1. Descent with Modification: A Darwinian View of Life
Chapter 22
Descent with Modification: A Darwinian View of Life

2. Overview: Endless Forms Most Beautiful
A new era of biology began in 1859 when Charles Darwin published The Origin of Species
The Origin of Species focused biologists’ attention on the great diversity of organisms
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3. Darwin noted that current species are descendants of ancestral species
Evolution can be defined by Darwin’s phrase descent with modification
Evolution can be viewed as both a pattern and a process
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4. Scala Naturae and Classification of Species
The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae
The Old Testament holds that species were individually designed by God and therefore perfect
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5. Evolution is dna, nature, and TIME
Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose
Linnaeus was the founder of taxonomy, but he didn’t have a concept geologic time (millions to billions of years)
Evolution is dna, nature, and TIME
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6. Ideas About Change over Time
The study of fossils helped to lay the groundwork for Darwin’s ideas
Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata
Video: Grand Canyon
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7. Layers of deposited sediment Younger stratum with more recent fossils
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Figure 22.3 Formation of sedimentary strata with fossils
Older stratum
with older fossils

8. Lamarck’s Hypothesis of Evolution
Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
The mechanisms he proposed are unsupported by evidence
New interest with the understanding of epigenetics
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9. Fig. 22-4
Figure 22.4 Acquired traits cannot be inherited

10. Concept 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life
As the 19th century dawned, it was generally believed that species had remained unchanged since their creation
However, a few doubts about the permanence of species were beginning to arise
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11. Darwin’s Research
As a boy and into adulthood, Charles Darwin had a consuming interest in nature
Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University
After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle
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12. The Voyage of the Beagle
During his travels on the Beagle, Darwin collected specimens of South American plants and animals
He observed adaptations of plants and animals that inhabited many diverse environments
Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6000 years old
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13. Fig. 22-5 Figure 22.5 The voyage of HMS Beagle
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Marchena
Equator
SOUTH
AMERICA
Santiago
Daphne
Islands
Pinzón
AUSTRALIA
Fernandina
PACIFIC
OCEAN
Isabela
Figure 22.5 The voyage of HMS Beagle
For the Discovery Video Charles Darwin, go to Animation and Video Files.
Santa
Cruz
Andes
Cape of
Good Hope
Santa Fe
San
Cristobal
Tasmania
Florenza
Española
Cape Horn
New
Zealand
Tierra del Fuego

14. Darwin’s Focus on Adaptation
In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes
From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches
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15. (a) Cactus-eater (c) Seed-eater (b) Insect-eater Fig. 22-6
Figure 22.6 Beak variation in Galápagos finches
(b) Insect-eater

16. In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar
In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s
Darwin quickly finished The Origin of Species and published it the next year
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17. Darwin developed two main ideas:
The Origin of Species
Darwin developed two main ideas:
Descent with modification explains life’s unity and diversity
Natural selection is a cause of adaptive evolution
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18. Descent with Modification
Darwin never used the word evolution in the first edition of The Origin of Species
The phrase descent with modification summarized Darwin’s perception of the unity of life
The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past
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19. Fig. 22-8 Figure 22.8 Descent with modification Millions of years ago
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Figure 22.8 Descent with modification
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa) 34 24
5.5 2
104
Millions of years ago
Years ago

20. Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection
Darwin then described four observations of nature and from these drew two inferences
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21. Observation #1: Members of a population often vary greatly in their traits
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22. Fig
Figure Variation in a population

23. Observation #2: Traits are inherited from parents to offspring
Observation #3: All species are capable of producing more offspring than the environment can support
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24. Observation #4: Owing to lack of food or other resources, many of these offspring do not survive
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25. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
You might be more familiar with the phrase “survival of the fittest” : this refers to how many offspring you leave, not health or strength
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26. Evolution by natural selection
Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
Evolution by natural selection
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