The Theory of Evolution by Natural Selection

In science, theories are statements or models that have been tested and confirmed many times.

Theories have some important properties:

  • They explain a wide variety of data and observations
  • They can be used to make predictions
  • They are not absolute, they serve as a model of understanding the world and can be changed as the world view changes

In science, the term “Theory” does not express doubt.

In science, the term theory is used to represent ideas and explanations that have been confirmed through tests and observations

The theory of evolution remains one of the most useful theories in biology because it explains many questions and observations.

Some questions that can be answered by evolution.

  • 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 do organisms have structures they no longer use, like the appendix in a human? Non functioning wings in penguins
  • Why are there bones and fossil evidence of creatures that no longer exist? What happened to these creatures?
  • Why do so many organisms’ morphology and anatomy follow the same plan?
  • 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?
The Theory of Evolution is considered a Unifying Theory of Biology, because it answers many of these questions and offers and explanation for the data.
Darwin’s Theory of Evolution by Natural Selection

Darwin was a naturalist who observed many species. He is famous for his trips to the Galapagos Islands, his observations of the finches (and other animals) and the book he wrote: “The Origin of Species:

1. Variation exists among individuals in a species.
2. Individuals of species will compete for resources (food and space)
3. Differential survival and reproduction
4. Adaptation – increase in frequency of traits within the population that help individuals survive

Evidence of Evolution

1. Fossil Evidence

  • If today’s species came from ancient species, the we should be able to find remains of those species that no longer exist.
  • We have tons of fossils of creatures that no longer exist but bear striking resemblance to creatures that do exist today.
  • Carbon dating–gives an age of a sample based on the amount of radioactive carbon is in a sample.
  • Fossil record-–creates a geologic time scale.

2. Evidence from Living Organism

  • Fossil Evidence showing transitional species
  • Homologous Structures–structures that are embryologically similar, but have different functions, the wing of a bird and the forearm of a human
  • Vestigial Organs–seemingly functionless parts, snakes have tiny pelvic and limb bones, humans have a tail bone
  • Biochemistry and DNA
  • Embryological development–Embryos of different species develop almost identically
  • Observation of species change (wolves/dogs, peppered moths)

Examples of Evolution

1. industrial melanism (Kettlewell’s moths)
2. dog breeds
3. viruses & vaccines
4. bacteria & antibiotics
5. elephant tusks
6. stickleback fish
7. rock pocket mice