Download The Theory of Evolution

The Theory of Evolution
Chapter 15
Charles Darwin Proposed a Mechanism for
Evolution
• English naturalist. Born 1809 and died in
1882
• Darwin found evidence of evolution during
his voyage on the Beagle (419)
• he studied fossils, plants, and animals and
concluded that they changed over time
Jean Babtiste Lamarck also proposed a
mechanism for evolution
• French scientist
• proposed a mechanism for evolution
BEFORE Darwin in 1809
Jean Babtiste Lamarck also proposed a
mechanism for evolution
• According to Lamarck, evolution happened
to organisms through use and disuse
• happens within the organisms lifetime
• if used a lot a physical feature will become bigger
is not used smaller
• the traits are then passed on the to next
generation
• ex. giraffe necks
Darwin’s Theory of Natural Selection
• Natural Selection (420)
• “survival of the fittest” (not Darwin’s words but
Herbert Spencer’s)
• organisms with a particular trait are better suited
for their environment and survive, reproduce, and
pass that trait on to the next generation
• Natural Selection has four main principles:
Darwin’s Theory of Natural Selection
1. Individuals in a population of the same
species show variation
2. Variations are inherited
3. Organisms have more young than can
survive on available resources
4. Variations that increase reproductive
success will be more common in the next
generation
Darwin’s Theory of Natural Selection
• Darwin wrote the famous book On the
Origins of Species by Means of Natural
Selection about his work
• He continued to collect evidence to
support his theory for many years
Darwin’s theory of Natural Selection
• The heart of Darwin’s theory
lies in the concept of
adaptation
• Adaptation - changing of a
species that results in it
having a better chance to
survive in it’s environment
and reproduce
Choose an organism:
Describe 3 adaptations
Darwin’s Ideas Have Been Updated
• Scientists now know that DNA and genes
are involved
• Isolation – when two populations can not
breed – over time leads to different
species
• ex. Grand Canyon
squirrels (438)
Darwin’s Ideas Have Been Updated
• Extinction – species disappear completely
due to some environmental change
Evidence for Evolution
• Fossils – show a gradual changes of
organisms over time
• older fossils were near the bottom layers, newer
near the top
• organisms started out simple and gradually got
more complex
Evidence for Evolution
• Vestigial Structures – any body structure
that is reduced in function in a living
organism but was used by an ancestor
• wings in flightless birds (ostriches, emus,
penguins)
• hind limb bones in whales (285)
• appendix in humans
Evidence for Evolution
• Homologous Structures – structures that
share common ancestry
• forelimbs of humans, alligator, bird wing (287)
• Analogous Structures – Different
structures evolved for the same function
• wing of a bird and a wing of a butterfly
Evidence for Evolution
• Embryological Evidence – Similarity of the
structure of embryos of different species
• all vertebrate embryos have a tail and gill slits
during development (288)
Evidence for Evolution
• Comparative biochemistry
– Scientists can compare the number of DNA,
RNA, and amino acid sequences species have
in common
– The more they have in common the more
closely they are related
How Does Evolution Occur?
• Gradualism – gradual change over a long
period of time
• Punctuated Equilibrium – proposed by
American biologists Gould and Eldredge,
suggests long periods of no change and
short bursts of rapid change
Domesticated Fox Video
How Does Evolution Occur?
• Convergent Evolution – Distantly related
organisms evolve similar traits because of
similar environments
• Ex. Dolphins and sharks
• Divergent Evolution – Species evolve from
same ancestor and develop different
characteristics
Examples of Evolution
• Kettlewell’s study of peppered
moths
• most were light to match the tree
trunks covered with lichens, few
were dark
• after industrial revolution most
were black
• soot had turned the tree trunks
black making the dark moth better
suited for the environment –
natural selection
• What if there were no dark moths?
Examples of Evolution
• Galapagos Finches
• beak size was related to how wet or dry the
season was
• dry years large tough seeds needed to be eaten, in
wet yeasr smaller seeds were eaten