not aware of this fact when he formulated his theory. He thought that there was no limit to variations. According to Darwin, animal breeders who mated different varieties of cattle in order to bring about new varieties that produced more milk, were ultimately going to transform them into a different species.
Inheritance of learning and adaptations depend on direct transmissions from parents to offspring, either through asexual reproduction or sexual reproduction. This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent cell or organism. Charles Darwin was a firm believer in the inheritance of acquired characteristics. In his book The Variation of Animals and Plants Under Domestication, Darwin gave many examples of the hereditary transmission of adaptations. Darwin knew nothing of genes or random mutations, which only became part of biology in the twentieth century. In order to understand, for example, how a dog could inherit something a parent had learned, or how a plant’s descendants could inherit its adaptations to a new environment. He put forward his own theory of heredity in the The Variation of Animals and Plants Under Domestication, entitled ‘The Provisional Hypothesis of Pangenesis.’
According to Darwin, fitness means the capacity to survive and reproduce. This property includes a variety of behavioral factors—elements which are highly contingent on the environmental conditions that the organism experiences. In situations where competition involves the location of resources, fitness can be described by foraging ability; when the ability to evade predators is at issue, fitness will involve visual awareness; in problems involving competition for mates, the capacity to intimidate rivals will become the dominant trait. These behavioral features are highly qualitative predictors of net reproductive success.
A selective pressure is any reason for organisms with certain phenotypes to have either a survival benefit or disadvantage. Selective pressures can take many forms, including environmental conditions, availability of food and energy sources, predators, diseases, and even direct human influence. Selective pressures drive natural selection. Some members of the population will not survive and reproduce and thus will not pass on their genes into the next generation. Gradually, the population changes, and genes that improve survival and reproduction will become more common, while genes that are disadvantageous to survival and reproduction will become more rare.
Darwinism Refuted.com. (n.d). Darwinismrefuted from http://www.darwinismrefuted.com/origin_of_species_01.html
Mcz.harvard.edu. (2007). Darwinian Fitness from http://www.mcz.harvard.edu/Departments/PopGenetics/pdf/2007_07_-_Darwinian_fitness.pdf
Metzler, Katy. (n.d). Selective Pressure: Definition & Example from http://study.com/academy/lesson/selective-pressure-definition-example-quiz.html
Sheldrake, Rupert. (2015). Darwinian Inheritance and Evolution of Evolutionary Theory from