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.
Theory of Evolution
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”.
Origin of species
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. A phylogenetic tree shows a relationship between ancestor and descendant, i.e., the pattern of evolution. Most often the pattern is branching; each branch containing the oldest ancestor in that line plus all of its descendants.
Scientific Steps to Darwin’s Theory
Observation: 1) struggle of existence -- Reproducing organisms will produce more offspring than the environment can support if all offspring survive to reproduce; 2) within any given population, there is a range of individual, heritable characteristics; 3) survival depends on an organism’s inherited traits. Hypothesis: 1) Attributes that lead to a better fit to an environment lead to greater chance for leaving behind offspring; 2) Disproportionate reproductive success among population members lead to gradual change in traits of that population. Hypothesis Testing: 1) fossil record; 2) comparative anatomy and embryology; 3) Independent traits; 4) DNA similarity.
Evolutionary Theory Today
Darwin thought evolution is a gradual process, today’s evidence suggest that 1) evolution may follow a spurt and plateau pattern (punctuated equilibrium); 2) Changes of ecosystem play bigger roles in stimulating accumulation of new species then once thought; 3) other mechanisms of species modification have been discovered such as gene flow and non-random mating, although natural selection remains the major player.
