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Principles of Evolution

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1 Principles of Evolution
Chapter 10 Principles of Evolution

2 Section 10.1: Early Ideas About Evolution
Evolution- the process of change over time by which descendents come to differ from their ancestors. The man given credit for the findings on evolution is Charles Darwin; however, he wasn’t the first to talk about it. The concept had been discussed for more than 100 years.

3 Section 10.1: Early Ideas About Evolution
Carolus Linnaeus- Developed a classification system for all types of organisms in the 1700’s. He believed organisms changed through hybridization which was crossing of genes. He believed this produced new species. Species are groups of organisms that can reproduce and have fertile offspring.

4 Section 10.1: Early Ideas About Evolution
Georges Leclerc De Buffon- proposed that species shared ancestors instead of rising separately. He also argued the earth was more than 6000 years old.

5 Section 10.1: Early Ideas About Evolution
Erasmus Darwin- Grandfather of Charles Darwin. He concluded that more complex life forms came from less-complex forms.

6 Section 10.1: Early Ideas About Evolution
Jean-Baptiste Lamarck- Early 1800’s proposed that all organisms evolved towards perfection and complexity. He also believed that if you stopped using part of your body, you would lose it over time and that characteristic could be passed on.

7 Section 10.1: Early Ideas About Evolution
For Darwin’s theory, the age of the Earth was the key issue. They belief of that time was the Earth was about 6000 years old. Early scientists who studied fossils believed it was much older.

8 Section 10.1: Early Ideas About Evolution
Scientists who believed that Earth was relatively young believed in catastrophism, which states that natural disasters create very quick and sudden changes. Scientists who believed the Earth was old believed in gradualism, which argued that things change over long periods of time slowly. Geologists James Hutton studied the Earth and decided things like “The Grand Canyon” couldn’t have formed that quickly.

9 Section 10.1: Early Ideas About Evolution
One of the leading proponents of Earth being old was economist Charles Lyell. Lyell took Hutton’s gradualism concept and expanded it to unifomitarianism. This belief stated that processes that shape the Earth are uniform throughout time. Lyell and Hutton gave Darwin the information he needed to prove evolution as a theory.

10 Section 10.2: Darwin’s Observations
As Darwin traveled and observed, he was shocked by the number of different traits among similar species. When Darwin visited the Galapagos Islands off the coast of South America, he noticed much variation among species. He also noticed these variations suited the environment these animals were living in.

11 Section 10.2: Darwin’s Observations
For example: Certain tortoises that have long necks and legs live on islands with tall plants. Tortoises with short legs and necks lived on islands that grew low vegetation and lots of ground moss.

12 Section 10.2: Darwin’s Observations
Another example was finches. Finches with strong, thick beaks lived in areas that had large hard-shelled nuts and those finches with short delicate beaks lived on islands rich in insects and fruits.


14 Section 10.2: Darwin’s Observations
Was this just a coincidence or was there something happening to the species? Darwin determined that organisms must somehow be able to adapt to their environment. An adaptation is something that allows an organism to better survive in its’ environment.

15 Section 10.2: Darwin’s Observations
On his voyages, Darwin found fossil evidence of organism’s changes. He found fossils similar to living organisms today and also found sea-life fossils on tops of mountains. This meant that at one time the mountain was under water and it had to take a long time for the water to fall and mountain to rise. To Darwin, this proved that the Earth was old!

16 Section 10.3: Theory of Natural Selection
Darwin came back after his voyages and spent 20 years researching about his findings. He was especially influenced by his homeland of England. He was very intrigued by farmers and breeders. Darwin noticed that a lot of domesticated plants and animals showed many different traits that were not shown in the wild. What was happening was farmers were selecting which organisms would reproduce so the best traits would be passed on.

17 Section 10.3: Theory of Natural Selection
When humans select which organisms breed, this is called artificial selection. Farmers only let big cows mate with big cows because they are paid by the pound.

