Download Evolution Study Guide Darwin`s Theory of Natural Selection is the

Evolution Study Guide
Darwin’s Theory of Natural Selection is the accepted theory of how species evolve (change over time.) It states that
organisms best suited to their environment will survive and reproduce in greater numbers. They will pass their genes on to
their offspring, and future generations will look more like them.
Darwin identified 4 Principles of Evolution:
1. Overproduction: organisms have more offspring than will survive
2. Variation: within a species, there are variations of each trait,
3. Adaptation: some of those variations give some members of the species a survival advantage.
4. Selection: those members best suited to their environment will survive and reproduce in greater numbers.
Scientists have also learned that isolation of a populations of a species leads to speciation (the development of new species).
Examples are cichlid fish in Africa, squirrels in the Grand Canyon.
Genetic Variation within a species is necessary for that species to evolve. If there is little variation, members of a species will
not be able to survive changes in the environment. A major disadvantage of inbreeding is that it reduces the genetic variation
of a population.
Mutations are errors in DNA that occur during cell division. Mutations are a source of variation, but are not one of the
“principles of evolution”. Most mutations do not affect an organism. Some mutations are beneficial and may become an
adaptation (advantage) to organisms that have that mutation.
Human beings frequently make drastic, immediate changes to the environment through pollution, deforestation, building
dams, introducing invasive species, etc. Organisms have difficulty evolving to these changes because they are so fast. Species
with great genetic variation and short reproduction/maturation times are most able to adapt to these fast changes.
Many species have adapted to have some form of camouflage in their environment.
Biological Evidence for evolution:
 Homologous structures: organisms with similar structures (that have different functions) because they have a common
ancestor. This is a result of divergent evolution.
 Analogous structures: organisms that have different structures, with similar functions because they evolved in the same
environment. This is a result of convergent evolution.
 Vestigial Structures: left over or useless structures. An organism does not use this structure, but it is evidence of a
common ancestor with other organisms. Example: leg bones in snakes, leg bones in whales, wings of ostriches
 Similar Embryo development: early development of different species is similar
 Molecular/DNA similarities: organisms with common ancestors have similar chemical processes and proteins
(photosynthesis, hemoglobin) and a large percentage of similar DNA sequences.
Fossil Evidence of Evolution
Most organisms on earth die and do not form a fossil. Fossils found in rock layers provided evidence of the evolution of life on
earth. When comparing rock layers, the oldest fossils will be deeper than the youngest fossils, which are located closer to the
surface. Rock layers in different areas that have the same fossils are assumed to be the same age.
Living organisms are categorized by their structural and genetic similarities.
This is called taxonomy. The largest classification category is kingdom: animals, plants, fungus, protists, archaea and bacteria.
Within a kingdom there are further levels of classification (phylum, order, species...etc). Closely related organisms will have
more of these levels of classification in common than more distantly related organisms.
Evolution Study Guide
Darwin’s Theory of Natural Selection is the accepted theory of how species evolve (change over time.) It states that
organisms best suited to their environment will survive and reproduce in greater numbers. They will pass their genes on to
their offspring, and future generations will look more like them.
Darwin identified 4 Principles of Evolution:
5. Overproduction: organisms have more offspring than will survive
6. Variation: within a species, there are variations of each trait.
7. Adaptation: some of those variations give some members of the species a survival advantage.
8. Selection: those members best suited to their environment will survive and reproduce in greater numbers.
Scientists have also learned that isolation of a populations of a species leads to speciation (the development of new species).
Examples are cichlid fish in Africa, squirrels in the Grand Canyon.
Genetic Variation within a species is necessary for that species to evolve. If there is little variation, members of a species will
not be able to survive changes in the environment. A major disadvantage of inbreeding is that it reduces the genetic variation
of a population.
Mutations are errors in DNA that occur during cell division. Mutations are a source of variation, but are not one of the
“principles of evolution”. Most mutations do not affect an organism. Some mutations are beneficial and may become an
adaptation (advantage) to organisms that have that mutation.
Human beings frequently make drastic, immediate changes to the environment through pollution, deforestation, building
dams, introducing invasive species, etc. Organisms have difficulty evolving to these changes because they are so fast. Species
with great genetic variation and short reproduction/maturation times are most able to adapt to these fast changes.
Many species have adapted to have some form of camouflage in their environment.
Biological Evidence for evolution:
 Homologous structures: organisms with similar structures (that have different functions) because they have a common
ancestor. This is a result of divergent evolution.
 Analogous structures: organisms that have different structures, with similar functions because they evolved in the same
environment. This is a result of convergent evolution.
 Vestigial Structures: left over or useless structures. An organism does not use this structure, but it is evidence of a
common ancestor with other organisms. Example: leg bones in snakes, leg bones in whales, wings of ostriches
 Similar Embryo development: early development of different species is similar
 Molecular/DNA similarities: organisms with common ancestors have similar chemical processes and proteins
(photosynthesis, hemoglobin) and a large percentage of similar DNA sequences.
Fossil Evidence of Evolution
Most organisms on earth die and do not form a fossil. Fossils found in rock layers provided evidence of the evolution of life on
earth. When comparing rock layers, the oldest fossils will be deeper than the youngest fossils, which are located closer to the
surface. Rock layers in different areas that have the same fossils are assumed to be the same age.
Living organisms are categorized by their structural and genetic similarities.
This is called taxonomy. The largest classification category is kingdom: animals, plants, fungus, protists, archaea and bacteria.
Within a kingdom there are further levels of classification (phylum, order, species...etc). Closely related organisms will have
more of these levels of classification in common than more distantly related organisms.