1. Unit 1: 1.7 Evolution - Selection
Higher Biology
Unit 1:
1.7 Evolution - Selection

2. Learning Intentions
To be able to describe how selection processes drive evolution
To be able to use numeracy skills to analyse graphs and explain what is shown

3. Success Criteria
I can give examples of selection that take place within species
I can explain how selection methods drive evolution
I can describe and explain changes in population graphs

4. Selection
Selection is the process by which the frequencies of some DNA sequences increase within a population
The sequences that increase are said to be selected for and those that decrease are selected against
This occurs in a non random manner

5. Types of selection
Continuous variables such as height, weight and seed size are controlled by many genes
They are said to be polygenic

6. Natural selection
Natural selection states that only the organisms with the characteristics best suited for their environment will survive and reproduce
The genes that control these characteristics will then be passed onto their offspring

7. Natural Selection
Organisms whose characteristics are not well suited to the environment are more likely to be predated upon or die before reaching reproductive age
The genes for the poorly suited characteristics are therefore lost
The process of natural selection occurs generation after generation and will continue to occur as the environment changes

8. Sexual Selection
Females and males have different investments in reproduction
Males produce lots of sperm and are capable of fertilising many females in a short period of time
Females spend more energy producing fewer eggs and tend to show more parental care than males
Males and females have therefore evolved strategies to try and maximise their reproductive potential

9. Sexual Selection
Sexual selection is a non random process that results in the increase in frequency of sequences of DNA that increase the reproductive success
Reproductive success can be classes as successful matings as well as number of surviving offspring

10. Male to male competition
One form of sexual selection is male to male competition
Males compete for territory and access to females
Examples include deer and elephant seals

11. Deer competition
One way male deer compete with each other for mates is by locking horns. The male who wins in this competition is the “fittest” and therefore has the strongest genes to pass on. Aggressive competition between males can result in serious injury or death, some animals have devised other ways to compete to reduce this risk.

12. Elephant seals competing for mates

13. Female choice
In some situations it is the female who makes the choice of mate
Females select a male to mate with who will give their offspring the best chance of survival
This is often based upon males performing a display for the female
Examples include the red capped manakin and peacocks

14. Peacocks
The peacock is much more brightly coloured and noticeable than the female peahen. Males attract females by displaying their bright plumage. Females select a male who has the best display and plumage.

15. Sexual selection
In both male to male competition and female choice their has been a cost in the evolution of reproductive strategies
Males have had to evolve structures to allow them to attract females
By singing and displaying male birds are putting themselves at increased risk of attracting predators

16. Red capped manakin video

17. Normal distribution
When quantitative data is collected for continuous variables in a large population we would expect to see a normal distribution that looks like a bell shaped curve

18. Normal distribution Increasing number of population
Increasing value of inherited characteristic (height, weight)

19. Natural selection can affect the distribution of characteristics within a population in 3 different ways

20. Stabilising Selection
This form of selection exerts pressure against the extreme variants of a characteristic
This leads to a reduction in genetic diversity
It operates in an unchanging environment and maintains the status quo for the best adapted organisms

22. Directional selection
Most common during a period of environmental change
Favours a version of the characteristic that was originally less common
Results in a directional change in the mean value
Examples include average size of bears increasing during each ice age

24. Disruptive Selection
Extreme forms of a characteristic are favoured instead of the intermediates
Results in a population being split into 2 distinct groups
Occurs when two different habitats or types of resource become available
Selective breeding is a form of disruptive selection

27. Success Criteria
I can give examples of selection that take place within species
I can explain how selection methods drive evolution
I can describe and explain changes in population graphs