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Evolution - PowerPoint PPT Presentation

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Evolution. Evolution. Change over time Process by which modern organisms have descended from ancient organisms. Charles Darwin. Born in England 1809 Set sail on H.M.S. Beagle in 1831 for voyage around the world

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  • Change over time

  • Process by which modern organisms have descended from ancient organisms

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Charles Darwin

  • Born in England 1809

  • Set sail on H.M.S. Beagle in 1831 for voyage around the world

    • Made numerous observations and collected evidence that led him to propose the theory of evolution – how life changes over time

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Darwin’s Observations

  • Observed a tremendous amount of diversity in plants and animals

  • 68 different beetle species in one day in a Brazilian forest

  • Plants and animals well suited to whatever environment they inhabited

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Darwin’s Observations

  • Intrigued by which organisms survived and produced offspring

  • Collected fossils that resembled organisms that were still alive

  • Most influenced by Galapagos Islands

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Galapagos Islands

  • Very different climates on each island

  • Paid particular attention to giant tortoises, marine iguanas, and finches

  • Organisms varied in predictable ways from one island to another

    • ie. Tortoise shells

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Galapagos Islands

  • Darwin proposed that animals living on different islands had once been members of the same species

  • Species would have evolved from an original South American ancestor species after becoming isolated from one another

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Galapagos Tortoises

Pinta IslandIntermediate shell

Hood Island

Saddle-backed shell

Isabela Island

Dome-shaped shell

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Darwin’s Influences

  • Society was not receptive to Darwin’s “radical” ideas

  • Certain scientists who preceded Darwin helped to shape his views

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Hutton’s Theory

  • Hutton’s Theory of Geological Change

  • James Hutton (1795) a geologist

    • Rocks, mountains, and valleys are shaped by a variety of natural forces

      • i.e. Rain, heat, & cold temperatures

    • Geological processes operate extremely slowly therefore Earth had to be much older than a few thousand years old

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Lyell’s Principles

  • Lyell’s Principles of Geology

  • Charles Lyell (1833) geologist

    • The Processes that changed Earth in the past are the same processes that operate in the present

    • Scientists recognize that Earth is many millions of years old

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Movement of Earth’s Crust

Sea level

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.

New sediment is then deposited above the exposed older rock surface.

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Lamarck’s Theory of Evolution

  • Jean Baptiste Lamarck French naturalist (1809)

  • proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime.

    • These traits could be passed on to their offspring.

    • Led to changes in species

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Tendency Toward Perfection

  • All organisms have a innate tendency toward perfection

    • Ancestors of birds acquired an urge to fly,

    • Birds kept trying to fly,

    • Their wings increased in size,

    • Birds are now suited to flying

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Use and Disuse

  • Organisms could alter the size or shape of particular organs by using their bodies in new ways

    • Birds try to use front limbs to fly, they grew wings

    • If a winged animal did not use its wings they would decrease in size and disappear

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Inheritance of Acquired Traits

  • Lamarck thought acquired characteristics could be inherited.

    • If you spent your life lifting weights to build muscles then your children would inherit big muscles, too.

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Evaluating Lamarck

  • Lamarck’s theory of evolution is incorrect because:

    • He did not know how traits are inherited.

    • Behavior has no effect on genetics

  • He was the first:

    • to develop a theory of evolution

    • First to realize that groups of organisms do adapt to their environment

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Population Growth

  • Thomas Malthus (1798) – English Economist

  • Observed that babies were being born faster than people were dying.

  • Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

    • Proposed that war, famine, and disease limit the growth of human populations.

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Darwin Presents His Case

  • Publication of On theOrigin of Species

    * Darwin’s discoveries went totally against the scientific ideas of the 1800’s

    * He did not publish his research until he read Alfred Russel Wallace’s essay, which summarized Darwin’s thoughts on evolution.

    * Published 25 years after his trip

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Natural variation and artificial selection

  • Darwin’s critics believed that all species were perfect and unchanging

  • Natural variation: differences among individuals of a species, found in all types of organisms.

    • Darwin proposed that much of the variation in populations can be inherited, or passed on to the next generation

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Artificial Selection

  • Darwin actually made some of his greatest progress studying English farmers and breeders

  • Artificial selection: nature provides variation among different organisms, humans select and breed for those variations that they find useful.

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Evolution by Natural Selection

* The struggle for existence

* Competition for resources

* Food, water, shelter, mates, etc.

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Survival of the Fittest

  • The better suited an organism is to its environment, the better chance it has at surviving

  • The ability of an individual to survive and reproduce in its specific environment – fitness

  • The inherited characteristics that increase an organism’s chance of survival - adaptation

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Descent With Modification

  • Over time, natural selection has produced species that are different than their ancestors

  • Looking backwards in time you should find the common ancestor of all living things – common descent

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Evidence of Evolution

Fossil Record

  • Darwin believed that life on Earth has been evolving for millions of years

    • Darwin saw the fossil record as a detailed record of life on Earth

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Evidence of Evolution

Geographic Distribution of Living Species

  • Darwin found that organisms living under similar ecological conditions end up evolving similarities without being related – Convergent Evolution

  • Ex – Fish and whales

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Evidence of Evolution

  • Homologous Body structures

    * The limbs of birds, reptiles, and mammals may have different looks but they form from the same embryonic tissue – Divergent Evolution

    * Similarities of Early Development

    * Animals have similar embryological development

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Homologous Structures





Typical primitive fish

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Summary of Darwin’s Theory

  • Variations are inherited

    2. In nature, tendency towards overpopulation

    3. Not all organisms survive – compete for resources

    4. Natural Selection – struggle for existence

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Summary of Darwin’s Theory

5. Individuals best suited to their environment survive and reproduce most successfully

6. Species change over time

7. Populations today come from modifications of species of the past

8. All organisms are united into a single tree of life by common decent