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Chapter 23 The Theory of Evolution

Page history last edited by Nicole Lee 13 years ago

The Theory of Evolution

     Many people ponder the question as to how humans got to where we are today.  How were we made?  Did God just magically clap his hands and we appeared on the face of this Earth?  Are we essentially evolutionary forms of monkeys and chimpanzees?  Were we formed from tiny bacteria that formed a human?  Evolution is a very controversial subject because it can cause conflict between both religious beliefs and the facts of science. 

                In the 1600’s in Europe, there was a revolution that created the basis of both empirical and scientific thought.  Let’s start off by defining the basics!  Empirical thought does not rely on understanding life from a nonphysical or spiritual view, but rather an observation to form an idea or hypothesis.  This shift was crucial because it encouraged scholars to look for reasoning behind a phenomenon rather than relying on myth and spiritual beliefs.

                So who was the first scientist to carry out a thorough study of the living world?  John Ray, an Englishman accomplished this and also developed an early classification system for animals and plants.  He based his classification off of anatomy and physiology.  From this, Mr. Ray was able to create the basics of a species.  He noted that organisms of one species do NOT interbreed with members of another (Ex: dogs don’t breed with cats; lamas don’t breed with beta fish) and used this observation as the basis of his classification system.  A Swedish man named Carolus Linnaeus followed up on Mr. Ray’s scientific discoveries.  Together these two men contributed and boosted the development of the evolutionary theory from their systematic classification of plants and animals.  Their discoveries greatly aided scholars to understand and be able to compare and contrast living organisms from one another.

                A man named George Buffon later proposed that all living organisms change through time.  Around this same era, a man named Jean- Baptiste Lamarck suggested that there is a very close relationship between both variation and evolution.  Lamarck utilized fossils to support his idea and from these, he learned that some species remained the same over the past millennia while others changed at an incredible pace.  From this observation, Lamarck created the hypothesis that species change over time and over many different generations due to the need of adaption to the environmental shifts.  Lamarck believed that all of the living organisms on this earth evolve in an upward direction, and according to him, all organisms change their lifestyles to correlate with the environmental changes (such as warmer climate, or flooding in the environment).  This belief leads us to our next extremely important term inheritance of acquired characteristics!  This is the belief that behavioral changes modify traits of the organism, and these modified traits would later be passed down and inherited to the offspring.  Although Lamarck’s ideas are now rejected after further review and research, his contributions to the scientific community greatly promoted the idea of evolutionary change.

                Now we will advance to our next important man of this time, Erasmus Darwin (Charles Darwin’s father) who was not only a physician but a plant biologist as well as a poet.  Mr. Erasmus Darwin knew that modern species differed from similar types of fossilized organisms and he also observed how plant and animal breeders utilized methods of breeding to change traits of domesticated species.  Darwin suggested that every species has derived from a pre- existing species.

                Through Charles Darwin’s educational background with geological and biological processes, he contributed to the theory that existing species must have evolved in some way from a pre- existing species.  During this point in time two major geological hypotheses in the early 19th century. 

  1. Catastrophism- this hypothesis was proposed by a man named Georges Cuvier and was used to explain the age of the earth.  He suggested that the Earth (at the time) was only 6,000 years old and that only catastrophic events have changed the overall geological structure.  This hypothesis was supported by religion.
  2. Uniformitarianism- proposed by a man named James Hutton (later to be popularized by a man named Charles Lyell).  This hypothesis suggested that changes in Earth are caused by recurring events

Now moving on from the two hypotheses, Darwin’s ideas were greatly influenced by those of Hutton and Lyell who believed erosion existed in the past and they were the first to propose the age of the earth, and also a paper published in 1789 called Essay on the Principle of Population by Thomas Malthus.  This paper suggested that only a fraction of any population will survive and reproduce.

                Darwin’s ideas were also mostly influenced through his own experiences and what he observed throughout his years of studies.  One of his most important voyages was aboard the ship the Beagle to map the coastline of Southern America to take oceanographic measurements, record the weather, geological features, animals, plants, fossils, rocks, indigenous people, and minerals.  While on his voyage, Darwin made many crucial observations especially about different islands he visited, however these observations were one of the least most important of all of his knowledge.  At first, Darwin observed several species of finches on the Galapagos Islands; he thought that the birds were various species of blackbirds, grosbeaks, and finches.  However, another scientist came along and corrected his error, seeing that the birds were truly all finches.

