Mechanisms of Evolution

Concept 2 – Analyzing Descent with Modification: A Darwinian

View of Life(Ch 22)

Part 2: Evidence for Evolution

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If a NEW trait is to arise and flourish in a population, what two events must occur?

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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)

The new trait must increase the fitness of individuals in their environment (to be passed on). This is natural SELECTION.

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Reminder… selection usually occurs on existing traits within the varied population!

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Define: 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.

Fitness = reproductive success

Common Misconceptions

Adaptation –

Common Misconceptions

Adaptation – NOT an individual changing over its lifetime in response to the environment.

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: Gamete formation Random fertilization

Evolution –

Natural Selection –

Evolution

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.

Evolution

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

Any Questions? Finish the handout from last class!

(Answers posted online)

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True or False? An organism mutates in order to adapt to its

environment

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True or False? An organism mutates in order to adapt to its

environment 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!

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If selection favours increased antibiotic resistance in a population of bacteria:

A. The bacteria become more resistant over time.

B. More bacteria become resistant over time.

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If direction selection favours increased antibiotic resistance in a population of bacteria:

A. The bacteria become more resistant over time.

B. More bacteria become resistant over time!

Darwin vs Lamarck

Lamarck thought that evolution worked through the inheritance of acquired characteristics...

Hmm... Let’s look at Epigenetics Daphnia (Water Flea)

Did Lamarck have a point after all?