Evolution Test Study Guide
Scientists estimate that the Earth is 4.6 billion years old. This gives time for evolution to occur, organisms to
adapt, and species to become extinct.
Charles Darwin was an English naturalist who traveled around the
world in the 1800’s. In the Galapagos Islands, he studied the variations
between the beaks of Galapagos finches. He noticed that while the
finches all had similarities and seemed to come from a common
ancestor, they each had different beaks, specialized for eating different
food sources. Darwin wrote a book called On the Origin of the Species,
which explained his Theory of Evolution through Natural Selection.
Evolution is the gradual change in populations over long periods of time. For there to be change in a
population over time it must start with a mutation which is a random change in DNA.
Species is defined as a group of organisms whose members can successfully reproduce. Populations are the
individuals of one species that live together in a given area.
Genetic variations (differences) result from mutations (changes) in the DNA.
colors and skin colors are examples of genetic variations.
Different hair colors, eye
Natural selection is the process by which organisms with favorable traits survive and reproduce at higher rates
than organisms without the trait. Natural selection happens continuously throughout time.
4 Parts to Darwin’s Theory of Evolution by Natural Selection
1. Overproduction: each species produces more offspring than will survive.
2. Genetic Variation: Individuals in a population are slightly different from
one another. These variations increase, decrease or have no effect on an
organism’s chance of survival. Differences in physical appearance are
caused by mutations, changes in DNA.
3. Struggle to survive: predators, disease, and the availability of resources
will limit the number of organisms that can survive to adulthood. Organisms
must compete for survival.
4. Successful Reproduction: is the key to natural selection. Individuals that
are well-suited to their environment will survive and reproduce, passing
down those successful traits to their offspring. The organisms that are not
well-suited or well-adapted are more likely to die early and not have
offspring.
Adaptation: A characteristic that helps an organism survive in its environment. Adaptations can include
structures and behaviors for finding food, for protection, and for moving from place to place.
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Examples:
o Structural - The smoky jungle frog’s color allows it to blend into the forest floor (camouflage)
o Structural - Humans now have the opposable thumb to grasp things.
o Behavioral – opossums platy dead to avoid being eaten by predators.
Many insects can adapt very quickly to pesticides because their generation time is short.
o They develop a genetic resistance to the pesticide.
o Resistance means that it does not affect or hurt them. This makes some insect populations (and
diseases) more difficult to control.
Organisms may become extinct if their environment changes and they cannot adapt quickly enough to
survive.
EVIDENCE OF EVOLUTION
1. Fossils: The solid remains or imprints of once-living organisms. Fossils are
commonly found in sedimentary rock. Fossils provide a historical sequence of life
known as the fossil record. Fossils found deeper in the Earth’s crust are usually
older than those found in the upper crust.
2. Vestigial Structures: Structures that were once useful in an ancestor,
but no longer useful. Ex: Whales having hind limb bones suggest that
whales have evolved from a land dwelling mammal.
3. DNA: Probably the most accurate piece of evidence to support the
theory of evolution. All organisms have DNA suggests we all came
from a common ancestor. The more closely related organisms are,
the more similar their DNA.
4. Homologous Structures:
Different organisms sometimes have
similar structures, such as bones, that may or may not be used in the
same way. This could suggest they came from a common ancestor.
5. Embryonic Structures: The more similar organisms look in early
stages of development, the more likely it is that they are closely
related.