Chapter 6 Evolution
Vocabulary:
Section 1:
Adaptation: any variation that makes an organism better suited to its environment
Evolution: changes in inherited characteristics of a species over time
Gradualism: describes evolution as a slow, ongoing process
Natural selection: organisms with traits best suited to their environment will more likely
survive and reproduce
Punctuated Equilibrium: model that says gene mutation can result in a new species in
a relatively short time.
Species: group of organisms that share similar characteristics and can reproduce among
themselves to produce fertile offspring
Variation: an inherited trait that makes an individual different from other members of its
species; an adaptation is a variation that makes an organism better suited to its
environment.
Section 2:
embryology (em bree AH luh jee): the study of embryos and their development
homologous (hoh MAH luh gus): body parts that are similar in origin and structure
sedimentary rock: rock in which most fossils are found, formed when layers of sand, silt, clay,
or mud are pressed and cemented together, or when minerals are deposited from a solution
vestigial (veh STIH jee ul) structures: structures that do not seem to have a function
radioactive element: an element that gives off a steady amount of radiation as it slowly changes
to a nonradioactive element
mutation: permanent change in organisms DNA
fossils: found in sedimentary rock show evidence that living things evolved.
Section 3:
hominids: humanlike primates that lived about 4 million to 6 million years ago and were
different from the other primates
Homo sapiens: direct ancestors of hominids
primates: group of mammals with opposable thumbs, binocular vision, and flexible
shoulders
Section 6-1….Mechanism of Evolution:
Early thought about Evolution:
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Species have changes over time = physical characteristics have changed
Jean Baptiste Lemark believed that species evolve by keeping traits their parents
gained during their lives. Ex. Lose an ear and your children will have one less
ear.
Lamarck’s theory of acquired characteristics was not supported by evidence.
Evolution by Natural Selection:
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Charles Darwin was a naturalist that sailed to South America to study the
Galapagos Islands in South America on a Ship called the Beagle in 1831.
Darwins Theory of Natural Selection canceled Lemarks Theory of Acquired
Characterstics.
Darwin wrote a book “On the Origin of Species by Means of Natural
Selection.”(published 1859)
Darwin’s Rules That support Natural selection:
1. Organism reproduce more offspring so they can survive
2. Variations are found in individuals of a species
3. Some variations are better suited to reproduce and survive
4. Over time better adapted individuals that make up a species and make the
species more stable.
Adaptation and Variation:
 Variations in a species can be helpful or harmful
 New species can arise from existing species if the variation is large
enough.
 Examples of adaptation can be coat color, shape (height), chemical
make up.
 If an adaptation is not advantageous for the survival of the
organism it will die
2 models explain the speed of evolution.
1. Gradualism:
 Darwin stated that the evolutionary process was slow and steady
 Current organisms came from previous ancestors and there were intermediate
forms = gradualism
2. Punctuated Equilibrium:
 A new species arise due to mutation and favorable environmental conditions =
rapid evolution = the opposite of GRADUALISM
Section 6-2 Evidence of Evolution:
A. Fossils found in sedimentary rock show evidence that living things evolved.
B. Fossil age can be determined by 2 basic methods.
1. Relative dating looks at fossil location in a particular layer of rock; older rock layers
are under newer rock layers.
2. Radiometric dating compares the amount of radioactive element with the amount of
nonradioactive element in a rock.
C. 4 Reasons fossil records have gaps.
1. Incomplete rock record; most organisms do not become fossils.
2. Enough fossils have been discovered for scientists to conclude that complex organisms
appeared after simpler ones.
3. Most organisms that have ever existed are now extinct.
Direct evidence, such as the development of antibiotic resistance in bacteria, supports
evolution.
4 ways in which indirect evidence supports evolution
1. Embryology - the study of embryos and their development, shows similarities among
all vertebrate species.
2. Homologous - body parts can indicate two or more species share common ancestors.
3. Vestigial structures - structures that don’t seem to have a function but might have
once functioned in an ancestor
4. DNA can provide evidence about how closely related organisms are.
Section 3: The Evolution of Primates
A. Primates—group of mammals with opposable thumbs, binocular vision, and flexible
shoulders
1. Hominids appeared about 4 to 6 million years ago and had larger brains than apes.
2. Fossils, such as Australopithecus, point to Africa as the origin of hominids.
3. Homo habilis and Homo erectus are thought to be early human ancestors.
B. Homo sapiens began evolving about 400,000 years ago.
1. Neanderthals had short, heavy bodies with thick bones, small chins, and heavy brow
ridges.
a. Disappeared about 30,000 years ago
b. Not thought to be direct ancestors of modern humans (different genetic makeup than
Homo sapiens, chromosomes are not similar)
2. Cro-Magnon fossils date from around 10,000 to 40,000 years ago; Cro-Magnon
humans are thought to be direct ancestors of early Homo sapiens.
Sexual reproduction and mutation can increase
the variation of a species. These new traits
can allow the organism to adapt to new
environments. This increased adaptation can
cause the organism to evolve.