Transcript Mechanisms of Evolution

Mechanisms of
Evolution
Concept 2 – Analyzing Descent
with Modification: A Darwinian
View of Life
(Ch 22)
Part 2: Evidence for Evolution
Try This!

If a NEW trait is to arise and flourish in a
population, what two events must occur?
Try This!

If a NEW trait is to arise and flourish in a
population, what two events must occur?

New traits appear because of random mutation
and sexual recombination. (RARE)
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The new trait must increase the fitness of
individuals in their environment (to be passed on).
This is natural SELECTION.
Try This!
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Reminder… selection usually occurs on
existing traits within the varied population!
Try This!
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Define:
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Fitness
Adaptation
Mutations
Variation
Evolution
Natural Selection
Common Misconceptions

Fitness –
Common Misconceptions

Fitness – NOT an organism’s general health,
vigor, strength, or intelligence!

Any trait that increases an organism’s relative
reproductive success increases its fitness.
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Fitness = reproductive success
Common Misconceptions

Adaptation –
Common Misconceptions

Adaptation – NOT an individual changing
over its lifetime in response to the
environment.
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IT IS: An inherited characteristic that
increased previous generation’s reproductive
success (and most likely the individual’s)
Common Misconceptions

Mutations –
Common Misconceptions

Mutations – NOT intentional events! NOT
adaptive responses to environmental
conditions!

Mutations – ARE rarely positive and random
events where the DNA code is altered.
Common Misconceptions

Variation -
Common Misconceptions

Variation – Every population exhibits natural
variation in characteristics. Variation is
maintained via shuffling of genetic alleles
during sexual reproduction during:
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Gamete formation
Random fertilization
Evolution
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Evolution –
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Natural Selection –
Evolution
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Evolution – Descent with Modification. In
other words, present species are
descendants of ancestral species.

Natural Selection –
Evolution

Evolution – Descent with Modification. In
other words, present species are
descendants of ancestral species.

Natural Selection – This is the process by
which Evolution occurs in which organisms
with certain inherited characteristics are more
likely to survive and reproduce than
organisms with other inherited
characteristics.
Concept 2:
Descent with Modification
You must know:
 How Lamarck’s view of the mechanism of
evolution differed from Darwin’s
 Several examples of evidence for evolution
 The differences between structures that are
homologous and those that are analogous, and how
this relates to evolution
 The role of adaptations, variation, time, reproductive
success, and heritability in evolution
Darwin vs Lamarck
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Any Questions?
Finish the handout from last class!
(Answers posted online)
Try This!
True or False?
 An organism mutates in order to adapt to its
environment
Try This!
True or False?
 An organism mutates in order to adapt to its
environment
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FALSE. Positive mutations are rare and random events!
An organism cannot “decide” to mutate!
Even if new traits can appear through random mutation
and sexual recombination, it must increase the fitness of
individuals in their environment the trait will be selected for.
IT IS THE POPULATION, NOT THE INDIVIDUAL, THAT
EVOLVES!
Try This!
If selection favours increased antibiotic
resistance in a population of bacteria:

A.
B.
The bacteria become more resistant over time.
More bacteria become resistant over time.
Try This!
If direction selection favours increased
antibiotic resistance in a population of
bacteria:

A.
B.
The bacteria become more resistant over time.
More bacteria become resistant over time!
Darwin vs Lamarck
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Lamarck thought that evolution worked
through the inheritance of acquired
characteristics...
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Hmm... Let’s look at Epigenetics
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Daphnia (Water Flea)
Did Lamarck have a
point after all?