Transcript chapter16_Sections 1

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 16
Evidence of Evolution
(Sections 16.1 - 16.5)
Albia Dugger • Miami Dade College
16.1 Reflections of a Distant Past
• Events of the ancient past can be explained by studying
physical, chemical, and biological processes
• An asteroid impact may have caused a mass extinction 65.5
million years ago
• mass extinction
• Simultaneous loss of many lineages from Earth
The K-T Boundary Layer
• A unique rock layer that formed
worldwide 65.5 million years ago
marks an abrupt transition in the
fossil record which implies a mass
extinction
16.2 Early Beliefs,
Confounding Discoveries
• Expeditions by 19th century naturalists such as Alfred
Wallace yielded increasingly detailed observations of nature
• Geology, biogeography, and comparative morphology of
organisms led to new ways of thinking about the natural world
Key Terms
• naturalist
• Person who observes life from a scientific perspective
• biogeography
• Study of patterns in the geographic distribution of species
and communities
• comparative morphology
• Study of body plans and structures among groups of
organisms
Biogeography
• Traveling naturalists noted unexplained patterns in the
geographic distribution of species
• Plants and animals living in extremely isolated places looked
similar to species living on different continents
• Example: Three similar ratite birds – the emu of Australia,
rhea of South America, and ostrich of Africa
Similar-Looking, Related Species
Similar-Looking, Related Species
A Emu, native to Australia
Fig. 16.2a, p. 238
Similar-Looking, Related Species
B Rhea, native to South America
Fig. 16.2c, p. 238
Similar-Looking, Related Species
C Ostrich, native to Africa
Fig. 16.2b, p. 238
Comparative Morphology
• Naturalists also had trouble classifying organisms that are
outwardly very similar, but quite different internally
• Example: the American spiny cactus and African spiny spurge
live in similar environments, but are native to different
continents – their reproductive parts are very different, so they
can’t be as closely related they appear
Similar-Looking, Unrelated Species
Comparative Morphology
• Other organisms that differ greatly in outward appearance
may be very similar in underlying structure
• Example: A human arm, a porpoise flipper, an elephant leg,
and a bat wing have comparable internal bones
Vestigial Body Parts
• Body parts that have
no apparent function,
such as leg bones in
snakes and tail bones
in humans, were also
confusing
Vestigial Body
Parts
coccyx
leg
bones
A Pythons and boa constrictors have
tiny leg bones, but snakes do not walk.
B We humans use our legs, but
not our coccyx (tail bones). Fig. 16.4, p. 239
ANIMATION: Comparative pelvic anatomy
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Fossils
• Fossils of many animals that had no living representatives
were also discovered
• Deeper layers of rock held fossils of simple marine life; layers
above them held similar but more complex fossils
• fossil
• Remains or traces of an organism that lived in the ancient
past – physical evidence of ancient life
ANIMATION: Comparative anatomys
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16.3 A Flurry of New Theories
• In the 1800s, many scholars saw evidence of evolution and
realized that life on Earth had changed over time
• 19th century naturalists proposed theories such as
catastrophism and inheritance of acquired characteristics in
attempts to reconcile traditional beliefs with physical evidence
Key Terms
• catastrophism
• Now-abandoned hypothesis of Georges Cuvier, that
catastrophic geologic forces unlike those of the present
day shaped Earth’s surface
• evolution
• Change in a lineage, or descent with modification
• lineage
• Line of descent
Darwin and the HMS Beagle
• In 1831, the 22-year-old Charles Darwin set sail as a
naturalist aboard the Beagle, which circumnavigated the
globe over a period of five years
• Darwin’s detailed observations of geology, fossils, plants, and
animals encountered on this expedition changed the way he
thought about evolution
Voyage of the HMS Beagle
Theory of Uniformity
• On his voyage, Darwin read Charles Lyell’s Principles of
Geology, which gave him insights into the geologic history of
the regions he would encounter on his journey
• theory of uniformity
• Idea proposed by Lyell that, over great spans of time,
gradual, everyday geologic processes such as erosion
could have sculpted Earth’s current landscape
Charles Darwin
Key Concepts
• Emergence of Evolutionary Thought
• Nineteenth-century naturalists started to think about the
global distribution of species
• They discovered similarities and differences among major
groups, including those represented as fossils
16.4 Darwin, Wallace,
and Natural Selection
• Darwin’s observations of species in different parts of the world
