1. Causes of Evolution
Ruedi Nager
Campbell et al. Chapter 23

2. William Paley
DESIGN
Darwin & Wallace
EVOLUTION

4. 1.1 x 1030 possibilities = 3.6 x 1022 years

5. How do we recognise evolution?
What causes evolution?
Does evolution lead to perfection?

6. What is evolution?
Decent with modification

7. What is evolution? We can redefine evolution as a change over time
Time t
Time t+x
Low High
Trait value
We can redefine evolution
as a change over time

8. How do we recognise evolution?
What causes evolution?
Does evolution lead to perfection?

9. Causes of Evolution There are 5 causes ‘The accidental toolkit’:
Natural selection
Genetic drift
Mutation
Gene flow
Nonrandom mating

10. Causes of Evolution 1. Natural Selection There are 3 important points:
Variation
Differential success

11. Causes of Evolution 1. Natural Selection
There are 3 important points:
Variation
Differential success
Inheritance
Over time there will be mainly white individuals

12. Causes of Evolution 1. Natural Selection
Differences in reproductive success
Fitness
- relative contribution to the next generation
• survival
• access to mates
• breeding success

13. Causes of Evolution 1. Natural Selection Example: the peppered moth
Coloration is a camouflage:

14. Causes of Evolution 1. Natural Selection
Example of the industrial melanism of the peppered moth
% black form

15. Causes of Evolution 2. Genetic Drift
Random changes in the frequency of traits to
chance factors
Occurs under 2 conditions: founder effect
bottleneck effect

16. 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
1 / 8,000

17. Causes of Evolution 2. Genetic Drift
Before crash
RARE
Bottleneck effect - when only a small fraction of the
population survives that is no longer representative
Example: Lions living in the Ngorogoro
Number of lions
100 50

18. 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
100
After crash
Number of lions 50
COMMON

19. Causes of Evolution 3. Mutation Changes in an organism’s DNA
Hopeful monsters
Probably of little importance

20. Causes of Evolution 4. Gene Flow
Changes due to movement from one place to another
20% RED
+ 2 REDS  27% RED

21. Causes of Evolution 5. Nonrandom Mating
Individuals with particular traits are more likely to mate
Sexual Selection
Boys fight
Boys look fetching

22. Causes of Evolution 5. Nonrandom Mating
Boys fight - inter-sexual competition
The winner will mate

23. Causes of Evolution 5. Nonrandom Mating
Boys look fetching - intra-sexual competition
The male with the best ornament will be chosen

24. How do we recognise evolution?
What causes evolution?
Does evolution lead to perfection?

25. Does Evolution lead to Perfection
Does the ability to perform improve? - ADAPTATION
Just-so-stories
The elephant’s child

26. Does Evolution lead to Perfection
How do we know there is an ADAPTATION?
Foraging efficiency
Bill size
Adaptation happens only by selection,
all other changes are like a lottery

27. Does Evolution lead to Perfection
Existing variation
The course of evolution depends on:
Historical constraints
Compromise
‘Accidental toolkit’

28. The Tale of the Monkey

29. The Tale of the Monkey 1 10 20
Natural Selection Edits Variation

30. Evolution is not the work of a designer, but the work of a tinkerer.
Variation is the fuel of evolution
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