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16.1 Darwin’s Voyage of
S Charles Darwin
S Born Feb 12, 1809
S The first person to publish convincing evidence that species
evolve, and propose a reasonable mechanism explaining
how evolution occurs.
S Modern organisms evolved over long periods of time through
decent from common ancestors.
Science Before Darwin
S In Darwin’s time, most people and scientists believed that
each species exists, unchanged as it has for all time.
S However, views were beginning to change dramatically
S The Earth had changed along with all living things on Earth
S With the discovery of more and more fossils scientists
began to propose various mechanisms to explain how
these species change over time.
S Jean Baptiste Lamarck, in 1809, proposed a
hypothesis of the inheritance of acquired
S This hypothesis stated that by use or disuse of a
body part could cause change in that feature
within the lifetime of the organism.
S These changes would then be passed on to
S Lamarck’s hypothesis is now known to be
Darwin’s Epic Journey
S In 1831, at age 22, Darwin took a position as a naturalist on
a voyage of the HMS Beagle.
S On the Beagle’s 5-year journey it sailed around the world to
map the coast of South America.
S During the voyage Darwin found evidence that challenged the
belief that species are unchanging.
S Three patterns of biological diversity:
1. Species vary globally
2. Species vary locally
3. Species vary over time
Species Vary Globally
S Similar animals live in
separate, but similar
Rheas – South America Ostrich - Africa
Species Vary Locally
S Different, yet related species occupied different habitats
in the same area.
Isabella Island Hood Island
Species Vary Over Time
S Fossils of extinct animals are similar to living species.
Putting it Together
S Darwin noticed that the finches on each of the Galápagos
islands had differently shaped beaks, and were similar to
those in South America.
S He spent years researching his ideas after he returned.
S He began to wonder if the animals living on the different
islands had come from a common ancestor.
16.3 Darwin Presents His
S In 1858 Darwin published his ideas in the
book “On the Origin of Species.”
S This book outlined Darwin’s ideas of
evolution based on natural selection
focusing on three principles:
S The struggle for existence
S Variation and Adaptation
S Survival of the fittest
Struggle for Existence
S Though every organism has the potential to produce
many offspring, only a limited number of those survive
1 in 1000 survive to adulthood 50% survive past 1 year
Variation and Adaptation
S Individuals in a population vary in heritable characteristics
S Adaptations increase an organism’s ability to survive and
Survival of the Fittest
S Fitness is how well an organism can survive and
reproduce in its environment.
S Individuals with a high fitness are well suited for their
environment and are more likely to survive and reproduce.
S Individuals with low fitness are not as well suited to their
environment therefore will either die or leave few offspring.
S These mechanisms allow for natural selection to occur.
S Each generation populations continue to change as more
individuals are born with favorable traits for the environment.
S It is important to remember that if environmental
conditions change faster than a species can adapt to the
changes, the species may become extinct.
S Example p. 462
16.4 Evidence of Evolution
The Age of the Earth and The Fossil Record
S Earth is 4.5 billion years old
S Fossils provide the most direct evidence that evolution
S Fossils are preserved or mineralized remains or imprint of
an organism that lived long ago.
S Fossils provide an actual record of Earth’s past life
S Fossils are used to trace the evolution of modern
species from extinct species.
S Although the fossil record is not, and will never, be
complete it presents strong evidence that evolution
has taken place.
S Paleontologists analyze fossils by dating the rocks
and minerals around it.
S They can arrange the fossils from oldest to
youngest, and in this, orderly patterns of evolution
can be seen.
Comparing Anatomy and Embryology
S Homologous Structures
S Similarities in bone structure suggest that all vertebrates share a
S Vestigial structures also provide evidence for evolution.
S Ex: hind limbs of whales and dolphins
S At some time in their development all vertebrate embryos
have a tail, a notochord, and pharyngeal pouches.
S Suggesting common ancestry
Genetics and Molecular
S Similarities in gene sequences can be linked to common
S Today we now know that genes are responsible for
S Traits become more common in a population because more
individuals in the population carry the alleles for those forms.
S Mutations and the recombination of alleles that occurs during
sexual reproduction provide endless sources of new variations
for natural selection to act upon.
S Analyzing Data p.470
Examples of Evolution
Natural Selection at Work
S The key lesson scientists have learned about evolution by
natural selection is that the environment dictated the direction
and amount of change.
S Ex: The polar bear’s white fur enables it to hunt successfully
in its snowy environment. In a warmer environment, having
white fur would no longer be an advantage.
Examples of Natural Selection
S Bacteria that cause disease evolve to have resistance to
S Ex: TB, Staff