nothing in biology makes sense except in the light of evolution theodosius dobzhansky 1900 1975 n.
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Photo by “davemee” flickr creative commons. "nothing in biology makes sense except in the light of evolution” ~Theodosius Dobzhansky (1900-1975). Statements or models that have been tested and confirmed many times. In science, the term "Theory" does not express doubt.

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nothing in biology makes sense except in the light of evolution theodosius dobzhansky 1900 1975

Photo by “davemee” flickr creative commons

"nothing in biology makes sense except in the light of evolution”

~Theodosius Dobzhansky (1900-1975)


In science, the term "Theory" does not express doubt.

    • Explain a wide variety of data & observations
    • Can be used to make predictions
    • Are not absolute, can be changed as new evidence is found

Why do so many different animals have the same structures, the arm bones in a human are the same bones as a flipper in a whale?

  • Why is the sequence of DNA very similar in some groups of organisms but not in others?
  • Why do the embryos of animals look very similar at an early stage?

Charles Darwin

  • explained how organisms changed over time  (ADAPTED)

Lamarke's Theory of Acquired Characteristics

    • Thought that you would gain or lose features if you overused or didn't use them
  • Proven to be wrong!

Photo courtesy of ucumari, creative commons, flickr


Darwin was a naturalist (what we today call biologists)

  • He traveled the world and made observations and sketches of many species
  • His most famous travels were aboard the H.M.S. Beagle where he traveled to the Galapagos Islands

Marine Iguana, photo courtesy of mtchm, flickr creative commons

Blue-footed booby, photo courtesy of stirwise, flickr creative commons


Finch, photo courtesy of stirwise, flickr, creative commons

Giant tortoise, photo courtesy of Planetgordon, flickr creative commons


Darwin noted that there existed many finches on the islands, but while they had similarities, each was adapted to eating a particular type of island food

  • He concluded that the finches all came from one ancestral species and evolved into many new species

Cactus finch, photo courtesy of zrim, flickr creative commons


Darwin published this work to explain the variety of species that exist on the planet

  • He proposed the “Theory of Evolution by Natural Selection”

1. Variation exists among individuals in a species.2. Individuals will compete for resources (food, mates, and space)3. Competition would lead to the death of some individuals while others would survive4. Individuals that had advantageous variations are more likely to survive and reproduce.

This process came to be known as Natural SelectionThe favorable variations are called Adaptations

Photo courtesy of digitalART2, flickr creative commons


Say in a species of blob….there exists blobs of all shapes and sizes (variation)

Blobs eat the little purple organisms that live underground and on the surface.


During a particularly hot year, food became less abundant (competition), blobs that had the ability to dig into the soil to get food had a better chance of survival.

Many blobs died that year…….


The next generation had move blobs with the pointed noses. That is NATURAL SELECTION.

  • Variation
  • Competition
  • Survival
  • Reproduction

Fossil Evidence

    • Shows numbers extinct animals
    • Shows similarities between extinct animals and animals that are alive today
    • The earth’s layers show a time scale of species and when they appeared on earth (and when they died out)

Dinosaurs have always fascinated us, movies such as Jurassic Park capitalize on that fascination.

How do we know what dinosaurs looked like?

We create a picture based on the bones we find (fossils) and use modern reptiles to guess at their texture and skin color.


Homologous structures – these are parts of the body that are similar, but have different functions

ex. The flippers of whales, and the wings of birds

All forelimbs of vertebrates have the same pattern of bones

• Common ancestry


Vestigial Organs – these are organs or parts that seem to have no function

Whales have pelvic bones that do not attach to legs


Biochemistry and DNA

  • When comparing the DNA of one species to another, more similarities are found in species that are more closely related.

Lion photo credit: ucumari Tiger photo credit: digitalART2


Embryological Development

Embryos of different species develop in almost identical ways.

Human fetus at 8 weeks


Direct observation of species change

    • Bacteria become resistant to antibiotics
    • Wolves were bred over many generations to become dogs (artificial selection) • and then bred further to create a variety of breeds