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Transcript
Chapter 10 Principles of Evolution 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. 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. Section 10.1: Early Ideas About Evolution • Georges Leclerc De Buffonproposed that species shared ancestors instead of rising separately. • He also argued the earth was more than 6000 years old. Section 10.1: Early Ideas About Evolution • Erasmus Darwin- Grandfather of Charles Darwin. • He concluded that more complex life forms came from lesscomplex forms. 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. 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. 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. 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. 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. 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. 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. 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. 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! 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. 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. 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. 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. 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” 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. 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”. Section 10.3: Theory of Natural Selection • In Darwin’s book there are 4 main principles: 1) 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. 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. 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. 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 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. Section 10.4: Evidence of Evolution • Darwin found many sources of evidence for evolution: 1) Fossils- fossils found in older layers of rock differed from fossils in younger layers of rock. 2) Geography- similar organisms were found on different mainlands. 3) Embryology- looking for similar development in the womb. 4) Anatomy- Some of Darwin’s best evidence came from comparing body parts of different species. 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. 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 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. 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. 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.