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Theory of Evolution
Chapter 15
15.1 Key Concepts
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What was Charles Darwin’s contribution of
science?
What pattern did Darwin observe among
organisms of the Galapagos Islands?
15-1 The Puzzle of Life’s Diversity
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Biological diversity- variety of living things
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How did they arise? Related?
Evolution- change over time; process by
which modern organisms have descended
from ancient organisms
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Theory- well-supported testable explanation
of phenomena that have occurred in the
natural world
Charles Darwin
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Charles Darwin (1809-1882)Englishman
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Voyage aboard H.M.S. Beagle (1831)
During his travels, Darwin made numerous
observations and collected evidence that led
him to propose a revolutionary hypothesis
about the way life changes over time
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Collected plant and animal specimens while ship
was anchored
Darwin’s Observations
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Well suited for environment
Many ways for survival and production of
offspring
Puzzled by where species lived and did not live
Gathered fossils
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Resembled organisms still alive
Others looked completely different
Galapagos Islands were very close together, but
had very different climates
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Tortoise shells
Journey Home
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Time spent thinking
Darwin observed that the characteristics
of many animals and plants varied
noticeably among the different islands of
the Galapagos
15-2 Ideas That Shaped Darwin’s Thinking
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Fossils caused Darwin to be skeptical of
people’s views
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Earth created only a few thousand years ago
Robin had always been a robin
Discoveries challenged fundamental
beliefs held at that time
Lyell and Hutton
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James Hutton
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Earth had to be much more than a few thousand years old
1795, hypothesis about geological forces that have shaped Earth
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Internal forces- mountains, valleys, rocks- affected by natural forcesrain, wind, heat and cold temps
Charles Lyell
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Gave book to Darwin
Processes that shaped the Earth millions of years earlier continue in
present
Fossils of marine animals above sea level
Influence?: If the Earth could change over time, might life change as
well?
It would have taken many, many years for life to change in the way
he suggested. This would have been possible only if the Earth were
extremely old
Jean- Baptiste Lamarck
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Living things have changed over time
1809- hypothesis (1st to develop)
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Tendency toward perfection- continually changing
and acquiring features that help them live more
successfully in their environments
Use and disuse- organisms could alter the size or
shape of particular organs by using their bodies in
new ways
Inheritance of acquire traits- pass on traits to
offspring
Evaluation of hypothesis
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Did not know how traits are inherited
Did not know that behavior has no effect on heritance
Thomas Malthus
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1798- human population
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Reasoned that if the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space and food for everyone
Influence
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What causes death of so many individuals?
What factor/factors determine which ones
survive and reproduce, and which do not?
15-3 Darwin Presents His Case
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1858- Alfred Wallace sent short essay
which contained thoughts on evolutionary
change
1859- Darwin publishes his book On the
Origin of Species
Inherited Variation and Artificial Selection
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Inherited variation- differences that are passed
from parents to offspring
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Larger fruits on plants; some cows give more milk
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Today: caused by variations in their genes
Then: revolutionary idea because variations thought to be
minor defects
Artificial selection- selection by humans for
breeding of useful traits from the natural
variation among different organisms
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Animal breeders used heritable variation to improve
livestock and crops
Evolution by Natural Selection
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Malthus- high birth rates and shortage of
life’s basic needs would eventually force
organisms into a competition for resources
Survival of the Fittest
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Fitness- ability of an individual to survive and
reproduce in its specific environment
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Result of adaptation- any inherited characteristic
that increases an organism’s chance of survival
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Can be anatomical (structural) or physiological
(functions)
Evolution by Natural Selection
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Central to process of evolution by natural
selection
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Individuals compete to survive and produce offspring
 Low levels of fitness = death
 High levels of fitness = survival
Survival of the fittest (natural selection)- process
by which individuals that are better suited to
their environment survive and reproduce most
successfully (takes place without human control
or direction)
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Can only be seen in time over successive generations
Only certain individuals of a population produce new
individuals
Descent with Modification
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Principle that each living species
descended with changes, from other
species over time
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Look different from ancestors
Implies that all living organisms are related to
one another
Common descent- principle that all species
were derived from common ancestors
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“Tree of life” links all living things
Evidence of Evolution
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Fossil Record
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Fossils = record of history of Earth
Compare fossils of older rock layers and fossils of
younger rock layers told us that life on Earth has
changed over time
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# of fossils has increased since Darwin, but we still have
gaps
Geographic Distribution
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Finches- similar but distinctly different
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Slightly different from mainland (S. America)
Same ancestor with modifications
Different species on continents of S. America and
Australia
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Similar environments = similar features; different ancestors
Evidence of Evolution
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Homologous Body Structures
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Limbs vary greatly in form and function, yet
constructed from same basic bones
Homologous structures- structures that have different
mature forms but develop from the same embryonic
tissue
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Descent with modification
Group organisms to how recently they last shared a
common ancestor
Vestigial organ- organ that serves no useful function
in an organism
Embryology
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Early stages, or embryos, of many animals
with backbones are very similar
The same groups of embryonic cells
develop in the same order and in similar
patterns to produce the tissues and
organs of all vertebrates
Summary of Darwin’s Theory
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Individual organisms differ, and some of
this variation is heritable
Organisms produce more offspring than
can survive, and many that do survive do
not reproduce
Because more organisms are produced
than can survive, they compete for limited
resources