helped him understand a driving force of evolution
• Charles Darwin and Alfred Wallace independently came up
with a theory of how environments also select traits
Old Bones and Armadillos
• Darwin noticed that fossils of extinct glyptodons from
Argentina had many traits in common with modern armadillos
• The idea that they possibly shared an ancestor helped Darwin
develop a theory of evolution by natural selection
Ancient Relatives
• A modern armadillo,
about a foot long
• Fossil glyptodon, an
automobile-sized
mammal that lived
between 2 million and
15,000 years ago
Competition for Limited Resources
• Thomas Malthus’s wrote that a population tends to grow until
it exhausts environmental resources
• As that happens, competition for those resources intensifies
among the population’s individuals
• Darwin realized that all populations, not just human ones,
must have the capacity to produce more individuals than their
environment can support
A Key Insight: Variation in Traits
• Darwin realized that in any population, some individuals have
traits that make them better suited to their environment than
others – and those traits might enhance the individual’s ability
to survive and reproduce (fitness)
• Adaptive traits (adaptations) that impart greater fitness to
an individual would become more common in a population
over generations, compared with less competitive forms
Key Terms
• fitness
• Degree of adaptation to an environment, as measured by
an individual’s relative genetic contribution to future
generations
• adaptation (adaptive trait)
• A heritable trait that enhances an individual’s fitness
Natural Selection
• Darwin considered the way humans select desirable traits in
animals by selective breeding (artificial selection)
• Darwin called the process in which environmental pressures
result in the differential survival and reproduction of
individuals of a population natural selection
• Darwin published On the Origin of Species, which laid out the
theory of evolution by natural selection
Key Terms
• artificial selection
• Selective breeding of animals by humans
• natural selection
• A process in which environmental pressures result in the
differential survival and reproduction of individuals of a
population who vary in details of shared, heritable traits
Principles of Natural Selection
Great Minds Think Alike
• Alfred Wallace studied
wildlife in the Amazon
and Malay Archipelago
• Before Darwin
published, Wallace
wrote an essay outlining
evolution by natural
selection—the same
theory as Darwin’s
Key Concepts
• A Theory Takes Form
• Evidence of evolution, or change in lines of descent, led
Charles Darwin and Alfred Wallace to independently
develop a theory of natural selection
• The theory explains how traits that define each species
change over time
ANIMATION: Finches of the Galapagos
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16.5 Fossils: Evidence of Ancient Life
• Fossils are remnants or traces of organisms that lived in the
past
• Most fossils are mineralized bones, teeth, shells, seeds,
spores, or other hard body parts
• Trace fossils such as footprints and other impressions, nests,
burrows, trails, eggshells, or feces are evidence of an
organism’s activities
Process of Fossilization
• Fossilization begins when an organism or its traces become
covered by sediments or volcanic ash
• After a very long time, pressure and mineralization
transform the remains into rock
• Fossils are found in stacked layers of sedimentary rock
• Younger fossils occur in more recent layers, on top of
older fossils in older layers
The Fossil Record
• Fossils are relatively rare, so the fossil record will always be
incomplete
• For a fossil of an extinct species to be found, at least one
specimen had to be buried before it decomposed or
something ate it
• The burial site had to escape destructive geologic events, and
it had to be a place accessible enough for us to find
The Ancient Lineage of Whales
• The fossil record holds clues to evolution:
• Ancestors of whales probably walked on land
• The skull and lower jaw have characteristics similar to
those of ancient carnivorous land animals
• With their artiodactyl-like ankle bones, Rodhocetus and
Dorudon were probably offshoots of the artiodactyl-tomodern-whale lineage
The Ancient Lineage of Whales
The Ancient Lineage of Whales
Fig. 16.9a, p. 244
The Ancient Lineage of Whales
A 30-million-year-old Elomeryx. This small terrestrial mammal
was a member of the same artiodactyl group that gave rise to
hippopotamuses, pigs, deer, sheep, cows, and whales.
Fig. 16.9a, p. 244
The Ancient Lineage of Whales
Fig. 16.9b, p. 244
The Ancient Lineage of Whales
B Rodhocetus, an ancient whale, lived about 47 million years ago. Its
distinctive ankle bones point to a close evolutionary connection to
artiodactyls.
