Darwin's Theory of Evolution

Describe Darwin’s theory of evolution by natural selection.
Darwin’s theory of evolution by natural selection is a species adaptation to its environment and the environment’s impact to the species over time. Traits that benefit the survival of the species within a specific environment pass to offspring because members of the population that have the beneficial traits are more likely to survive and reproduce. In order for a change to be evolutionary it must be genetic and on a hereditary level. The change occurs from generation to generation and over time impacts the entire population. Evolution by natural selection can impact a species to the point of varying so much from its original traits it is now a new species. It can also force a species into extinction.
A population, which is defined as “a group of individuals of the same species living in the same place at the same time”, changes over time as it evolves. (Simon pg. 245) Two observations were made by Darwin as well as other naturalists. 1) Most species have more offspring than can be sustained by their surrounding environment. This creates a “struggle for existence” that eliminates the least adaptable within the species. Numbers dwindle due to members of a species freezing, disease, becoming prey to predators, being unmated or being unable to reproduce. Those who are more adaptable to the environment’s temperature, have an allele which codes for an enzyme that fights a disease, have the coloring that camouflage their presence or are fertile, are more likely to survive. 2) Traits of members of a population can vary but are more similar between offspring and their parents and siblings. It supports the belief that traits are directly inherited from parent to child.
Geography has an impact on evolution in that the resources surrounding a population can impact those who are able to survive. The plants animals and insects available as food can impact those successful in feeding and what characteristics are conducive to feeding. Over time those who are successful have offspring and those who are not successful die off. Therefore the hereditary traits of the successful members of the population continue to inhabit and reproduce within that environment. Narrowing down the beneficial features until after many generations almost all of the population contains these beneficial features. A species that started on a mainland and spread to two different islands can overtime adapt in their traits so much as to now qualify as a new species.
Explain how this theory was a major advance over prior ideas as to how organisms changed over time.
Darwin’s theory was a major advance over prior ideas as to how organisms changed over time. Greek philosopher Aristotle and Judeo-Christian writing of the Bible’s Book of Genesis expressed a belief that species were fixed and did not change. This belief held despite a growing number of naturalists who uncovered fossils that showed various species with characteristics identical or close to species known at the time. They began to document what was same and what was different.

In the early 1800s naturalist Jean-Baptiste Lamarck came to the conclusion that these documented differences proved that “life evolves” (Simon pg. 246). This was supported by the discovery fossils that were of species that no longer existed. This brought about the idea of extinction. That a species can exist and then die out for unknown reasons brought about a new way of thinking in terms of a species. Lamarck believed that the use or non-use of certain trait could impact offspring. While this theory was proven incorrect it was the spring board for Darwin’s theory.
Darwin took three observations from the findings of earlier naturalists. 1) life is diverse 2) similarities among organisms allowed them to be classified in groups within larger groups or populations 3) the ways in which organisms are suited to their various environments. In 1831 he took a trip on the Beagle to South America. He was specifically intrigued but the variety of the species found in the Galapagos Islands that were unknown to him. He was also influenced by reading the new geography book “Principles of Geology”, by Scottish geologist Charles Lyell. All of these influences and observations were the basis of a long essay in the early 1840s.
Darwin feared his essay was so far a jump in beliefs that he did not publish or share his finding with the science community. This opinion changed in the mid-1850s when naturalist Alfred Wallace, doing research in Indonesia, came up with beliefs identical to Darwin’s. Their findings were released together and Darwin’s essay became the basis for “On the Origin of Species by Means of Natural Selection”.

Give evidence in support of evolution and describe the driving forces for evolutionary change.
If the environment is the driving force of a species adaptation and evolution then technology is the driving force of evolutionary change. As the world expands its technological knowledge we constantly impact the environment and nature. “Acid rain, deforestation, global climate change, nuclear accidents, toxic wastes, and extinction of species are just a few of the repercussions of more and more people wielding more and more technology.” (Simon pg. 18) Pollution and widespread exposure of the environment to chemicals (intentionally and unintentionally) has had an impact on plants, animals and insects.
An example of evolution in action is the impact of the use of DDT, a commonly used pesticide. In populations where many humans were dying from malaria, a disease contracted and spread by mosquito bites, areas were sprayed with DDT to kill off the mosquitos. The relief was short lived. After some time the mosquito populations grew back and are now resistant to the pesticide. What was discovered was that some of the initial population contained an allele. A chromosome that produces an enzyme that allowed them to be resistant to DDT. Since these resistant mosquitos were the only ones to survive they reproduced with other resistant mosquitos. The population rebounded and was then fully resistant due to all of the offspring coming from resistant parents. The elimination of the mosquitos that could be impacted strengthened the population in the end.
Another example of evolution at work is the flu virus. The flu virus is a pathogen that as it circulates throughout the world’s population changes and adapts. The flu virus adapts and evolves with every exposure to a human. The vaccine for the flu must be modified every year as the characteristics and the various strains of the flu increase. Bacteria and pathogens have a short life cycle. Some bacteria only live for 15 minutes. “In each pathogen generation, new mutations and gene combinations are generated that then pass through the selective filter of our drugs and immune response” (Understanding Evolution).
Another example of evolution at work if the study done on the flat tailed horned lizard of the American Southwest. The lizard’s main predator is a shrike which strikes the lizard’s neck directly behind his skull where he severs its spine. The lizard’s only protection from attack is to use the horns on its head to strike back at the shrike before it has the opportunity to puncture its neck. Scientists believed that if they examined the lizard they would find that the horns on the head of the living would be longer than those of those killed. They measured the horns of 29 killed and 155 live lizards. The average length of the live lizards was about 10% greater than those of those killed. The trait of having longer horns assists in its survival. The trait was measurable and observable and proves the impact to the evolution of the flat tailed horned lizard.

References
Simon, Reece, Dickey, E. (2012). Campbell Essential Biology with Physiology (4th ed). Pearson Learning Solutions. Retrieved from http://digitalbookshelf.southuniversity.edu/books/9781256902089/id/ch13bx3
TIME Big Book of Why. (2011). "What is Charles Darwin 's theory of evolution?”. McClatchy - Tribune News Service.
Understanding Evolution. (1998). “Relevance of Evolution: Medicine”. Retrieved from http://evolution.berkeley.edu/evolibrary/article/0_0_0/medicine_02

References: Simon, Reece, Dickey, E. (2012). Campbell Essential Biology with Physiology (4th ed). Pearson Learning Solutions. Retrieved from http://digitalbookshelf.southuniversity.edu/books/9781256902089/id/ch13bx3 TIME Big Book of Why. (2011). "What is Charles Darwin 's theory of evolution?”. McClatchy - Tribune News Service. Understanding Evolution. (1998). “Relevance of Evolution: Medicine”. Retrieved from http://evolution.berkeley.edu/evolibrary/article/0_0_0/medicine_02