Transcript We saw the evidence… but HOW does evolution happen?

Evolution and Natural
Selection
Theories Explaining Evolution
Lamarck
Darwin
Organisms seem suited for their jobs and
environments
• Adaptation- a characteristic that helps
an organism survive.
Identify the Adaptations!
Lamarck’s Theory
Organisms acquire (develop) adaptations to
meet their needs in an environment.
Specifically, an organism can change its
physical traits by using its body in certain ways.
The characteristics that an organism acquires
during its life are then passed on to offspring.
Lamarck’s
theory
Crab exercises his
claw to make it
grow larger
Crab passes on the
acquired trait to
offspring
•
Narrate this picture!
Giraffe Evolution According to Lamarck
Why was Lamarck Wrong?
1. Acquired traits are not inherited
(Only traits in DNA are inherited)
?
Why was Lamarck Wrong?
2. Organisms do not evolve
X
Darwins Theory: Natural Selection
Organisms born with the best adaptations
survive and pass on their traits to offspring.
Organisms without these adaptations die
and do not reproduce. Overtime, the
population changes as more organisms
inherit the adaptation.
Darwin’s Theory- Natural Selection
Crab is born with
A slightly larger
claw.
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Crab is born with
A slightly larger
claw.
X
X
X
X
Crab is born with
a slightly larger
claw.
Crab with largest
claw survives best
and reproduces
most.
X
X
X
X
X
X
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X
Crab is born with
a slightly larger
claw.
Claw helps crab
survive and
reproduce
X
X
X
X
X
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X
X
Crab is born with
a slightly larger
claw.
Claw helps crab
survive and
reproduce
Eventually, all crabs
have the adaptation
-the population
evolved.
One day a crab is born with an even
larger claw….
One day a crab is born with an even
larger claw….
…Natural selection will continue and
the population evolves further
•
Giraffe Evolution According to Darwin
?
If you don’t know this word by now
you NEED to!
Natural Selection- survival of the
fittest
Factors that affect Natural Selection
1.
2.
3.
Factors that affect Natural Selection
1. Environmental Change
Environmental Change
Example: A population of giraffes feeds on leaves of
small bushes on the ground and short trees.
Suddenly, their environment changes! After a
drought, all of the bushes on the ground die. The
giraffes are left with only taller trees to eat from.
Though some giraffes have necks that can reach
those leaves, others do not.
Environmental Change
Brainstorm: How does environmental change affect
natural selection?
(Does a changing environment increase or decrease the
chance of natural selection happening? WHY?)
X
Factors that affect Natural Selection
1. Environmental Change
2. Competition
Competition
Example: A population of birds uses their beaks to dig
into the soil and find worms to eat. The birds have a
variety of beak sizes, but since there was always an
abundant supply of worms all of the birds were able t
feed. One spring the worm population decreased
dramatically due to a disease and the birds had to
compete over the worms. The birds with the longest
beaks were able to dig deepest into the soil and find
enough worms to survive.
Competition
Brainstorm: How does competition affect natural
selection?
(Does competition increase or decrease the chance of
natural selection happening? WHY?)
Factors that affect Natural Selection
1. Environmental Change
2. Competition
3. Variation-
Factors that affect Natural Selection
1. Environmental Change
2. Competition
3. Variation- differences in traits
Variation
In the previous two examples, the populations of
giraffes and birds had inherent variation- the giraffes
had different sized necks and the birds had different
types of beaks. What would have happened if all of
the giraffes had identical short necks? What would
have happened if the birds all had identical small
beaks? Would the populations have evolved?
VS.
Variation
What would have happened if all of the giraffes had
identical short necks? What would have happened if
the birds all had identical small beaks? Would the
populations have evolved?
VS.
3. A student noticed that male peacocks have
very beautiful and elaborate feathers while
female peacocks were rather plain. He
hypothesized that once all peacocks may have
been rather plain but the males with the more
attractive feathers were able to reproduce the
most and created offspring that also had
elaborate feathers. Over time, there were
fewer and fewer plain males as they were more
likely to die without reproducing.
Do you think the student’s theory of peacock evolution is
Darwinian or Lamarckian? Explain your reasoning.
Variation
Natural Selection
No Variation
VS.
Variation
Natural Selection
No Variation
Extinction
VS.
Partner Practice
A farmer often sprays a certain kind of insecticide, a chemical
that kills insects, on his plants to prevent locust bugs from
eating all of his corn crops. One day there was a random
change in the sequence of DNA in an a locust egg cell.
When the egg cell hatched, the locust was resistant to the
insecticide (it would not be killed by it). Since that locust
could survive and reproduce, natural selection occurred
until the entire population evolved to become resistant.
A) Identify the variation that existed in the insect
population _____________________
B) Identify the process that created this variation
_________________________
TRUE OR FALSE- Write a T next to statements that are
true according to Darwin’s Theory of Natural Selection.
Write an F next to statements that are false, or that
describe Lamarckian evolution.
____ Evolution occurs when organisms adapt to meet
their needs in an environment
____ Whole populations, not individual organisms, evolve
over time based on their environment
____ Adaptations are inherited
____ Adaptations are acquired based on use
____ If an organism is not well adapted to its
environment, it dies
____ If an organism struggles in an environment it adapts