18 Section 10.3: Theory of Natural Selection
Darwin concluded that something like this must occur in nature. Obviously, humans have nothing to do with wildlife interbreeding; however, Darwin believed that some type of selection occurred. Darwin termed this natural selection.

19 Section 10.3: Theory of Natural Selection
Natural selection is a mechanism by which individuals that have inherited beneficial characteristics produce more offspring than other organisms do. In natural selection, the environment is the selective agent.

20 Section 10.3: Theory of Natural Selection
Another important piece of information that Darwin used came from an English Economist Thomas Malthus. Malthus had proposed that resources such as food, water, and shelter were natural limits on population growth. Darwin took this information and reasoned that this affected species in nature. He called this the “struggle for survival”

21 Section 10.3: Theory of Natural Selection
If resources are limited and organisms have more offspring than can survive, Darwin wanted to know which ones survived and why? Darwin summarized that the answer was in the variation within a population. A population is a group of individuals that lived in the same area.

22 Section 10.3: Theory of Natural Selection
Darwin figured out that variation in traits were well suited for their particular environment. He called this “Descent with Modification”. Darwin finally put all his findings together. He published a book called “On The Origin of Species By Means Of Natural Selection”.

23 Section 10.3: Theory of Natural Selection
In Darwin’s book there are 4 main principles: Variation: The differences that exist in every population are the basis for natural selection. Differences that are best suited for their environment get passed on to offspring.

24 Section 10.3: Theory of Natural Selection
In Darwin’s book there are 4 main principles: 2) Overproduction: More offspring are produced that can possibly survive. This creates competition between offspring for resources.

25 Section 10.3: Theory of Natural Selection
In Darwin’s book there are 4 main principles: 3) Adaptation: Most times variation allows individuals to survive better in the environment that they live. More successful individuals are “naturally selected” to live longer and produce more offspring.

26 Section 10.3: Theory of Natural Selection
In Darwin’s book there are 4 main principles: 4) Descent with Modification: Over time, natural selection will result in species with adaptations that suit their environment. Jaguars: Teeth and jaw size


28 Section 10.3: Theory of Natural Selection
Adaptation leads to fitness. Fitness is the measure of the ability to survive and produce more offspring relative to other organisms. The fitness only remains if the environment remains constant. As the environment changes, the traits that were once more favorable, may become less favorable and new adaptations will be needed.

29 Section 10.4: Evidence of Evolution
Darwin found many sources of evidence for evolution: Fossils- fossils found in older layers of rock differed from fossils in younger layers of rock. Geography- similar organisms were found on different mainlands. Embryology- looking for similar development in the womb. Anatomy- Some of Darwin’s best evidence came from comparing body parts of different species.

30 Section 10.4: Evidence of Evolution
Anatomy (continued) Homologous structures are features that are similar in structure but have different functions in different organisms. For example, the human hand, mole feet, and a bat’s wing all have very similar structures, but different functions. To Darwin, this proved common ancestory.

31 Section 10.4: Evidence of Evolution
However, organisms can have structures that are used for similar purposes but are not anything alike structurally. This is called analogous structures Example: a fly’s wing and a bat’s wing

32 Section 10.4: Evidence of Evolution
Some organisms still show signs of structures that are no longer used for their original purpose or lack any usefulness at all. These are called vestigial organs. Vestigial structures are remnants of organs or structures that had a function in early ancestors.

33 Section 10.5: Evolution Today
Fossils provide a record of evolution. The study of fossils or extinct organisms is called paleontology. Fossil evidence is not complete because most organisms die and decay; however, no scientist has ever found a fossil that contradicts evolution. Paleontology was a new science in Darwin’s time. Darwin worried about gaps in the fossil record; however, since his time many of those gaps have been filled.

34 Section 10.5: Evolution Today
Scientist use DNA sequence analysis and protein comparisons to link past fossils to today’s organisms. Scientist still today actively try to find more pieces of the puzzle relating to evolution.

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