www.cengage.com/biology/starr
Albia Dugger • Miami Dade College
Cecie StarrChristine EversLisa Starr
Chapter 16Evidence of Evolution
(Sections 16.6 - 16.9)
16.6 Putting Time Into Perspective
• Transitions in the fossil record are boundaries for great intervals of the geologic time scale
• geologic time scale • Chronology of Earth’s history• Correlates geologic and evolutionary events
The Geologic Time Scale
Sedimentary Rock in the Grand Canyon
ANIMATION: Geologic time scale
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Key Concepts
• Evidence From Fossils• The fossil record provides physical evidence of past
changes in many lines of descent• We use the property of radioisotope decay to determine
the age of rocks and fossils
16.7 Drifting Continents,Changing Seas
• The theory that all continents today were once part of the supercontinent Pangea explains why the same fossils occur in sedimentary rock on both sides of the Atlantic Ocean
• Pangea • Supercontinent that formed about 237 million years ago
and broke up about 152 million years ago
Plate Tectonics
• Movements of Earth’s tectonic plates carry land masses to new positions, which have profound impacts on evolution
• plate tectonics •Theory that Earth’s outer layer of rock is cracked into plates, the slow movement of which rafts continents to new locations over geologic time•Supported by magnetic polarity of igneous rocks
Mechanisms of Plate Tectonics
• New crust spreads outward from oceanic ridges, forcing tectonic plates away from the ridge and into trenches
Fig. 16.12.1-4, p. 248
fault hot spottrench trenchridge123 4
Mechanisms of Plate Tectonics
ANIMATION: Plate margins
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An Older Supercontinent
• Identical layers of rock around the Southern Hemisphere hold matching fossils of organisms that were extinct millions of years before Pangea formed
• An older supercontinent, Gondwana, included most land masses that are now in the Southern Hemisphere, India and Arabia
• Gondwana • Supercontinent that existed before Pangea, more than 500
million years ago
The Drifting Continents
• Major evolutionary forces: •Gondwana broke up in the Silurian•Pangea formed in the Triassic, broke up in the Jurassic
Key Concepts
• Evidence From Biogeography• Geologic events have influenced evolution• Correlating geologic and evolutionary events helps explain
the distribution of species, past and present
16.8 Similarities in Body Form and Function
• Clues about the history of a lineage may be found in body form, function, or biochemistry
• Similarities in structure of body parts often reflect shared ancestry – in such cases, comparative morphology can be used to unravel evolutionary relationships
Morphological Divergence
• Homologous structures (body parts that appear different in different lineages, but are similar in some underlying aspect of form) are evidence of a common ancestor
• Body parts become modified to a different size, shape, or function in different lineages by morphological divergence
• Example: Limb bones of all modern land vertebrates originated from a family of ancient “stem reptiles”
Key Terms
• homologous structures • Similar body parts that evolved in a common ancestor
• morphological divergence• Evolutionary pattern in which a body part of an ancestor
changes in its descendants
Morphological Divergence
• Number and position of many skeletal elements were preserved when diverse forms evolved
• Certain bones were lost over time in some of the lineages
Fig. 16.14, p. 250elephant
human
bat
porpoise
penguin
chicken
pterosaur
stem reptile5
123
4
5
12
34
5
12
3 4
1
2 3
32
54
2
3
1
4
23
1
Morphological Divergence
Morphological Convergence
• Analogous structures are body parts that look alike in different lineages but did not evolve in a common ancestor
• They evolved separately after the lineages diverged (as adaptations to the same environmental pressures) by the process of morphological convergence
• Example: Bird, bat, and insect wings all perform the same function (flight) but the wing structures are not homologous
Key Terms
• analogous structures • Similar body structures that evolved separately in different
lineages
• morphological convergence • Evolutionary pattern in which similar body parts evolve
separately in different lineages
Morphological Convergence
Fig. 16.15a, p. 251
Morphological Convergence
Fig. 16.15b, p. 251
Morphological Convergence
Fig. 16.15c, p. 251
Morphological Convergence
Fig. 16.15d, p. 251
Morphological Convergence
Fig. 16.15d, p. 251
Insects Bats Humans Crocodiles Birds
wings
wings wings
limbs with 5 digitsD
Morphological Convergence
16.9 Similarities in Patterns of Development
• Similar patterns of embryonic development reflect shared ancestry
• Master genes that control embryonic development patterns have changed very little or not at all over evolutionary time
• Master genes with similar sequence and function in different lineages are strong evidence that those lineages are related
Similar Genes in Plants
• Master genes called homeotic genes guide formation of specific body parts during development
• Example: The Apetala1 gene affects formation of petals across many different lineages, so this gene probably evolved in a shared ancestor
Developmental Comparisons in Animals
• Embryos of many vertebrate species develop in similar ways
• All vertebrates go through a stage in which they have four limb buds, a tail, and a series of somites
Fig. 16.16a, p. 252
Developmental Comparisons in Animals
Fig. 16.16b, p. 252
Developmental Comparisons in Animals
Fig. 16.16c, p. 252
Developmental Comparisons in Animals
Fig. 16.16d, p. 252
Developmental Comparisons in Animals
Fig. 16.16e, p. 252
Developmental Comparisons in Animals
Variations in Development
• Differences are brought about by variations in expression patterns of master genes that govern development
• Example: • The pattern of expression of Hox master genes
determines particular zones along the body axis• In insects, the Hox gene antennapedia, determines where
legs develop on the thorax• A vertebrate version of antennapedia, the Hoxc6 gene,
causes a vertebra to develop ribs as part of the back
Expression of Antennapedia
• A mutation that causes antennapedia to be expressed in embryonic tissues of a Drosophila’s head (left) causes legs to form there too (right)
Fig. 16.17a, p. 252
Expression of Antennapedia
Fig. 16.17b, p. 252
Expression of Antennapedia
Expression of Hox6
• Chicks (left) have 7 vertebrae in their back and 14-17 in their neck; snakes (right) have more than 450 back vertebrae
Forever Young
• Mutations that alter rate of development may allow juvenile traits to persist into adulthood
• Example:• At early stages of development, chimpanzee and human
skulls appear quite similar• Different parts develop at different rates• A human adult skull is proportioned more like the infant
chimpanzee skull than the adult chimpanzee skull
Proportional Changes During Skull Development
Fig. 16.19, p. 253
proportions in infant
proportions in infantadult
adult
A
B
Proportional Changes During Skull Development
Fig. 16.19a, p. 253
Proportional Changes During Skull Development
Fig. 16.19a, p. 253
proportions in infantadult
A
Proportional Changes During Skull Development
Fig. 16.19b, p. 253
Proportional Changes During Skull Development
Fig. 16.19b, p. 253
proportions in infant adultB
Proportional Changes During Skull Development
ANIMATION: Mutation and proportional changes
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Key Concepts
• Evidence in Form and Function• Different lineages may have similar body parts that reflect
descent from a shared ancestor• Lineages with common ancestry often develop in similar
ways
Reflections of a Distant Past (revisited)
• The K–T boundary layer, an unusual clay that formed 65 million years ago, is rich in iridium, an element rare on Earth’s surface but common in asteroids
• Scientists found a huge crater, about 65 million years old, off the coast of Mexico’s Yucatán Peninsula – evidence of an asteroid impact that may have caused extinctions