                Through the birds that Darwin examined, we now know that all finches evolved from a single species that is similar to the grassquit finch.  Once these birds have flown to the secluded islands, their bodies eventually adapt and change to fit the changes of the environment.  Their upgrades allow themselves and their generations to get the food they thrive for.  From his observations, Darwin published a book about it; and although some of his ideas were incomplete because of the genetic basis of traits was not understood at the time, his work still remains one of the most crucial contributions to the scientific community. 

Darwin hypothesized that existing life forms on our planet result from the modification of pre- existing life- forms, and also that existing life- forms on our planet result from the modification of pre- existing life forms.  He expressed those concepts of evolution as the theory of descent with modification through variation and natural selection.  From Darwin’s ideas, we can possibly see that evolution can occur from generation to generation due to two interacting factors known as genetic variation and natural selection.

  1. Genetic variation-the traits may occur among individuals of a given species that are then passed on to the offspring.  Now we know that variation is due to different types of genetic changes sometimes even caused from random mutations in genes.  Traits are assumed to be passed from parent to offspring.
  2. Natural selection- The process that eliminates those individuals that are less likely to survive and reproduce in a particular environment, while allowing other individuals with traits that confer greater reproductive success to increase in numbers.  Due to natural selection, certain traits that are favored by reproductive success become much more prevalent in a population.

As an example, observe a finch that migrates from the South American mainland to a distant island and view the similarities and differences between the finches.  In order to adapt to different food sources, the finch may eventually adapt to get a larger beak to obtain the seeds in an easier fashion.  If the finch does not change, natural selection may kick in if the bird cannot obtain food from its beak then it will die.  

     Darwin observed differences in birds and he noticed that their beak shapes differed between different types.  For example, a vegetarian finch has a crushing shaped beak so that it can easily crush seeds it wants to eat.  The beak is a bit rounded and slightly large to have the ability to crush larger seeds.  Another beak variation between the finches is the cactus finch that has a sharper, much thinner beak for probing for food in a cactus.  More in depth detail will be put into this subject in the Prezi presentation as well as the virtual lecture.


Useful Materials

This song is not only catchy but also informative.  The lyrics describe how evolution can be caused by gene deletion.  This video also shows possible routes in which evolution could have taken in order for us humans to be evolved this way.  


This video is similar to the first; however this video is more informative in the way that it goes into great depth on the reasoning behind evolution.  This video goes over some of the basic concepts of evolution and shows an animation of an example of a process in evolution.


This song is very catchy and informative.  The teacher sings about natural selection.  Just remember, you don't have to out that bear, you just have to outrun your friend.





This link leads viewers to an awesome game that deals with evolution.  This game is not only fun to play but it also teaches students some aspects of evolution and puts the knowledge people learn to work.  



This link leads viewers to an interesting site where they can read more about Darwin's experience on his Beagle voyage.  As a quick re- cap, remember that Darwin's Beagle voyage lasted about 5 years and from this experience he learned many new things, and he recorded much information of what he saw, especially the finches he observed.  This article is a little bit lengthy but worth the read.



This website helps viewers understand the process of evolution on a deeper level.  It has many interesting facts and contains a list of other sites that are useful for studying this topic.



This website has a quick overview of what evolution essentially is.  It is short, to the point, and contains useful links to other pages that cover evolution.


This is a lovely picture I borrowed from the book.  This shows the process in which it shows how finches that migrate from the South American mainland to a distant island change their beaks overtime accordingly with their environmental changes.


This picture previews the process of a giraffes neck elongating due to the 'need' of stretching their necks to reach leaves.  This was Lamarck's hypothesis as to how their necks got so long.  Lamarck's hypothesis was wrong.


This is just another helpful picture showing both Darwin's and Lamarck's theory as to why giraffe's necks are so long.


This is a cartoon showing how animals tried to evolve and if they could not, they would usually die.





Prezi Class Lecture




Virtual Lecture


^^This is my virtual lecture of this section the screen- o - matic thing wasn't working for me so i just used powerpoint.  To hear my voice please click on view slide show, turn your volume up, and tune in:) Thanks!

Comments (1)

Lauren Banjo! said

at 8:45 am on May 1, 2011

haha, funny cartoon

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