11.3 Evidence of Evolution

11.3 Evidence of Evolution

  • Gene flow occurs when an individual travels from one location to another and joins a different population.
    • The brown allele is introduced into the green population.
  • There is compelling evidence for evolution.
    • The signature of past and present evolution is seen by biologists when looking at every level of organization.
  • Fossils show a progression of evolution and show that organisms from the past are not the same as those found today.
    • Scientists determine the age of fossils and categorize them all over the world to find out when the organisms lived relative to each other.
    • The fossil record shows the evolution of form over millions of years.
    • Sequences of species in the evolution of whales and modern horses have been recovered from highly detailed fossil records.
    • Horses in North America have a rich fossil record and many contain transition fossils.
    • The fossils show how the landscape changed from a forested one to a prairie as a result of a gradual drying trend.
  • The fossils of the horse and its ancestors are the basis of the artist's rendering.
    • The species depicted have many branches, dead ends, and adaptive radiations.
    • The evolution of a drying climate and increase in prairie versus forest habitat is one of the trends depicted here.
    • Przewalski's horse is a living horse.
  • The presence of structures in organisms that share the same basic form is a type of evidence for evolution.
    • The bones of different species have different shapes and sizes, but they have the same layout, evidence of descent from a common ancestor.
    • These parts are called homologous structures by scientists.
    • Some structures in organisms have no apparent function at all, and may be remnants of a past ancestor.
    • Some snakes have bones even though they don't have legs.
    • The sightless eyes of cave animals are one of the examples of vestigial structures.
  • The construction of these appendages suggests that these organisms are related.
  • To see examples of all kinds of evolutionary adaptation that illustrate the concepts of homologous and analogous bone structures, click through the activities at this guess.
  • The convergence of form in organisms that share the same environment is an example of evolution.
    • The ptarmigan, a bird, and the arctic fox, an unrelated animal, have temporary white coverings during the winter to blend with the snow and ice.
    • The benefits of not being seen by predators are what leads to the similarity.
  • The white winter coat of the ptarmigan is adapted to their environments.
    • By the time the adult or juvenile form is reached, structures that are absent in some groups often appear in their embryonic forms.
    • At some point in the embryo's early development, there are gill slits.
    • These disappear in the adult form of aquatic groups such as fish and some Amphibians.
    • The tail structure of great ape embryos is lost by the time of birth.
    • Even though the embryo of unrelated species are often similar, there can be differences in the adult that can be amplified by the changes in the embryo.
  • The distribution of organisms on the planet is best explained by evolution and the movement of tectonic plates.
    • The groups that evolved before the break up of the supercontinent Pangaea are distributed around the world.
    • The flora and fauna of the northern and southern regions of the planet are different.
    • The presence of Proteaceae in Australia, southern Africa, and South America is explained by the plant family's presence there prior to that.