Download Study/Resource Guide for Evolution

Science
Unit 6: Evidence of Evolution
In this unit, you will study the evolution of organisms. You will explain the process
of natural selection by which the physical characteristics of organisms change over
successive generations. You will trace changes in life forms through the fossil record
and recognize that fossils provide evidence for a long history of change.
KEY TERMS
Inherited characteristics are the physical characteristics of an organism inherited from
its parents. The color of your eyes is an inherited characteristic, also called a trait. The
differences that are possible in a specific trait, such as eye color, are referred to as
variation. The genes you inherit will determine your physical characteristics such as eye
and hair color. Other characteristics, such as height and weight, might be affected by
your genes but will not be completely determined by genes. (S7L5a)
Evolution is the modification of a species over successive generations. Evolution
can also refer to the development of several species from one common ancestor
species. Whales are a good example of evolution. Whales are mammals with some
hair and lungs, but they live in aquatic environments like fish. Fossils of the earliest
whales strongly resemble the fossils of a group of scavenging carnivorous land-based
mammals. The most notable difference in the fossils are that the teeth of the whales
look very much like the teeth of fossils from later generations of whales and not like the
teeth of the mammals. Later whale fossils, roughly 20 million years younger than the
earliest whales, have large hands and feet with webbing. The toes are hooved much like
the older land-based mammals. Whale fossils from a few million years after that show
modifications of the hand and feet into flippers. (S7L5a, b, c)
The fossil record shows the point where a species changed enough to be considered
a different species but still shared the majority of its traits with a common ancestor.
The whale fossil record, for example, also shows a clear change in the species over
successive generations. One of the biggest challenges in following clear paths of
evolution for a species is finding fossils of successive generations of a species. It is not
always apparent when there are changes in a species. (S7L5c)
Natural selection is the process whereby nature selects which members of a species
survives based on certain traits. Suppose there is a population of mice that live in
a field that is full of tan-colored dry grass. There are black mice and tan mice. The
predators in the area can see the black mice easier and eat more of the black mice
because they are easier to locate. Over time, the mice that carry the genes for a tan
coat survive more often than the mice with black coats. This increases the population
of tan mice and increases the likelihood that the majority of future generations will be
tan. (S7L5b)
Important Tip
It is important to understand that evolution does not necessarily result in
“improvement” or greater complexity of organisms. Many fossil findings demonstrate
that life does not always steadily evolve from simple to complex. For example,
fossils in the Burgess Shale site in the Canadian Rocky Mountains have revealed
that quite complex organisms existed more than 540 million years ago. Examples of
most major groups of modern animals were discovered in this fossil deposit. (SL5b)
Georgia Milestones Grade 7 EOG Study/Resource Guide for Students and Parents
Copyright © 2015 by Georgia Department of Education. All rights reserved.
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Science
Sample Items 20–24
Item 20
Which of the following BEST describes the effect that natural selection might have
on a species over time?
A. The fur color of a species will always change over time, because of natural
selection.
B. Predator species will always increase due to natural selection, while prey species
will always die out.
C. Members of a species with traits that allow them to survive and reproduce in an
environment will increase in population, while those without those traits will die.
D. Bigger members of a species always have an advantage over smaller members.
Therefore, over time, a species will eventually include larger organisms only.
Item 21
The walking catfish is a species of fish that walks on land using its pectoral fins.
During drought conditions, when there is little water in its habitat, the walking
catfish can use its pectoral fins to get to areas with water.
Which of these will MOST LIKELY happen to a population of walking catfish over
time if all nearby aquatic environments dry up permanently?
A. Walking catfish with small pectoral fins are more likely to survive a trip to distant
areas of water. The population is likely to evolve to have smaller pectoral fins.
B. Walking catfish with large pectoral fins are more likely to survive a trip to distant
areas of water. The population is likely to evolve to have larger pectoral fins.
C. Walking catfish with large pectoral fins and those with small pectoral fins are
equally likely to survive a trip to distant areas of water. Both types survive, so
evolution is unlikely to occur.
D. Walking catfish with large pectoral fins and those with small pectoral fins are
equally likely to not survive the trip to distant areas of water. Both types of catfish
will then become extinct.
Page 146 of 208
Georgia Milestones Grade 7 EOG Study/Resource Guide for Students and Parents
Copyright © 2015 by Georgia Department of Education. All rights reserved.
Science
Item 22
Scientists find fish fossils in Rock Layers B and C of a canyon. The fossil found in
Rock Layer B is similar to the fossil found in Rock Layer C.
Fossils Found in Rock Layers
Rock Layer C
Rock Layer B
Rock Layer A
Which conclusion is BEST supported by the order of the layers?
A.
B.
C.
D.
The two fossils are different species, because they are in adjacent layers.
The two fossils are the same species, because they are in adjacent layers.
The species in Layer C may have evolved from the species in Layer B.
The species in Layer B may have evolved from the species in Layer C.
Item 23
A science class takes a field trip to a rock formation known for the many fossils it
holds. A student finds a fossil that shows a plant with leaves similar to those of a
plant that grows nearby. The student tells his classmates that the plants must be
an ancient species that has not changed much over time.
Which statement BEST describes the student’s claim?
A.
B.
C.
D.
The claim is reasonable because plants do not change over time.
The claim is reasonable because fossils are records of things that lived long ago.
The claim is not reasonable because plants must change over time.
The claim is not reasonable because fossils can be made from recently living
organisms.
Georgia Milestones Grade 7 EOG Study/Resource Guide for Students and Parents
Copyright © 2015 by Georgia Department of Education. All rights reserved.
Page 147 of 208
Science
Item 24
Fire ants in the southeastern United States were accidentally introduced over
seventy years ago. Stings from fire ants can be deadly to the native fence lizard.
Fence lizards that have lived in areas with fire ants for many generations have
longer legs than fence lizards that have not lived in areas with fire ants until
more recently.
Which statement BEST describes how the legs of the fence lizard changed
over time?
A. Over time, fence lizards with longer legs were more likely to survive and passed this
trait on to offspring.
B. Over time, fence lizards stretched their legs to increase leg length and passed this
trait on to their offspring.
C. The lizards of each generation are born without longer legs. They then grow the
longer legs to avoid stepping on the fire ants.
D. The lizards living in areas where fire ants were first introduced used the venom
from fire ants to grow longer legs. The trait for longer legs was then passed on to
offspring.
Page 148 of 208
Georgia Milestones Grade 7 EOG Study/Resource Guide for Students and Parents
Copyright © 2015 by Georgia Department of Education. All rights reserved.