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. Camouflage is an example of
an adaptation.
4. Selection: those members best suited to their environment will survive and reproduce in greater numbers. Selective
Pressures are environmental factors which may reduce reproductive success in a population and thus contribute to
evolutionary change or extinction through the process of natural selection. Examples of selective pressures are: predation,
disease, climate change, pollutants, loss of habitat
Scientists have also learned that isolation of populations within a species leads to speciation (the development of new
species). Examples are cichlid fish in Africa, squirrels on opposite rims of 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. One of the major disadvantage of inbreeding is that it reduces the genetic
variation of a population. Species with great genetic variation and short reproduction/maturation times are most able to adapt
to environmental changes.
Mutations are errors in DNA copies that occur during cell division. Mutations are the 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.
Biological Evidence of evolution:
 Homologous structures: organisms with similar structures that have different functions because they have a common
ancestor. This is a result of divergent evolution. Organisms evolved in different environments, so the function of the
structure is different (fins vs wings vs legs)
 Analogous structures: organisms that have different structures, with similar functions because they evolved in the same
environment. This is a result of convergent evolution. This is a result of different species evolving in similar environments
with similar selective pressures. (butterfly wings vs bat wings)
 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. Vestigial
structures are used as homologous structures.
 Similar Embryo development: early development of different species is similar. The greater the length of time two
different species embryos resemble each other, the more closely they are related through evolution.
 Molecular/DNA similarities: organisms with common ancestors have similar chemical processes and proteins
(photosynthesis, hemoglobin) and a large percentage of similar DNA sequences within a specific gene.
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
eubacteria. 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. This taxonomy is also
depicted in phylogenetic trees.
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. Camouflage is an example of
an adaptation.
8. Selection: those members best suited to their environment will survive and reproduce in greater numbers. Selective
Pressures are environmental factors which may reduce reproductive success in a population and thus contribute to
evolutionary change or extinction through the process of natural selection. Examples of selective pressures are: predation,
disease, climate change, pollutants, loss of habitat
Scientists have also learned that isolation of populations within a species leads to speciation (the development of new
species). Examples are cichlid fish in Africa, squirrels on opposite rims of 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. One of the major disadvantage of inbreeding is that it reduces the genetic
variation of a population. Species with great genetic variation and short reproduction/maturation times are most able to adapt
to environmental changes.
Mutations are errors in DNA copies that occur during cell division. Mutations are the 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.
Biological Evidence of evolution:
 Homologous structures: organisms with similar structures that have different functions because they have a common
ancestor. This is a result of divergent evolution. Organisms evolved in different environments, so the function of the
structure is different (fins vs wings vs legs)
 Analogous structures: organisms that have different structures, with similar functions because they evolved in the same
environment. This is a result of convergent evolution. This is a result of different species evolving in similar environments
with similar selective pressures. (butterfly wings vs bat wings)
 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. Vestigial
structures are used as homologous structures.
 Similar Embryo development: early development of different species is similar. The greater the length of time two
different species embryos resemble each other, the more closely they are related through evolution.
 Molecular/DNA similarities: organisms with common ancestors have similar chemical processes and proteins
(photosynthesis, hemoglobin) and a large percentage of similar DNA sequences within a specific gene.
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
eubacteria. 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. This taxonomy is also
depicted in phylogenetic trees.