Introduction
Evolution is “descent with modification” (Charles Darwin). The questions evolution tries to address include: why are so many types of species on our plant? Where did they come from? How is it that they all appear to be so different but in fact are all somewhat related? The study on evolution has a tremendous impact on your life. For example, it can explain why doctors do or do not give antibiotics when you are sick, it can also explain the HIV world crisis.
The Father of Evolution: Charles Darwin
Theory of Evolution was first described by Charles Darwin. To understand “descent with modification”, one needs to understand 1) the idea that current day organisms arose from older ancestral species over time; 2) Modification is a mechanism or process of interaction between the environment and an organisms to select for inheritable traits. Natural selection is one important mechanism of modification. If a species survives long enough, it has been selected naturally. The survival depends on an organisms fit to the environment. In another word, the organism best fit to the environment survive to propagate—this is called “survival of the fittest”.
Natural Selection
Natural selection is a process in which some organisms die and some survive based on their natural variation and how successful they are in their environments. The ones that survive inherit the traits. Over time, the inherited traits of the more fit organisms becomes standard, and known as an adaptation.
Speciation
New species originate in the process of evolution. Speciation event occurs when members of a new reproductive community no longer interbreed with their ancestral population as a result of isolation and subsequent accumulation of adaptations to their new environment. Evolution includes multiple speciation events over time, which can be depicted with a phylogenetic tree.
Evidence of Evolution
Evidence for evolution includes the fossil record, taxonomy, genetic evidence, and homologous structures. The fossil record shows organisms which might be ancestors of organisms today, changing slowly over time. Taxonomy shows organisms that are grouped together according to evolutionary similarities. Genetic evidence shows that many organisms have common DNA patterns. Homologous structures suggest that organisms came from similar ancestors because they have very similar bone structures.
Genetic Variation
Natural variation is the differences among individuals within a species. Genetic variation can come from changes in DNA, which occurs during mutations or meiosis.
Hardy-Weinberg Equilibrium
Equilibrium occurs when natural selection cannot take place, and therefore the genes in the population remain constant. Equilibrium occurs when there is a large, randomly mating population, where no one enters or leaves, mutation does not occur, and natural selection does not take place.
