The theory of evolution is a scientific theory of the origin of species of plants and animals, including humans. Charles Darwin began developing this theory during a boat voyage in 1838. In 1859, Darwin published On the Origin of Species, a book that explained natural selection and the theory of evolution in detail. On the Origin of Species was so successful people referred to the theory of evolution as Darwinian Evolution. (Sokal) There are five main ideas behind the theory of evolution. These are evidence of evolution, natural selection, genetic change and equilibrium, reproductive isolation and patterns of evolution. Together, these five concepts validate and illustrate the theory of evolution. To understand the theory of evolution, each concept can be researched and explained in detail.
Evidence to support the theory of evolution comes from many different areas of scientific research. These areas of scientific research include biogeography, homology, and the fossil records. Research from these three different fields provides evidence that proves the descent of modern species from ancestral species through documented variation in their genetic makeup. (Anti Essays, 2013)
Biogeography is the idea that organisms are geographically distributed throughout the world. (Anti Essays, 2013) The existence of a singular continent, called Pangaea, that broke into multiple different landmasses and drifted apart to form the different continents known today, a process referred to as continental drift, is generally accepted among scientists. Continental drift is cited as the reason organisms that appear to be closely related have been found in distant locations separate from each other, locations these organisms would have had no way of traveling to. An example of this occurrence can be seen by comparing today’s two species of the ostrich and the emu. The ostrich and the emu are remarkably similar in genetic make-up, however the ostrich is native to Africa while the emu is native to Australia. It is theorized that millions of years ago the ostrich and the emu were the same species. Continental drift seperated and relocated the animals on different landmasses. The animals adapted to their new environments and over time evolved into the two separate species known today. Information such as this is how biogeography supports Darwinian evolution. (Anti Essays, 2013)
Homology is a second scientific field where supporting evidence for the theory of evolution is found. Homology is when a characteristic of related species is similar in structure, but has a difference in its function. (Anti Essays, 2013) At the base molecular level, the genetic language of DNA and RNA is the same. All species share cytosine, guanine, adenine, thymine, and uracil, simply in different combinations. Homology can be easier seen by comparing a human arm, a dog’s leg, a bird’s wing, and a shark’s fin. The bone structure of all four are similar throughout the appendage, however each appendage has a different purpose. The arm is for lifting, the dog’s leg for walking, the bird’s wing for flying, and the shark’s fin is for swimming. (Anti Essays, 2013) The similarity illustrated in the field of homology provides support for the theory of evolution.
The second concept behind the theory of evolution is that of natural selection. Natural selection is paramount to the theory of evolution, along with the processes of mutation, migration, and genetic drift. (University of Berkeley, 2012) Thanks to the University of Berkeley’s website, Understanding Evolution, the process of natural selection can be understood through four steps. These four steps are variation in traits, differential reproduction, heredity, and the end result. On the website, beetles are used as the example. Variation of traits are seen in beetles when it is observed that they can be either green or brown in color. The second step, differential reproduction, addresses the environment’s inability to support unlimited population growth. In other words, all beetles cannot be allowed to freely reproduce. Green beetles are more noticeable by birds and tend to get eaten before they have a chance to reproduce. Reproduction problem solved. The third step is heredity. Heredity simply means that offspring will share genetic traits with their parents. Brown beetles will have brown baby beetles. The end result of variation, differential reproduction, and heredity is that the population will sway to brown beetles, brown color having proved to be the more advantageous trait, and eventually green beetles will no longer exist within this group. (University of Berkeley, 2012)
The third main concept behind the theory of evolution is that of genetic change and equilibrium. Genetic equilibrium is a concept demonstrated by a mathematic formula of the allele pool equation as developed by Hardy and Weinberg. (Blamire, 2001) According to the Hardy and Weinberg formula, populations exist in a state of genetic equilibrium and exhibit no change, therefore no evolution. While some populations of species do exist in a state of genetic equilibrium for millions of years, it is the amount of deviation from a state of genetic equilibrium by which evolutionary change is measured. In order for genetic equilibrium to be met, five factors must be present. Reproduction must be totally random, there must be no gene flow, populations must be large, no mutations, and no natural selection. (Blamire, 2001) When there is a change to any of these five conditions, as evident in our world, evolution takes place.
Reproductive isolation is the concept that individuals from a species must be completely isolated into separate groups in order for speciation, the development into a new species, to take place. If individuals are able to contact each other, there is nothing to prevent breeding and so traits will continue to mingle, preventing speciation. (University of Berkeley, 2012) Factors that contribute to speciation are a result of natural selection, sexual selection, or genetic drift. Barriers that will serve to isolate individuals from their original species include the evolution of different mating location, mating time, or mating rituals, a lack of fit between sexual organs, or offspring sterility. (University of Berkeley, 2012)
The final concept behind the theory of evolution is that of patterns of evolution. Through the process of natural selection, new species are ultimately formed. Often, many separate species will evolve from the same ancestral species. This evolutionary pattern of many species evolving from a single, common ancestor species is referred to as adaptive radiation. (Earlham) Adaptive radiation occurs when one species invades an isolated region containing few species to compete with and interbreed. Adaptive radiation itself is an example of divergent evolution, the process where related species become increasingly dissimilar. It also occurs that unrelated species in different environments will become increasingly similar. This is called convergent evolution. (Earlham) Finally there is co-evolution, a process where multiple species in close interaction with each other experience joint change. This can occur among predators and their prey, parasites and their hosts, and plant-eating animals and the plants they eat.
Together, these five concepts illustrate the theory of evolution in our world.
Anti Essays. (2013). Evidence of Evolution. Retrieved February 4, 2013, from Anti Essays: http://www.antiessays.com/free-essays/102500.html
Blamire, J. (2001). Genetic Equilibrium. Retrieved February 4, 2013, from Exploring Life @ Bio dot Edu: http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/C21_Equilibrium.html
Earlham. (n.d.). Patterns of Evolution. Retrieved February 4, 2013, from Bioweb: http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html
Sokal, R. &. (n.d.). The biological species concept: A critical evaluation. The American Naturalist , 104 (936): 127-153.
University of Berkeley. (2012). Natural Selection. Retrieved February 4, 2013, from Understanding Evolution : http://evolution.berkeley.edu/evolibrary/article/evo_25
University of Berkeley. (2012). Reproductive isolation. Retrieved February 4, 2013, from Understanding Evolution: http://evolution.berkeley.edu/evolibrary/article/evo_44