Endless Forms Most Beautiful

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AP Biology, Chapter 22

Descent with Modification: A Darwinian View of Life
Endless Forms Most Beautiful

1. State the two major points that Charles Darwin made in The Origin of Species concerning

Earth's biota.

Current organisms evolved from ancestral species

Natural selection is a mechanism for evolution

22.1 The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

Scala Naturae and Classification of Species

2. Correlate Aristotle's scala naturae and the Abrahamic view of the fixity of species.


Organisms occupy rungs on a scale of complexity

Already perfectly adapted, so unchanging


Species created by a higher being

Designed perfect already

3. Describe Carolus Linnaeus's contribution to Darwin's theory of evolution.

"Founded" taxonomy

Grouped organisms hierarchically by shared physical traits

Unintentionally created a system for identifying evolutionary kinship

Ideas About Change over Time

4. Describe Georges Cuvier's contribution to paleontology.

Scientifically documented the fossils in the Parisian rockpile

Concluded: the deeper, the older, the more different the fossils

Recognized the extinction of species

5. Explain how Cuvier and his followers used the concept of catastrophism to oppose the

theory of evolution.

Averred catastrophes defined strata

Said different organisms in overlying strata hadn't evolved but migrated

6. Explain how the principle of gradualism and Charles Lyell's theory of uniformitarianism

influenced Darwin's ideas about evolution.


Current gradual processes can explain land forms

Deep time: Earth millions and millions of years old


Uniformitariamism: mechanisms are constant over time

= the opposite of catastrophism

Darwin proposed evolution by slow, gradual change

Lamarck’s Hypothesis of Evolution

7. Describe Jean Baptiste Lamarck's model for how adaptations evolve. Explain the

challenges to Lamarck's ideas with respect to current understandings of biology.

Recognized descent with modification in the fossil record

Wrong mechanism

Innate drive to become more complex

Species change, become better adapted, by use and disuse

Acquired characteristics passed to offspring

22.2 Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life


Darwin’s research


The Voyage of the Beagle

8. Describe how Darwin used his observations from the voyage of the HMS Beagle to formulate and support his theory of evolution.

South American species resembled one another

Observations suggested an old, constantly changing Earth

Related species on the Galapagos were adapted to local environments

Darwin’s Focus on Adaptation

9. How did Darwin’s view of adaptation inform his hypothesis?

Adaptation: trait enhancing survival and reproduction

Adaptations therefore passed on as a result

10. Describe how Lyell and Alfred Russel Wallace influenced Darwin.

Lyell: urged Darwin to publish

Wallace: sent manuscript in 1858; matched Darwin's unpublished work

The Origin of Species


Descent with Modification

11. Explain what Darwin meant by "descent with modification."

All life originated from a single, unknown prototype

Descendents spread and became adapted to new habitats

Branching from common ancestors

Saw Linneaus’ hierarchical taxonomy as evolutionary history

Artificial Selection, Natural Selection, and Adaptation

12. Distinguish between artificial selection and natural selection.

Artificial is human-directed selective breeding

Natural is differential survival based in variability of useful traits

13. Describe the three inferences Darwin made from his observations that led him to propose natural selection as a mechanism for evolutionary change.

Variation in heritable traits differential survival

Exponential growth + limited resources struggle for existence

Small changes over generations adaptation of populations

14. Explain how an essay by the Rev. Thomas Malthus influenced Charles Darwin.

Malthus, 1798, An Essay on the Principle of Population

Populations grow exponentially, resources don't

Darwin incorporated that as differential survival

15. Explain why the population is the smallest unit that can evolve.

Individuals are tested during their lifetime

Populations record the results when they are gone

Natural Selection: A Summary

22.3 Evolution is supported by an overwhelming amount of scientific evidence


Direct Observations of Evolutionary Change

Natural Selection in Response to Introduced Plant Species

The Evolution of Drug-Resistant Bacteria

16. Using some contemporary examples, explain how natural selection results in

evolutionary change.

Galapagos finch beak shape changes in response to food change

Antibiotic resistant bacteria predominate with overuse

Transplanted guppy size increases in response to predator



17. Explain how homologous structures support Darwin's theory of natural selection.

Homology: similarity inherited from a common ancestor

Anatomical and Molecular Homologies

Ex: homologous structures of vertebrate forelimbs

Ex. embryonic structures

Ex.: vestigial structures; remnants of structures useful in other species

Ex.: similar DNA and protein sequences

Homologies and “Tree Thinking”

18. How are homologous groupings expressed in evolutionary trees?

Branch points = common ancestors with a trait

All branches from that point had the trait

Usually correlated with multiple types of data

A Different Cause of Resemblance: Convergent Evolution

19. Contrast homologous and analogous structures and account for convergent evolution.


Structures inherited from a common ancestor

Ex>; amniote embryonic membranes


Structures developed independently

Ex.: wings of birds, butterflies

Convergent evolution

Evolution of the same adaptation in response to the same pressure

Ex.: gliding in flying squirrels and sugar gliders

The Fossil Record

20. How does the fossil record document the patterns of evolution?

Lineages of major groups show acquisition and alteration of homology

Sufficient transitional forms are present


21. Explain how biogeography supports the evolutionary deductions based on homologies.

Group origins and spreading patterns parallel the evolution of continents

Islands contain related endemic species

What is Theoretical About Darwin’s View of Life?

22. Explain the problem with the statement that Darwinism is "just a theory." Distinguish

between the scientific and colloquial use of the word "theory."

Evolution is based on a vast amount of historical evidence

Commonly "theory" is used as scientists use "hypothesis"

Darwin's proposed mechanism is theoretical

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