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Darwin's Theories

Darwin's Hypothesis


     Darwin's hypothesis had three main parts to it:

  • Struggle for Existence
  • Survival of the Fittest
  • Descent With Modification

     ~Struggle for Existence

     Darwin thought back on Malthus' conclusion and realized that animals would have to compete to get necessities to live like shelter, food, territory, etc. Natural Selection comes to play in this too; some individuals in a species can get these necessities easier, faster, and better. The animals that can this live faster.

     ~Survival of the Fit

     Darwin defined fitness when an individual could survive in his environment and then produce offspring. He also believed that fitness is the result of adaptations. An adaptation is any trait that helps the individual survive. Survival of the Fit is mainly when an individual in a certain species is better suited for that environment. This can also be natural selection because the ones who are better suited for the environment will be able to produce offspring and they will carry on some of those traits that make them fit.

     ~Descent with Modification

     Descent with Modification is basically stating that living organisms today have come from other organisms and they may not look anything alike. This implies that all organisms are related to one another. Darwin believed that as animals adapted to new habitats they began to change differently.

Evidence of Evolution
     There are four main pieces of evidence that support Darwin's theory:
  • Fossil Record-

The fossil record shows how old the earth really to be. The fossils showed a gradual change over time. They showed that some organisms had lived for awhile and died out, too. It also proved what else he believed true that by looking at fossils you can see a change over time in that organism.

  • Geographic Distribution of Living Species-

Darwin's natural selection and descent with modification supported this. That through natural selection some organisms were "selected" over others because it could survive and flourish there. Descent with modification is also shown because organisms might have had different ancestors. But, they since some organisms live under the same environment "pressures" they have similar features.

  • Homologous Body Structure-

In a homologous body structure is when organisms have different ways of using certain mature structures but they are basically the same structure. An example of this is bones. Fish, mammals, and birds all have different mature forms. (Fish has fins; mammals have hoof, paw, or hand; and birds have wings.) But they still all have the "same" 5 groups of bones. This is probably one of the strongest evidence it suggests we (above animals) have all came from common ancestors.

  • Similarities in Early Development-

Like the above homologous this shows again that almost all animals have a similar ancestor. Organisms' embryos look very much alike and seem not to differ even if one is a bird, mammal, or reptile. 


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