Variation - is the differences that exist between individuals.
Intraspecific variation - Variation within a species.
Interspecific variation - Variation between different species.
Continuos variation - Variation within a range of numbers (e.g quantative data such as weight or height).
Discontinuos variation - Variation within distinct categories (e.g qualitative data such as blood group or gender).
Evolution: Causes of variation
Variation can be caused by both genetic and environmental factors, or a combination of both factors.
Genetic factors - Individuals within a species have different alleles which determine the genotype and phenotype of an organism. For example, variation in eye colour is caused by genetic factors.
Environmental factors - Variation can be caused by the differences in the environment such as climate or food. These characteristics can change over time.
Behavioural adaptations - The ways in which an organism acts to increase its chances of survival in its environment.
Physiological adaptations - The ways in which the chemical processes in an organism increase its chances of survival in its environment.
Anatomical adaptations - The ways in which the structural features of an organism increase its chances of survival in its environment.
Evolution: Natural selection
1) Organisms produce more offspring than survive.
2) There is variation in the characteristics of members of the same species.
3) Some of these characteristics can be passed on from one generation to the next.
4) Individuals that are best adapted to their environment are more likely to survive.
Natural selection - An individual within a species may show a different characteristic that will arise due to a random mutation or simply because it is a variation within its phenotype. If the characteristic proves to be useful, the individual will survive and go on to reproduce, passing on this characteristic to its offspring. Over time and several generations, this desired characteristic will be more common in the population as the alleles that cause it will be more widespread.
Scientists can prove Darwin's theory of natural selection through various pieces of evidence:
Fossil records - Fossils are the remains of organisms that are preserved in rocks. By arranging fossils in chronological order, scientists can observe gradual changes in organisms over time.
DNA evidence - Scientists can use DNA sequencing to identify common ancestors, as closely related species will have more similar DNA.
Molecular evidence - Scientists can compare the similarities between molecules such as proteins in different organisms. The more similar the amino acid sequence of two organisms is, the more closely related they are and the more recently they diverged away from each other.
Evolution: Speciation and Resistance
Speciation - The formation of new species through the procewss of evolution.
Allopatric speciation - When the geographical isolation of a population of a species causes a new species to form due to different selection pressures in the area.
Sympatric speciation - When genetic drift causes a new species to form.
Antibiotic resistance - Natural selection has happened within bacteria populations, making them resistant to antibiotics and other drugs. This has severe implications for humans as we will run out of antibiotics to treat patients with, meaning there will be no way of curing patients. We will have to invest lots of money in developing new antibiotics, which could take many decades.
Pesticide resistance - Natural selection has happened within insect populations, making them resistant to pesticides. This has severe implications for humans as farmers will struggle to keep insects from eating crops, meaning food sources will diminish.