1. Evolution & Sexual Selection
Pages PHG text book

2. Success Criteria How will I know if I am learning?
By the end of the lesson…
You will be able to define the terms Natural & Sexual Selection.
You will be able to explain the terms in connection with relationships.
You will be able to apply these terms to explain human mating strategies.

3. An introduction to evolution
Darwin’s Idea of natural selection is that animals will end up with physical and behavioural characteristics that allow them to perform well in competition with their rivals
Behaviour must be ADAPTIVE.
Successful helps an animal to survive and produce young that are also ‘fit’ enough to survive and reproduce. This ensures that the individuals genes are carried on to future generations.
Natural Selection = Survival of the fittest…

4. ACTIVITY – Get into groups and choose one of the following animals
ACTIVITY – Get into groups and choose one of the following animals. Spend 2 minutes deciding what characteristics in that species might be naturally selected…
Eg - Penguins = thick layer of fat to keep them warm, ability to survive in cold, ability to swim fast, clever at catching food
Crocodile Gorilla
Lion Grizzly Bear
Tiger Pigeon
Elephant Owl
Snake Giraffe
Natural selection

5. Evolution
Each living thing (organism) has a set of characteristics encoded by its genes
The organism inherits its genes from its parent(s)
Variations between organisms are caused by variations in the genotype

6. Survival of the fittest !
Evolution!
Characteristics evolve because they have been passed from one generation to the next via the genes
This requires the organism:
To live to reproductive age
To mate successfully
To ensure the offspring’s survival
Survival of the fittest !

7. Socio-biology
Socio-biology is a field of psychology which aims to explain social behaviour in evolutionary terms
A behaviour is said to be adaptive if it leads to increased survival and reproduction of an organism.
This means that the gene which causes this successful behaviour will be passed on to the next generation.
It is argued that most behaviour is adaptive, otherwise the organism would not have lived long enough to pass the genes on.
Men and women should seek out partners who are likely to produce healthy children.

8. To Start…
What What do these pictures have in common?

9. What’s the difference between Natural selection & Sexual Selection?
Key Term ALERT!!!
What’s the difference between Natural selection & Sexual Selection?

10. Natural & Sexual Selection
Natural selection =survival of the fittest
Ability to survive in a particular environment (fitness)
Sexual selection = survival of the sexiest!
Ability to attract/find a mate and reproduce successfully
These are separate processes – the characteristics that facilitate reproduction do not necessarily increase survival chances

11. Tail feathers not so good for a quick escape!

12. What is Sexual Selection?
SS = the processes through which men & women attempt to maximise their chances of reproductive success
reproduction is more important than survival
Even though they don’t necessarily aid our survival
In doing this, we consider what we need from the opposite sex to do this and therefore also what we want from the opposite sex…
TWO key processes are involved
INTRASEXUAL selection = mate competition
INTERSEXUAL selection = mate choice

13. Sexual or Natural Selection?

14. Sexual Dimorphism
In many species, males have characteristics (e.g. brighter colouration, exaggerated tails) that serve to attract females
Suggests that males are competing for the attention of females
Suggests that, in many species, females do the choosing

15. Inter-Sexual Selection
The preferences of one sex (usually females) for members of the opposite sex who possess certain qualities.
Humans are ‘pre-programmed’ to attend to displays of these important indicators and mate with the individuals who possess them.
if females prefer tall males – over time, the number of tall males will increase

16. Intersexual selection linked to Anisogamy
Female produces few, relatively large eggs, each one representing a sizable investment
Natural selection favours behaviours maximising the chances of each potential reproduction being successful, e.g. High parental investment and monogamy
Females choose the best male from those available
She is looking for the best genes offering the best chances of survival for her offspring

17. Intra-Sexual Selection
Usually males compete with each other for ‘access’ to members of the opposite sex – victors mate and pass on their genes – winning traits are passed on to the next generation.

18. INTRASEXUAl selection linked to anisogamy
Males produce a lot of small, highly mobile sperm and can fertilise many females at little cost to reproductive potential.
Cannot be sure of paternity, so natural selection favours male behaviours maximising the number of potential pregnancies.
This results in intrasexual competition between men and polygamy.
Males seek partners who display signs of fertility, i.e.youth, child bearing hips, narrow waist etc.

19. Intersexual Selection: Mate Choice
Think about it
Intersexual Selection: Mate Choice
What characteristics would indicate good resources?
Economic & financial security, good job, well educated, interpersonal skills, status, etc.
Good health, so skin, hair, weight, facial symmetry, BUT also traits that are disadvantaged (think about the peacock’s tail)
What characteristics would indicate good genes?
What characteristics would indicate good parents?
Good social skills, so caring, affectionate, strong, protective, ability to provide, nurture, etc.

20. Extension Activity Watch these clips
Have you read pages in PHG? Have you clicked a few boxes?