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Chapter 6 Review: Change over Time
1. Define the following terms.
Species - is a group of similar organisms that can mate with each other and produce fertile offspring
Adaptation - a trait that helps an individual survive and reproduce
Variation-any difference between individuals of the same species
Theory - a well-tested concept that explains a wide range of observations
Evolution - process by which populations accumulate inherited changes over time
Artificial Selection (Selective Breeding) – when humans use the steps of natural selection to select for
traits in animals, plants, etc. that benefit humans. This process is greatly speeded up when compared
with natural selection.
Mutation – a change in the DNA including adding, deleting or substituting a base pair
Homologous Structures – structures that are similar in different species & that have been inherited
from a common ancestor
Vestigial Structures - Remnants of once useful structures that no longer have a purpose
2. Describe how the following pieces of evidence support the theory of evolution.
Embryo development – embryos in similar groups, such as vertebrates, develop in the same
sequence which suggests a common ancestor
Fossil Record - Provides a historical sequence of life called the fossil record (ex. Fossils found in
the upper layers tend to resemble present day organisms, deeper layer fossils tend to look quite
different) This demonstrates that life has changed over time.
Body structure – comparing skeletal structure, embryo development one can observe the
relationship among groups of organisms
DNA - If organisms have evolved from a common ancestor, they must share much of their genetic
information which has shown to be the case
Each of the above evidences can alone provide proof of evolution.
True
Which of the above evidences is the strongest evidence of evolution? DNA
False
3. Describe the four steps of natural selection.
1. Overproduction: more offspring are produced than can be supported in the environment
2. Genetic variation: each individual has slight differences (strengths & weaknesses with respect
to the current environment)
3. Struggle to survive (competition): individuals will compete for the limited resources
4. Successful Reproduction (selection): those individuals who are well suited to the environment
are more likely to survive and reproduce passing on their successful adaptations.
4. Use the steps of natural selection, and the bell curve (normal distribution curve) below, to explain
how bacteria can become resistant to antibiotics.
Average
Weak
Strong
In a population of bacteria, some will be easily killed by antibiotics, some will be resistant to
antibiotics, and most will be average in their ability to resist antibiotics. When antibiotics are introduced
into the environment the weak will die first, the average next and the resistant last. Any bacteria that
happens to have a mutation that allows it to survive the medication will survive and reproduce. It’s
offspring will likely also have the resistant adaptation and our normal distribution will move toward
resistance becoming a normal or average trait.
5. How might natural selection affect a portion of a species that becomes isolated from the rest of its kind?
(example = A species of squirrel becomes stranded on an island as sea level rises)
Given enough time, the two species will experience selection from different pressures in their
environments. Over time, the species will begin to diverge. Different traits will be successful in
each environment. Eventually the two species will become so different they can no longer
interbreed = speciation.
6. Which animal spurred Darwin’s thinking about how species might change over time during his voyage on the
HMS Beagle? finch
7. Darwin observed the obvious variation that occurs within species, but he couldn’t explain what caused these
variations. We now know these variations come from each organism’s unique combination of genes along
with occasionally successful mutations in the genes.
8. Which of the following organisms can demonstrate changes resulting from evolution fastest?
a. Humans
b. bacteria
c. elephants d. mushrooms
Why? They produce offspring faster (shorter generation time). The more offspring the
more opportunity for new gene combinations and mutations, which can then be selected
for in a changing environment
9. Compare and contrast gradualism and punctuated equilibrium.
Gradualism: small changes that add up to major changes over a long period of time (slowly and
steadily) Punctuated Equilibrium: species evolve during short periods of rapid change (quickly
over short periods of time)
10. The amount of similarity between the DNA of two species allows scientists to gauge the time since the
organisms shared a common ancestor.
11. Circle the points on the evolutionary tree below that represents where each organism diverged from a
common ancestor.
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