Causes of Evolution:
There are five causes of evolution that we need to distinguish
1. Natural Selection
Example: Industrial Melanism of Peppered Moth
The three important points about Natural Selection:
- Variation
- Different reproductive success
- Inheritance
2. Genetic Drift
| Definition: Random changes in the frequency of traits due
to chance factors |
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Occurs in nature under two conditions
- Founder Effect
- Bottleneck Effect
Founder Effect
Occurs when a new population is a small sample of a larger population
Example: Porphyria
- Inherited metabolic disease
- Frequency of that disease
- Europe 1 in 80,000
- South Africa 1 in 8,000
Bottleneck Effect
Occurs in declining population where the surviving population is no longer
representative of the original population.
Example: Lions living in the Ngorogoro
Since the population crashed there is a high frequency of sperm abnormality
3.Mutation
| Definition: changes in an organism’s DNA |
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4.Gene Flow
| Definition: changes due to movement from one place to another
and have offspring at the new place |
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5.Nonrandom Mating
| Definition: individuals with particular traits are chosen
as mates (also called assortative pairing) |
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Adaptation
| Definition: genetically determined characteristics (behavioural,
morphological, and physiological) that improve an organism’s ability
to survive and successfully reproduce under prevailing environmental
conditions. It is the product of natural selection. |
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Example: Size at maturity in guppies
Fitness
| Definition: relative contribution to the genes passed on
to the next generation |
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Fitness components:
- 1. Survival
- 2. Number of offspring
- 3. Finding a mate
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Natural Selection
Sexual Selection
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Sexual Selection
Two types of sexual selection:
1. Intra-sexual Competition
Competing for mates
Example: Red Deer
The male that wins the fight has access to females
2. Inter-sexual Competition
Being chosen by mates
Example: Long-tailed Widowbird
The male with the longest tail is chosen by females