.. observed that wild animals and plants showed variations just as domesticated animals and plants did. He filled his notebooks with records of height, weight, color, claw size, tail length, and other characteristics among members of the same species. He also observed that high birthrates and a shortage of lifes necessities forced organisms into a constant "struggle for existence," both against the environment and against each other. Plant stems grow tall in search of sunlight, plant roots grow deep into the soil in search of water and nutrients. All that evidence is what supported Darwins theory about natural selection.

Peppered moths provide an example of natural selection in action. Peppered moths spend most of their time resting on the bark of oak trees. In the beginning of the nineteenth century, the trunk of most peppered moths in England were light brown speckled with green. There were always a few dark-colored moths around, but light colored moths were the most common. Then, the Industrial Revolution began in England and pollution stained the tree trunks dark brown.

We will write a custom essay sample on

Evolution specifically for you

for only $13.90/page

Order Now

At the same time, biologists noticed that dark-colored moths were appearing. The evolutionary hypothesis suggested that birds were the main reason. Birds are the major predators of moths. It is a lot harder for birds to see, catch, and eat moths that blend in with the color of the tree bark than it is for them to spot moths whose color makes a strong contrast with the tree trunks. The moths that blend in with their background are said to be camouflaged.

As the tree trunks darkened, the dark-colored moths were better camouflaged and harder to spot, having a better condition for survival. This hypothesis was not enough, and more experiments had to be made. A British ecologist, called Kettlewell, prepared another test for this hypothesis. He placed equal numbers of light and dark colored moths in two types of areas. In one area, trees were normally colored.

In the other area, they were blackened by soot. Later on, he recaptured, sorted, and counted all the moths he could, which were marked earlier by him. Kettlewell found that in unpolluted areas, more of his light-colored moths had survived. Kettlewell showed by his experiments that the moths that were better camouflaged had the higher survival rate. In conclusion, when the soot darkened the tree trunks in an area, natural selection caused the dark-colored moths to become more common. Kettlewells work is considered to be a very good classic demonstration of natural selection in action. All organisms share biochemical details. All organisms used DNA and RNA to carry information from one generation to another and to control growth and development. The DNA of all Eukaryotic organisms always has the same basic structure and replicates in the same way.

The RNAs of various species might act a little differently, but all RNAs are similar in structure from one species to the next. ATP is an energy carrier that is also found in all living systems. Also many proteins, such as cytochrome c, are also shared by many organisms. This molecular evidence has made it possible to make precise comparisons of the biochemical similarities between organisms. Scientists also noticed that embryos of many different animals looked so similar that it was hard to tell them apart. Embryos are organisms at early stages of development.

These similarities show that similar genes are present. The fact that early development of fish, birds, and humans is similar shows that these animals share a common ancestor, who had a particular gene sequence that controlled its early development. That sequence has been passed on to the species that descended from it. In the embryos of many animals the limbs that develop look very similar. But as the embryos mature, the limbs grow into arms, legs, flippers that differ greatly in form and function.

These different forelimbs evolved in a series of evolutionary changes that altered the structure and appearance of the arm and leg bones of different animals. Each type of limb is adapted in a different way to help the organism survive in its environment. Structures like these, which meet different needs but develop from the same body parts, are called homologous structures. This is all additional evidence of descent from a common ancestor. There are other theories for the origin of species including special creation and panspermia.

Special creation involves humans. Many people believe that humans were created by God; so the theories of evolution go against their religions especially why they do not see Gods hands in the process. As for panspermia, it suggests that life could have originated somewhere else and came to us from space. This might be possible but there is actually no supporting evidence for it. Paleontology has also played a big role in the study of evolution.

Over the years, paleontologists have collected millions of fossils to make up the fossil record. The fossil record represents the preserved history of the Earths organisms. Paleontologists have assembled great evolutionary histories for many animal groups. An example would be looking at probable relationships between ancient animals whose evolutionary line gave rise to todays modern horse. The fossil record also tells us that change followed change on Earth.

Scientists can use radioactivity to determine the actual age of rocks. In rocks, radioactive elements decay into non-radioactive elements at a very steady rate. Scientists measure this rate of radioactive decay in a unit called a half-life. A half-life is the length of time required for half the radioactive atoms in a sample to decay. Each radioactive elements has a different half-life. Carbon-14 is particularly useful because it can be used to date material that was once alive.

Because carbon-14 is present in the atmosphere, livings things take it into their bodies while theyre alive. So the relative amount of carbon-14 in organic material can tell us how long ago this material stopped taking in new carbon into its system. That was the time it died. Then, a graph is used to determine the time. This is the way scientists can deduce the approximate age of materials based on a simple decay curve for a radioisotope.

In organisms, variations in specific molecules can indicate phylogeny; and biochemical variations can be used as an evolutionary clock. Phylogeny is the line of evolutionary descent. Biochemistry can be used to support other evidence about revolutionary relationships, and it can be very simple. Scientists study similar molecules in different species and determine how much difference there is between the molecules. The more difference there is, the longer the time-span since the two species shared a common ancestor. The most commonly used substances in this technique are hemoglobin , cytochrome c, and nucleic acids.

Hemoglobin is suited to studying closer related organisms that contain hemoglobin. Cytochrome c has been used to compare groups that are more different. The results from comparative biochemistry lone do not prove anything, but they confirm data found using other methods. Together, they become convincing. Today, the theory of evolution is generally considered to be the most important fundamental concept in the biological sciences. Nearly all scientists support it.

However, large numbers of people opposed the theory when it was introduces. Still, some people do not accept it today. Bibliography 1. Arms, Camp. Chapter 17, "Evolution and Natural Selection," Chapter 21, "Origin of Life." Biology. Bonnie Boehme. Fourth Edition.

The United States of America. Harcourt Brace College Publishers; 1995. Pages 352-372, 440-455 2. Curtis, Barnes. Chapter 46, " Evolution: Theory and Evidence," Chapter 48,"Natural Selection," Chapter 49 "On the Origin of Species." Biology. Sally Anderson. Fifth Edition.

New York, USA; Worth; 1989: Pages 961-973, 991-1029 3. Roberts, M.B.V. Chapter 34, " Evolution in Evidence," Chapter 35,"The Mechanism of Evolution," Biology. Fourth Edition. Surrey, UK; Nelson; 1986: Pages 560-616 4. The World Book Encyclopedia.

World Book, inc. London: v.6; Pages 406-413 "Evolution". 5. Encyclopedia Britannica. Encyclopedia Britannica, inc. Chicago: v.4; Page 623 "Evolution".

6. http://www.talkorigins.org/origins/faqs-evolution. html 7. http://www.wku.edu/~smithch/index1.htm 8. http://bioinfo.med.utoronto.ca/~lamoran/Evolution home.shtml.