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GEOLOGY 12
CHAPTER 8
PATTERNS OF EVOLUTION
NOTES
EVIDENCE FOR EVOLUTION
INDIRECT
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fossils (many forms now extinct) •
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•
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changes in a single species of snail
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DIRECT
common ancestry (adaptive radiation)
similar (homologous) structures
vestigial organs (suggests common ancestry)
biochemistry (molecular unity; see Unit 2)
embryology (study of embryo development)
genetics (cellular unity, DNA materials)
GENETICS
Trees of Life
COMPARATIVE ANATOMY
HOMOLOGOUS VS ANALOGOUS STRUCTURES
aka
Analogous
Structures
NOTE: ANALOGOUS STRUCTURES
Analogous structures are products of CONVERGENT EVOLUTION. The structures serve
the same function, but have different origins. The pectoral fin of a shark and the flipper of
a whale are analogous. The wing of an insect and the wing of a bird are also analogous
structures.
COMPARATIVE ANATOMY
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Chapter 8 Notes
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TYPES OF EVOLUTION
KEY IDEA
The basic evolutionary mechanisms—mutation, migration, genetic drift, and natural
selection—can produce major evolutionary change if given enough time.
PUNCTUATED EQUILIBRIUM VS GRADUALISM
The "PUNCTUATED EQUILIBRIUM" theory was proposed as a criticism of the traditional
Darwinian theory of evolution. ELDREDGE and GOULD observed that evolution tends to
happen in FITS AND STARTS, sometimes moving very fast, sometimes moving very
slowly or not at all. On the other hand, typical variations tend to be small. Therefore,
DARWIN saw evolution as a SLOW, continuous process, without sudden jumps.
(GRADUALISM) However, if you study the FOSSILS of organisms found in geological
layers, you will see long intervals in which nothing changed ("equilibrium"), "punctuated"
by short, revolutionary transitions, in which species became extinct and replaced by
wholly new forms. Instead of a slow, continuous progression, the evolution of life on Earth
seems more like the life of a soldier or a fire fighter: long periods of boredom interrupted
by rare moments of terror.
MICROEVOLUTION VS MACROEVOLUTION
MICROEVOLUTION is evolution on a small scale—within a single population.
House sparrows have adapted to the climate of North America, mosquitoes have evolved
in response to global warming, and insects have evolved resistance to our pesticides.
These are all examples of microevolution—evolution on a small scale.
Macroevolution is evolution on a grand scale—what we see when we look at the overall
history of life: stability, change, lineages arising, and extinction.
MUTATION
CROSSING OVER during meiosis produces variety within a species but MUTATION is
the ultimate source of NEW genetic varieties in a species. GENE FLOW can also be
responsible for the introduction of NEW ALLELES into a population of a species but,
generally, the most rapid and dramatic evolution is due to NATURAL SELECTION.
A process like MUTATION might seem too small-scale to influence a pattern as amazing
as the number of different beetles, or as large as the difference between dogs and pine
trees, BUT IT’S NOT. Life on Earth has been accumulating mutations and passing them
through the filter of natural selection for 3.8 billion years — more than enough time for
evolutionary processes to produce its biodiversity history.
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Chapter 8 Notes
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KEY IDEA
DIVERGENT and CONVERGENT evolution and CO-EVOLUTION are different ways
organisms adapt to the environment. These are examples of how the diversity of life on
earth is due to the ever-changing interaction between a species and its environment.
CONVERGENT EVOLUTION
In the frigid waters of the ocean surrounding ANTARCTICA, fish have a special trait
which allows them to survive the big chill. As scientists discovered in the 1960s, the fish
have adapted by evolving a kind of ANTIFREEZE. It's composed of molecules called
GLYCOPROTEINS that circulate in the blood of the fishes, slightly lowering the
temperature at which their body fluids would otherwise freeze and kill them. The
glycoproteins surround tiny ice crystals and keep them from growing.
It's another of those ingenious evolutionary solutions that seem almost too clever to be
true. But consider this: Nature did it not once, but at least twice. Fish at the other end of
Earth, in the ARCTIC, also have ANTIFREEZE PROTEINS. But those two populations of
fish split long before they developed the antifreeze genes and proteins. And, researchers
have found, the genes that produce the antifreeze proteins, north and south, are quite
different. This is evidence that quite separate, independent episodes of molecular
evolution occurred, with the same functional results.
This is a dramatic example of CONVERGENT EVOLUTION, when organisms that aren't
closely related evolve similar traits as they both adapt to similar environments.
CONVERGENT EVOLUTION is also responsible for…
• the WINGS of the bat, the bird, and the pterodactyl. In each case, the forelimbs of
these vertebrates morphed over time into wings, but they did so INDEPENDENTLY.
• the different sorts of ANTEATERS found in Australia, Africa, and America. Though not
closely related, they all evolved the "tools" necessary to subsist on an ant diet: a long,
sticky tongue, few teeth, a rugged stomach, and large salivary glands. In each case,
evolutionary adaptations allow them to exploit a food niche of ants and termites, but
the developments occurred INDEPENDENTLY.
DIVERGENT EVOLUTION
The ADAPTIVE RADIATION of Darwin’s finches is one example of DIVERGENT
EVOLUTION. Divergent evolution is the process of two or more RELATED SPECIES
becoming more and more DISSIMILAR.
Some of Darwin’s finches
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Chapter 8 Notes
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The red fox and the kit fox provide another example of two species that have undergone
divergent evolution. The RED FOX lives in mixed farmlands and forests, where its red
color helps it blend in with surrounding trees. The KIT FOX lives on the plains and in the
deserts, where its sandy color helps conceal it from prey and predators. The ears of the
kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its
desert environment. The enlarged surface area of its ears helps the fox get rid of excess
body heat. SIMILARITIES IN STRUCTURE INDICATE that the red fox and the kit fox had
a COMMON ANCESTOR. As they adapted to different environments, the APPEARANCE
of the two species DIVERGED.
CO-EVOLUTION
Co-evolution is the joint change of two or more species in close interaction.
PREDATORS and their PREY sometimes co-evolve; PARASITES and their HOSTS
often co-evolve; plant-eating animals and the plants upon which they feed also co-evolve.
One example of co-evolution is between PLANTS and the ANIMALS that pollinate them.
In tropical regions BATS visit FLOWERS to eat nectar. The fur on the bat's face and neck
picks up pollen, which the bat transfers to the next flower it visits. Bats that feed at
flowers have a slender muzzle and a long tongue with a brushed tip. These adaptations
aid the bat in feeding. flowers that have coevolved with bats are light in color. Therefore,
bats, which are active at night, can easily locate them. The flowers also have a fruity odor
attractive to bats.
EXTINCTION
Over 99% of the species that HAVE EVER lived on Earth have gone EXTINCT! Present
day biodiversity is the result of an accumulation of changes due to extinction events over
millions of years.
EXTINCTION contains three important elements.
• For geographically WIDESPREAD species, extinction is rare.
• The largest MASS EXTINCTIONS produce major restructuring of the biosphere
wherein some successful groups are eliminated, allowing previously minor groups to
expand and diversify.
• It is generally impossible to predict which species will be VICTIMS of an extinction
event.
PHYLOGENETIC TREE
The Tree of Life represents the PHYLOGENY of
organisms (i.e. the history of organism lineages as
they change through time). It implies that different
species arise from previous forms and that all
organisms, from the smallest microbe to the largest
plants and vertebrates, are connected. In a
phylogenetic tree. Each NODE represents the most
recent common ancestor of the descendants, and
edge lengths correspond to time estimates.
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Chapter 8 Notes
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