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W h a t i s E v o l u t i o n ?. EVOLUTION: . the process of change over time idea that new species develop from earlier species by accumulated changes “descent with modification”. Evolution is NOT…. It is NOT a fact ...it's a theory :

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  • the process of change over time
  • idea that new species develop from earlier species by accumulated changes
  • “descent with modification”.
evolution is not
Evolution is NOT…

It is NOT a fact...it's a theory:

  • Remember: a theory is a well supported testable explanation of something that occurred in the natural world.
lamarck s hypothesis inheritance of acquired characteristics
Lamarck's Hypothesis:Inheritance of Acquired Characteristics

1. “Acquired Characteristics”: Through use and/or non-use, features needed for survival are developed in each individual

2. Inheritance:“acquired characteristics”

passed on to offspring, who can continue that development.

3. New Species: enough differences have developed that new species arrise.

darwin s hypothesis natural selection
Darwin's Hypothesis:Natural Selection
  • Overproduction: more offspring produced than will survive and reproduce

2. “Survival of the fittest” (not necessarily the strongest): more adaptive traits = more survival; more offspring

    • “naturally selected”.
quick comparison
Quick Comparison

1.Environment changes thus creating a “need” to change.

1.Variations of inheritable

features which already normally exist.

2. Development of new features,

“in order to survive.” or “so that

one can survive.”

2.Environment “screens out”

(or SELECTS) features contributing

to survival, and tends to eliminate

the others

3. Those with traits which help survive and have more offspring, who inherit those traits.

3.Newly acquired traits somehow

get passed down to offspring.

4.New species form,


4.New species form,


natural selection is based on 4 facts
Natural selection is based on 4 facts:

1.Organisms produce more offspring than can survive.

2.There is variation among offspring.

3.There are limited resources

(not enough food, water, space,

etc. for everyone).

4.The organisms best fit to their environment will survive and the others will not.

organisms produce more offspring than can survive
Organisms produce more offspring than can survive.
  • Example: A frog can lay 200 eggs, yet not all eggs will survive to become adult frogs.
evidence of evolution fossils
Evidence of Evolution -- Fossils!!
  • Fossils - preserved remnants or impressions left by an organism that lived in the past.
  • Usually: deeper fossil = older
evidence of evolution embryology
Evidence of Evolution -- Embryology!
  • believed that all vertebrates evolved from common ancestor. The genetic information that guides their development is nearly the same.
  • That's why scientists can learn about human development by studying other organisms--including zebrafish.
evidence of evolution anatomical physiological similarities
Evidence of Evolution --Anatomical/Physiological Similarities
  • Notice how there are similar bones and similar structures (homologous structures) in humans, birds and whales!
    • Can you tell which is the bird and which is the whale?
divergent evolution
Divergent Evolution
  • formation of two new species from common ancestor. (The two species are said to have diverged from the same ancestor.)

aka. Adaptive Radiation


Figure 21.2a

Divergent Evolution

Structural homology


Radius and ulna










convergent evolution
Convergent Evolution
  • different groups evolve similarly because live in same environment (analagous structures)

Sticky tongue

Not a lot of teeth

Rugged stomach

Big salivary glands

adaptations inherited characteristic increase chance of survival
Adaptations!Inherited characteristic increase chance of survival
  • Why are most animals in the arctic white?
    • So they blend in with the snow and avoid being seen!
  • Why do sharks have such sharp


    • It allows them to catch their prey!
  • Why do elephants have such big ears?
    • To let heat escape their bodies so they can
    • stay cool!
results of evolution speciation
Results of Evolution -- Speciation!!
  • Speciation process that creates new species!
  • A species is a group of organisms that can naturally interbreed and produce fertile offspring.
  • The Liger--the offspring of a tiger and a lion.
  • Tigers and lions are still considered separate species, because although they can produce

offspring, the offspring

is not fertile.



  • Involves the creation of a population of organisms that are unique enough to be classified in their own group. 
  • 2 processes by which this can occur:
  • Anagenesis is the accumulation of heritable traits in a population, that transforms that population into a new species.
  • Cladogenesis is branching evolution, in which a new species arises as a branch from the evolutionary tree.  The original species still exists.  This process is the source of biological diversity.

Modes of Speciation

1.  Allopatric speciation

- geographically separate ranges; gene flow interrupted and new species evolve

2.  Sympatric speciation

- geographically overlapping populations; chromosomal changes and nonrandom mating reduce gene flow.

Remember: Species arise when individuals in a population become isolated one from the other.


Polar Bear and Grizzly Bears territories are overlapping (due to global warming) causing these 2 species to mate and produce offspring who can reproduce.

how are species reproductively isolated
How are species reproductively isolated?
  • Prezygotic barriers
      • barriers that prevent mating
  • Postzygotic barriers
      • barriers that operate after mating occurs

Prezygotic barriers

1.  Habitat isolation - Two species live in the same area, but occupy different habitats; rarely encounter each other.


2.  Behavioral isolation - Signals that attract mates are often unique to a species.  (e.g., different species of  fireflies flash different patterns)


3.  Temporal isolation

- Two species breed at different times of the day or during different seasons. 


4.  Mechanical isolation

  • Closely related species attempt to mate, but are anatomically incompatible. 
  • (Example:  flowering plants with pollination barriers; some plants are specific with respect to the insect pollinator, often occurs with butterflies/moths)

5.  Gametic isolation   

- Gametes must recognize each other. 

(Example:  fertilization of fish eggs, chemical signals between sperm and egg allows sperm to “recognize” the correct egg)


From speciation to macroevolution:

  • How then do we get from the mechanism of speciation to evolution on a grand scale; i.e., macroevolution?
  • Two models:
  • The Gradualism model - change is gradual with accumulation of unique morphological adaptation.
  • The Punctuated Equilibrium model - rapid change occurs, with a new species “erupting” from the ancestral lineage, then staying the same thereafter.




Why is genetic variation important?



no variation

  • Extinction occurs when there are no members of a species left alive.
want a ticket
Want a ticket?
  • What do these pictures represent?
What is a vestigial structure?
  • How do vestigial structures support the theory of evolution?
  • Give an example of a vestigial structure.
How do fossils serve as evidence of evolution?
  • What can we learn about evolution by looking at amino acid sequences (DNA)?
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Ticket Out
  • Copy the table below and fill in.