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Chapter 17
Darwin and
Evolution
Darwin and
Evolution
Outline
History of Evolutionary Thought
Darwin’s Theory of Evolution
Earth very old
Descend with change from a common ancestor
Adaptation to a changing environment
The Evidence of Evolution
Fossil
Biogeographical
Anatomical
Biochemical
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Voyage of the HMS Beagle
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Charles Darwin at 31
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Darwin and
Evolution
History of Evolutionary Thought
Prior to Darwin
View of nature determined by deep-seated
beliefs
Held to be intractable truths
Biology thought had slowly begun to accept
- Various ideas of evolution
- Similarities between living things reflect recent
common ancestry
- Dissimilarities between living things reflect
ancient common ancestry
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Evolutionary Thought before Darwin
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Darwin and
Evolution
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Mid-Eighteenth Century
Taxonomy matured during mid-eighteenth
century
Linnaeus believed in:
- The fixity of species
- That each species had:
 An
ideal structure and function, and
 A place in the scala naturae (scale of complexity)
Count Buffon:
- Wrote 44-volume catalog of all known plants
and animals
- Suggested descent with modification
Darwin and
Evolution
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Late Eighteenth Century
Cuvier:
First to use comparative anatomy to develop a
system of classification
Founded Paleontology
Proposed Catastrophism
- Local catastrophes in past had caused later
strata to have a new mix of fossils
- After each catastrophe, the region was
repopulated by species from surrounding areas
Darwin and
Evolution
Late Eighteenth Century
Lamarck:
First biologist to:
- Propose evolution
- Link diversity with environmental adaptation
Concluded more complex organisms are descended
from less complex organisms
Proposed inheritance of acquired characteristics –
Lamarckianism
Charles Lyell:
Earth is subject to slow but continuous cycles of
erosion and uplift
Proposed uniformitarianism, rates and processes of
change are constant
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Formation of Sedimentary Rock
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Darwin and
Evolution
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Darwin’s Theory of Evolution
Geological observations consistent with
those of Hutton & Lyell
Biogeographical observations:
The study of the geographic distribution of life
forms on earth
Darwin saw similar species in similar
habitats;
Reasoned related species could be modified
according to the environment
A Glyptodont and a Giant Sloth
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The Patagonian Hare,
Dolichotis patagonium
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Darwin and
Evolution
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Galápagos Islands
Tortoises
Darwin observed tortoise neck length varied
from island to island
Proposed that speciation on islands
correlated with a difference in vegetation
Finches
Darwin observed many different species of
finches on various islands
Speculated they could have descended from a
single pair of mainland finch
Galápagos Tortoises, Geochelone
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Galápagos Finches
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Darwin and
Evolution
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Natural Selection and Adaptation
Individuals have heritable variations
More individuals produced each generation
than environment can support
Some individuals have adaptive
characteristics
Enables increased survival and reproduction
Increasing proportion of succeeding
generations will have these characteristics
Populations become adapted to their local
environment through change in individuals
Variation in a Population
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Darwin and
Evolution
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Organisms Have Variations
Darwin emphasized that individuals from a
population vary in their:
Functional characteristics
Physical characteristics
Behavioral characteristics
Proposed that these variations:
Are essential
Allow adaptation to the environment over time
Artificial Selection of Animals
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Artificial Selection of Plants
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Darwin and
Evolution
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Organisms Struggle to Exist
Malthus
Each generation has the same reproductive
potential as the previous generation
- Reproductive potential is greater than
environment can support
- Death, disease, and famine were inevitable if
population were to have stability
Individuals experience a constant struggle for
survival
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Evolution
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Organisms Differ in Fitness
Fitness is the relative reproductive success of
an individual
The most-fit individuals in a population
capture a disproportionate share of goodies
Interactions with the environment determine
which individuals reproduce the most
Adaptation
Changes that help a species become more
suited to its environment
Product of natural selection
Transitional Fossils
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The Evidence of Evolution:
Anatomical
Darwin and
Evolution
Vertebrate forelimbs:
Homologous - All contain the same sets of
bones in similar ways
Yet they are modified extensively to meet
various adaptive needs
Darwin interpreted this as support for a
hypothesis of common descent
Embryological development
All vertebrate embryos have:
A postanal tail and
Paired pharyngeal (gill) pouches
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Biogeography
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The Evidence of Evolution:
Anatomical
Darwin and
Evolution
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Homologous Structures:
Anatomically similar because they are inherited from
a common ancestor
May be functionally similar or not
Analogous Structures:
Serve the same function
Not constructed similarly
Do not share a common ancestor
Vestigal Structures:
Fully-developed anatomical structures
Reduced or obsolete function
Significance of Homologous Structures 28
Significance of Developmental Similarities29
Vestigial Limbs in Whales
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The Evidence of Evolution:
Fossil & Biogeographical
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Evolution
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Fossil Evidence
Fossils record the history of life from the past
Document a succession of life forms from the
simple to the more complex
Sometimes the fossil record is complete
enough to show descent from an ancestor
Biogeographical
Distributions of plants and animals across
earth
Consistent with origin in one locale and then
spread to accessible regions
Darwin and
Evolution
Biochemical Evidence
Almost all living organisms:
Use the same basic biochemical molecules
Utilize same DNA triplet code
Utilize same 20 amino acids in their proteins
DNA base-sequence differences:
When very similar, suggest recent common
descent
When more different, suggest more ancient
common descent
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Significance of
Biochemical Differences
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Darwin and
Evolution
Review
History of Evolutionary Thought
Darwin’s Theory of Evolution
Earth very old
Descend with change from a common ancestor
Adaptation to a changing environment
The Evidence of Evolution
Fossil
Biogeographical
Anatomical
Biochemical
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Ending Slide Chapter 17
Darwin and
Evolution