Fig. 16.9b, p. 244
The Ancient Lineage of Whales
Fig. 16.9c, p. 244
The Ancient Lineage of Whales
C Dorudon atrox, an ancient whale that lived about 37 million years
ago. Its artiodactyl-like ankle bones were much too small to have
supported the weight of its huge body on land, so this mammal had
to be fully aquatic.
Fig. 16.9c, p. 244
The Ancient Lineage of Whales
Fig. 16.9d, p. 244
The Ancient Lineage of Whales
D Modern cetaceans such as the sperm whale have remnants of a
pelvis and leg, but no ankle bones.
Fig. 16.9d, p. 244
Radiometric Dating
• The half-life of a radioisotope allows us to determine the age
of rocks and fossils by radiometric dating
• half-life
• Characteristic time it takes for half of a quantity of a
radioisotope to decay
• radiometric dating
• Method of estimating the age of a rock or fossil by
measuring the content and proportions of a radioisotope
and its daughter elements
Radioisotopes
• Radioactive uranium 238 decays into thorium 234, and into
other elements until it becomes lead 206
• The half-life of uranium 238 to lead 206 is 4.5 billion years
• Recent fossils that still contain carbon can be dated by
measuring their carbon 14 content
• The half-life of 14C is 5,370 years
Radiometric Dating
• Half-life: The time it
takes for half of the
atoms in a sample of
radioisotope to decay
Radiometric Dating of a Fossil
•
14C
in CO2 enters food
chains through
photosynthesis
• Ratio of 14C to 12C is
used to calculate how
many half-lives passed
since the organism died
Radiometric Dating of a Fossil
B Long ago, trace amounts of 14C and a lot more 12C were incorporated
into the tissues of a nautilus. The carbon atoms were part of organic
molecules in the nautilus’s food. 12C is stable and 14C decays, but the
proportion of the two isotopes in the nautilus’s tissues remained the
same. Why? As long as it was alive, the nautilus continued to gain both
types of carbon atoms in the same proportions from its food.
Fig. 16.10b, p. 245
Radiometric Dating of a Fossil
C When the nautilus died, it stopped eating, so its body stopped gaining
carbon. The 12C atoms already in its tissues were stable, but the 14C atoms
(represented as red dots) were decaying into nitrogen atoms. Thus, over
time, the amount of 14C decreased relative to the amount of 12C. After 5,370
years, half of the 14C had decayed; after another 5,370 years, half of what
was left had decayed, and so on.
Fig. 16.10c, p. 245
Radiometric Dating of a Fossil
D Fossil hunters discover the fossil and measure its 14C and 12C
content—the number of atoms of each isotope. The ratio of those numbers
can be used to calculate how many half-lives passed since the organism
died. For example, if the 14C to 12C ratio is one-eighth of the ratio in living
organisms, then three half-lives (½)3 must have passed since the nautilus
died. Three half-lives of 14C is 16,110 years.
Fig. 16.10d, p. 245
Radiometric
Dating of a
Fossil
after one half-life
after two half-lives
B Long ago, trace amounts of 14C and a
lot more 12C were incorporated into the
tissues of a nautilus. The carbon atoms
were part of organic molecules in the
nautilus’s food. 12C is stable and 14C
decays, but the proportion of the two
isotopes in the nautilus’s tissues
remained the same. Why? As long as it
was alive, the nautilus continued to gain
both types of carbon atoms in the same
proportions from its food.
C When the nautilus died, it stopped
eating, so its body stopped gaining
carbon. The 12C atoms already in its
tissues were stable, but the 14C atoms
(represented as red dots) were decaying
into nitrogen atoms. Thus, over time,
the amount of 14C decreased relative to
the amount of 12C. After 5,370 years,
half of the 14C had decayed; after
another 5,370 years, half of what was
left had decayed, and so on.
D Fossil hunters discover the fossil and
measure its 14C and 12C content—the
number of atoms of each isotope. The
ratio of those numbers can be used to
calculate how many half-lives passed
since the organism died. For example, if
the 14C to 12C ratio is one-eighth of the
ratio in living organisms, then three
half-lives (½)3 must have passed since
the nautilus died. Three half-lives of 14C
is 16,110 years.
Stepped Art
Fig. 16.10, p. 245
ANIMATION: Radiometric dating
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ANIMATION: Radioisotope decay
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ABC Video: New Species of Pterodactyl