Charles Darwin developed the theory of evolution by natural selection based on observations he made during a 5-year voyage. He noticed that related species varied between locations and over time, suggesting descent from common ancestors. Darwin proposed that variations within species provided different adaptations for survival and reproduction, and that natural selection led populations to change over generations as favorable traits increased. His 1859 book On the Origin of Species outlined evolution based on struggle for existence, variation and adaptation, and survival of the fittest. Fossil, anatomical, embryological, and genetic evidence now provide strong support for evolution through natural selection.

1. S
Darwin’s Theory of
Evolution
Chapter 16

2. 16.1 Darwin’s Voyage of
Discovery
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.

3. 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.

4. S Jean Baptiste Lamarck, in 1809, proposed a
hypothesis of the inheritance of acquired
characteristics.
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
offspring.
S Lamarck’s hypothesis is now known to be
incorrect.

5. 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.

6. Observations
S Three patterns of biological diversity:
1. Species vary globally
2. Species vary locally
3. Species vary over time

7. Species Vary Globally
S Similar animals live in
separate, but similar
habitats.
Rheas – South America Ostrich - Africa

8. Species Vary Locally
S Different, yet related species occupied different habitats
in the same area.
Isabella Island Hood Island

9. Species Vary Over Time
S Fossils of extinct animals are similar to living species.

10. 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.

11. 16.3 Darwin Presents His
Case
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

12. Struggle for Existence
S Though every organism has the potential to produce
many offspring, only a limited number of those survive
and reproduce.
1 in 1000 survive to adulthood 50% survive past 1 year

13. Variation and Adaptation
S Individuals in a population vary in heritable characteristics
S Adaptations increase an organism’s ability to survive and
reproduce.
S Camouflage
S Mimicry
S Behaviors

14. 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.

15. Natural Selection
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. 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
takes place.
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
forms.
S Fossils are used to trace the evolution of modern
species from extinct species.

17. 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.

19. Comparing Anatomy and Embryology
S Homologous Structures
S Similarities in bone structure suggest that all vertebrates share a
common ancestor.

20. S Vestigial structures also provide evidence for evolution.
S Ex: hind limbs of whales and dolphins

21. Embryology
S At some time in their development all vertebrate embryos
have a tail, a notochord, and pharyngeal pouches.
S Suggesting common ancestry

22. Genetics and Molecular
Evidence
S Similarities in gene sequences can be linked to common
ancestry.
S Today we now know that genes are responsible for
inherited traits.
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

23. 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
antibiotics.
S Ex: TB, Staff