Causes of Evolution

Ruedi Nager

Campbell et al. Chapter 23

William PaleyWilliam PaleyDESIGNDESIGN

Darwin & WallaceDarwin & WallaceEVOLUTIONEVOLUTION

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1.1 x 1030 possibilities = 3.6 x 1022 years

• How do we recognise evolution?

• What causes evolution?

• Does evolution lead to perfection?

What is evolution?

Decent with modification

What is evolution?

We can redefine evolution as a change over time

Trait value

Time t Time t+x

Low High

• How do we recognise evolution?

• What causes evolution?

• Does evolution lead to perfection?

Causes of Evolution

There are 5 causes ‘The accidental toolkit’:

• Natural selection• Genetic drift• Mutation• Gene flow• Nonrandom mating

Causes of Evolution

1. Natural Selection

There are 3 important points:

• Variation

• Differential success

Causes of Evolution

1. Natural Selection

There are 3 important points:

• Variation

• Differential success

• Inheritance

Over time there will be mainly white individuals

Causes of Evolution

1. Natural Selection

Fitness

Differences in reproductive success

- relative contribution to the next generation • survival • access to mates • breeding success

Causes of Evolution

1. Natural SelectionExample: the peppered moth

Coloration is a camouflage:

Causes of Evolution

1. Natural SelectionExample of the industrial melanism of the peppered moth

% b

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1800 1900 2000

Causes of Evolution

2. Genetic DriftRandom changes in the frequency of traits to chance factors

Occurs under 2 conditions: founder effect bottleneck effect

Causes of Evolution

2. Genetic Drift

Founder effect - when a new population is a small sample of a large population

King George III

Example: Porphyria

1 / 80,000

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Causes of Evolution

2. Genetic Drift

Bottleneck effect - when only a small fraction of the population survives that is no longer representative

Example: Lions living in the Ngorogoro

1960 1975 1990

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Causes of Evolution

2. Genetic Drift

Bottleneck effect - when only a small fraction of the population survives that is no longer representative

Example: Lions living in the Ngorogoro

1960 1975 1990

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COMMON

Causes of Evolution

3. Mutation

Changes in an organism’s DNA

Hopeful monsters

Probably of little importance

Causes of Evolution

4. Gene Flow

Changes due to movement from one place to another

20% RED

+ 2 REDS 27% RED

Causes of Evolution

5. Nonrandom Mating

Individuals with particular traits are more likely to mateSexual Selection

Boys fight Boys look fetching

Causes of Evolution

5. Nonrandom Mating

Boys fight - inter-sexual competition

The winner will mate

Causes of Evolution

5. Nonrandom Mating

Boys look fetching - intra-sexual competition

The male with the best ornament will be chosen

• How do we recognise evolution?

• What causes evolution?

• Does evolution lead to perfection?

Does Evolution lead to Perfection

Does the ability to perform improve? - ADAPTATION

Just-so-stories

The elephant’s child

Does Evolution lead to Perfection

How do we know there is an ADAPTATION?

Adaptation happens only by selection, all other changes are like a lottery

Bill size

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Does Evolution lead to Perfection

The course of evolution depends on:

• Historical constraints

• Existing variation

• Compromise

• ‘Accidental toolkit’

The Tale of the Monkey

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The Tale of the Monkey

Natural Selection Edits Variation

Variation is the fuel of evolution- next

Evolution is not the work of a designer, but the work of a tinkerer.