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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.
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