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Darwin’s Theory of
Evolution
Biology 1 2009-2010
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Diversity
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Diversity
Evolution is the process by which modern organisms
have descended from ancient organisms.
A scientific theory is a well-supported testable
explanation of phenomena that have occurred in the
natural world.
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Voyage of the Beagle
Voyage of the Beagle
In 1831, Darwin set sail from England aboard the
H.M.S. Beagle for a voyage around the world.
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Voyage of the Beagle
During his travels, Darwin made
numerous observations and collected
evidence that led him to propose a
hypothesis about the way life changes
over time.
That hypothesis has become the theory of
evolution (aka theory of natural selection).
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Darwin's Observations
Darwin's Observations
• He observed many plants and animals were well
suited to the environments they inhabited.
•He was impressed by the ways in which
organisms survived and produced offspring.
•Darwin was puzzled by where different species
lived and did not live.
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Darwin's Observations
Living Organisms and Fossils
Darwin collected the preserved remains of ancient
organisms, called fossils.
Some of those fossils resembled organisms that
were still alive.
Others looked completely unlike any creature he
had ever seen.
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Darwin's Observations
The Galápagos Islands
Darwin observed that the Galápagos Islands were
close together but had very different climates.
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The Journey Home
Darwin observed that the characteristics
of many animals and plants varied
noticeably among the different islands of
the Galápagos.
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The Journey Home
Darwin wondered if animals living on different islands
had once been members of the same species.
These separate species would have evolved from an
original South American ancestor species.
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An Ancient, Changing Earth
Hutton and Lyell helped scientists recognize that
Earth is many millions of years old, and the
processes that changed Earth in the past are the
same processes that operate in the present
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An Ancient, Changing Earth
This understanding of geology influenced
Darwin:
• If the Earth could change over time, life might
change as well.
• It would have taken many years for life to change
in the way Lyell suggested.
This would have been possible only if the Earth were
extremely old.
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Lamarck's Evolution Hypotheses
Lamarck's Evolution Hypotheses
Jean-Baptiste Lamarck
recognized that:
• living things have changed
over time.
• all species were
descended from other
species.
• organisms were adapted
to their environments.
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Lamarck's Evolution Hypotheses
Lamarck proposed that by selective use or disuse
of organs, organisms acquired or lost certain traits
during their lifetime. These traits could then be
passed on to their offspring. Over time, this
process led to change in a species.
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A male fiddler
crab uses its front
claw to ward off
predators and to
attract mates.
Lamarck's Evolution Hypotheses
Lamarck's Hypothesis
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Because the front
claw is used
repeatedly, it
becomes larger.
Lamarck's Evolution Hypotheses
Lamarck's Hypothesis
This characteristic
(large claw) is
passed onto its
offspring.
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Lamarck's Evolution Hypotheses
Evaluating Lamarck's Hypotheses
Lamarck’s hypotheses of evolution are
incorrect in several ways.
Lamarck did not know:
• how traits are inherited.
• that an organism’s behavior has no effect on
its heritable characteristics.
However, he paved the way for the work of later
biologists.
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Publication of On the Origin of
Species
In 1859, Darwin published his book, On the Origin
of Species.
• proposed a mechanism for evolution called
natural selection.
• presented evidence that evolution has been
taking place for millions of years—and continues
in all living things.
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Inherited Variation and Artificial
Selection
Darwin noted that plant and
animal breeders would breed
only the largest hogs, the
fastest horses, or the cows
that produced the most milk.
Darwin termed this process
artificial selection.
Artificial selection is the
selection by humans for
breeding of useful traits from
the natural variation among
different organisms.
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Evolution by Natural Selection
Survival of the Fittest
The ability of an individual to survive and
reproduce in its specific environment is fitness.
Darwin proposed that fitness is the result of
adaptations.
An adaptation is any inherited characteristic that
increases an organism's chance of survival.
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Evolution by Natural Selection
Because of its similarities to artificial selection,
Darwin referred to the survival of the fittest as
natural selection.
In natural selection, the traits being selected
contribute to an organism's fitness in its
environment.
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Evolution by Natural Selection
Over time, natural selection results in changes in
the inherited characteristics of a population.
These changes increase a species' fitness in
its environment.
Each living species has descended, with
changes, from other species over time.
Darwin referred to this principle as descent with
modification.
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Evidence of Evolution
Evidence of Evolution
Darwin argued that living things have
been evolving on Earth for millions of
years. Evidence for this process include:
•the fossil record
•geographical distribution
•homologous structures
•similarities in early development, or
embryology.
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Evidence of Evolution
The Fossil Record
Darwin saw fossils as a record of the history of life
on Earth.
By comparing fossils from older rock layers with
fossils from younger layers, scientists could
document that life on Earth has changed over
time.
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Evidence of Evolution
Geographical Distribution
Similar, But Unrelated
Species
an
d
an
d
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Evidence of Evolution
Homologous Body Structures
Structures that have different mature forms but
develop from the same embryonic tissues are
called homologous structures.
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Evidence of Evolution
Not all homologous structures serve important
functions.
The organs of many animals are so reduced in size
that they are just vestiges, or traces, of homologous
organs in other species.
These organs are called vestigial organs.
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Evidence of Evolution
Similarities in Embryology
The 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.
Pharyngeal
pouches
Post-anal
tail
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Chick embryo (LM)
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Human embryo
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