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Darwin’s theory of evolution

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1 Darwin’s theory of evolution
Searcy Ninth Grade Center  2014

2 15.3 Darwin Presents His Case

3 Darwin’s Findings After Darwin returned to England in 1836 he filled notebooks with his ideas about species diversity and the process that he would later call evolution. He did not rush to publish his ideas because they disagreed with the fundamental scientific beliefs of his day. He asked his wife to publish his ideas when he died. Play video

4 Wallace’s Essay In 1858, another naturalist, Alfred Russell Wallace wrote an essay describing his work in Malaysia that summarized the same ideas Darwin had been thinking about for 25 years.

5 Origin of Species Suddenly Darwin had incentive to publish the results of his work. In 1859 On the Origin of Species presented evidence and proposed a mechanism for evolution that he called natural selection.

6 Evolution is a THEORY A theory is a well-supported, testable explanation of phenomena that have occurred in the natural world, like the theory of gravitational attraction, cell theory, or atomic theory.

7 Keys to Darwin’s Theory
Genetic variation is found naturally in all populations.

8 Keys to Darwin’s Theory
Struggle for existence means that members of each species must compete for food, space, and other resources.

9 Keys to Darwin’s Theory
Some organisms in a population are less likely to survive.

10 Keys to Darwin’s Theory
Survival of the fittest organisms which are better adapted to the environment will survive and reproduce, passing on their genes.

11 Vocabulary Ability of an individual to survive and reproduce in its specific environment = fitness. Hmmm…

12 Vocabulary Any inherited characteristic that increases an organism’s chance of survival = adaptation.

13 What is Darwin’s Theory?
Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in their environment. How does it work? Descent with modification suggests that each species has descended with changes, from other species over time. This idea suggests that all living species are related to each other; and that all species, living and extinct, share a common ancestor.

14 Evidence of Evolution Artificial selection Fossil record
Geographic distribution Homologous structures Embryology DNA Visual record natural selection happening

15 Artificial Selection In artificial selection, nature provides the variation through mutation and sexual reproduction; and humans select those traits that they find important. Examples: cows bred to produce more milk; turkeys with more breast meat, etc.

16 Dogs: Artificial Selection
Saint Bernard – bred by monks around 1050 A.D. to rescue travelers of mountain passes in the Swiss Alps between Italy and Switzerland Chihuahua – bred from Techichi of Mexico by Mayans, had religious significance. Dachshund – bred in Germany as early as the 15th century to hunt badgers.

17 Artificial Selection

18 Proof of Evolution Fossil Record – Fossils are the remains of ancient organisms found in layers of rock in the Earth.

19 Proof of Evolution The layers of rock tell the history of the Earth, while the fossils found within the rock tell a history of life. The fossils are thought to be the same age as the rock they are found in.

20 Movement of Earth’s Crust
Earthquakes and volcanoes cause uplifting of the layers of the Earth, taking the fossils along. Sea Level Sedimentary rocks form in horizontal layers. When part of Earth’s crust is compressed, a bend in a rock forms, tilting the rock layers. As the surface erodes due to water, wind, waves, or glaciers, the older rock surface is exposed. Fish die in the ocean and are covered in sediment. Over time and under increasing pressure, the remains becomes fossilized Fossils of marine fish found on the mountain sides of southwest Wyoming, which at one time was covered by an inland sea

21 Transitional Fossils

22 Verifying Darwin’s Findings
If Darwin’s theory is correct, one would expect to find closely related yet different species living in a geographic region as they spread into nearby habitats and evolve… Tortoises adapted to different habitats as they spread from the mainland to the different islands. = Divergent Evolution = Adaptive Radiation.

23 Adaptive Radiation Intermediate vegetation Intermediate necks
Little vegetation Long necks Lots of vegetation Short necks

24 Adaptive Radiation The beaks of Galapagos finches have adapted to eating a variety of foods.

25 Verifying Darwin’s Findings
If Darwin’s theory is correct you would also expect to find different species living far apart in geographic regions with similar habitats becoming more alike as they adapt to similar ecosystems. Whales and sharks have a similar body design even though they are very different organisms (one is a fish; the other, a mammal) because they have independently adapted to living in a similar environment = Convergent Evolution.

26 Geographic Distribution
Beaver and capybara are closely-related species living in very different environments, while beaver and musk-rat are distantly-related species living in a similar environment. Differences between beaver and capybara show divergent evolution, while similarities between beaver and muskrat show convergent evolution. Differences between closely-related muskrat and coypu show divergent evolution, while similarities between distantly-related capybara and coypu show convergent evolution. Beaver NORTH AMERICA Muskrat Capybara SOUTH AMERICA Coypu Beaver and Muskrat Coypu and Capybara

27 Homologous Structures
Structures, like the limbs of vertebrates, look very different, but are made from the same bones, because they are made from the same clump of undifferentiated cells in the embryo.

28 Homologous Structures
Turtle Alligator Bird Mammal Ancient lobe-finned fish

29 Homologous Body Structures
Some homologous body structures are vestigial and have no useful function even though they are still present, like hipbones in whales and boa constrictors, or a tail and cecum (appendix) in humans. Vestigial structures such as pelvic bones in the baleen whale are evidence of evolution.

30 Why Grow a Tail; or Legs…
The human embryo has a tail at 4 weeks; which disappears at about 8 weeks. Skinks are a type of lizard. In some species, legs have become so small they no longer function in walking. One explanation: The gene code is present to make the organ, but the function has been lost through change over time. If the organ is not vital to survival, then natural selection would not cause its elimination.

31 Similarities in Embryology
Embryos of many animals with back-bones are very similar.

32 It is clear that the same groups of undifferentiated cells develop in the same order to produce the same tissues and organs of all vertebrates, suggesting that they all evolved from a common ancestor.

33 Similarities in DNA Similarities in DNA and protein sequences suggest relatedness.

34 Similarities in Karyotypes
Similar karyotypes suggest an evolutionary relationship. Human- 46 chromosomes Chimpanzee- 48 chromosomes

35 Visual Evolution Peppered Moth
There is a natural variation in populations of peppered moths. Typica form – lighter Carbonaria form - darker

36 Peppered Moth The light colored form was the predominant form in England prior to the Industrial Revolution. Around the middle of the 19th century the darker form began to appear. It was first reported in By % of the moths in Manchester were the dark variety. In recent years, the burning of cleaner fuels and Clean Air regulations has reduced the pollution there and the lighter colored moths have increased in numbers.

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