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Darwin Presents His Case
Section 15.3 – Darwin Presents His
Case
1. A species is a group of organisms that can:
• successfully reproduce
• produce offspring that are fertile
2. Variation = differences between organisms
of a population. 2 sources:
• sexual reproduction and gene shuffling
during Meiosis (sperm + egg)
• mutation
3. Adaptations:
•
•
•
a variation that increases an organism’s chances
of survival
“all adaptations are variations”
“not all variations are adaptations”
4. A niche is:
•
•
not something you scratch
the job an animal does in its environment
Decomposer
Predator
(heterotroph)
(heterotroph)
Consumer
Producer(heterotroph)
(autotroph)
5. Fossils:
•
•
•
preserved remains or imprints of ancient
organisms
usually requires organisms to become buried in
sediment
organism and sediment are compressed into rock
Evolution is:
• a change in a population of
organisms over time
• it NEVER states that humans
came from monkeys
Ideas That Influenced Darwin
Geology
Scientists were discovering that the world
was a lot older than people thought
(Hutton, Lyell)
Artificial Selection
Farmers were changing the characteristics
of their animals and crops by breeding
the ones with the best features
Population Control
Evidence was pointing to the fact that
humans may soon outgrow the food
supply (Malthus)
One of the First Ideas About
Evolution
•
The Inheritance of Acquired Characteristics
(Lamarck)
The Inheritance of Acquired
Characteristics (Lamarck)
1)
2)
3)
4)
Organisms try to “improve” themselves
The most used parts develop
The least use parts waste away
Developed parts can be passed on to children
Section 15.3 – Darwin Presents His
Case: Evolution by Natural Selection
• Darwin’s idea revolved around VARIATION (new
or different features)
• Variations come from:
• Mutations (usually , sometimes good)
• Different combinations of features from sexual
reproduction / meiosis
Adaptations:
•
•
•
a variation that increases an organism’s chances
of survival
“all adaptations are variations”
“not all variations are adaptations”
Artificial Selection
• One of Darwin’s best insights was that not only
is there variation in nature, but that farmers had
been taking advantage of this for centuries
• Humans take advantage of these variations to
create organisms with the features we like best
• Darwin figured the same thing happens in the
wild, but with NATURE SELECTING which
organisms live and die
Main Points of Natural Selection
1) Populations Have Variations (Everyone is
Different)
2) Some Variations Are Favorable (called
Adaptations)
3) More Babies Are Produced Than Can
Survive (Competition / Struggle for
Existence)
4) Those With Favorable Variations Survive
And Reproduce Most (Descent with
Modification)
Evolution by Natural Selection
(Darwin)
Evidence of Evolution
How to Determine the Relatedness
of Organisms
1) Homologous Structures
• have same anatomy, may not do the same
job
• indicate common ancestor
• good measure of relatedness
2) Analogous Structures
• Do not have same anatomy, but do the same
job
• Give no evidence of a recent common
ancestor
• Not a good measure of relatedness
3) Vestigial Structures
•
•
•
structures inherited from ancestors
reduced in size
may no longer be used
Section 10.4 – Origin of Species
1) Speciation:
a) is the evolution of one species from another
b) usually occurs when species get separated from one
another for long periods of time (They DIVERGE)
c) members can no longer breed together = they have now
become separate species
d) process can also be called DIVERGENT EVOLUTION
Two Speeds of Evolution
c) Example: polar bears are related to brown bears,
but are adapted for living on ice floes, not land
Brown Bear Color Variations
Brown Bear Color Variations
Brown Bear Color Variations
Brown Bear Color Variation
Brown Bear Color Variation
3. Adaptive Radiation
a) a type of divergent evolution
b) MANY species come from a single ancestor
c) for example, Darwin’s finches
All came from a common ancestor on mainland
South America
Each island now
has its own
finch, each with
a beak adapted
for doing a
certain job =
divergent
evolution