H. TYPES OF SELECTION frequency of individuals in the population with a trait range for the trait mean value for the trait in all populations, individuals are born in which there is a range in the size of a trait

if there was no selection, the population would become more and more varied over time in theory, you could have a population in which both an elephant and a weasel were just two extremes of the same species this does not normally happen, due to selection for specific traits in a population

1. Stabilizing Selection this is the most common form of selection in which the extreme values for a trait are selected against over time the mean of the populations remains the same, but the range is reduced

2. Directional Selection selection favours one of the extremes over time the population mean shifts up or down and the range generally deceases a bit

3. Disruptive Selection selection favours both of the extremes in a population the result is two populations each with an altered mean and a reduced range

4. Sexual Selection Human Beauty The influence of averaging The influence of hormones

blend of 2blend of 4blend 8 blend of 16blend of 32

low testosterone normal testosterone high testosterone

Influence of female hormones on attractiveness. Which composite of the same 10 women looks more attractive? high estrogenlow estrogen

Normal pictures of two people Facial symmetry

Two sides of the face combined to make a whole face

Two left sides or two right sides  different face

Some of the benefits to attractive looking people are: -their partners tend to be more attractive;

-they are thought to be more intelligent and sociable by their teachers who tend to give them better grades in school;

-the courts tend to treat them more leniently.

Good looks were a sign of being healthy and relatively disease free.

Research shows that even three month old babies stare at photos of the faces of attractive people longer than at photos of unattractive people.

Tallness in men is attractive-it suggests dominance, status, and power and therefore the possibility of resources.

Those faces considered to be the most beautiful are typically those which have the greatest number of facial features average to any particular culture/race. It is thought that the typically average is attractive because this suggests something which has adapted to its environment and is healthy.

SELECTION by the FEMALE # 8 –10 work on these questions now

In many species, the female selects a mate based on characteristics that she perceives will help her offspring. In each of the situations below, the female selects the ‘b’ male. EXPLAIN why she does so in each case. 8. Peacocks: a] the male has a short tail, is not brightly coloured and flies well, hiding from or avoiding most predators b] the male has a long tail, colourful body and flies poorly, getting chased by more predators and having a high fatality rate male ‘b’must be tough to survive with long tail must eat well to get minerals for bright pigments

9. Cheetah a] The male stays with the female and attempts to help raise the young b] The male impregnates the female and then immediately moves away male ‘b’ by leaving, he removes competition for food with female Cheetahs do not generally hunt cooperatively, so no advantage if he stays

10. Squirrels a] The male spends some time keeping a small area free from competitors and eats quite well, keeping itself vigorous b] The male spends all its time keeping a very large area free from competitors and eats poorly, letting itself get run down male ‘b’ ensures maximum resources for female & offspring if he dies, she can mate with someone else next time! the key is that the maximum number of her offspring survive

So why do human males and females have the secondary sexual traits that they do? List 5 or 6 secondary sexual traits (post puberty) of males and 5 or 6 of females Then for each trait, list the evolutionary advantage of that trait

What should a female look for in a male? Someone that is symmetric of face [healthy] Someone who is large & strong to able to ‘defend’ his mate & offspring It would be good if they were ‘nice’ to her, but this is not essential if he has the other traits This is where muscular, high testosterone, etc fit in Someone who looks ‘similar’ to their father as he was able to produce her

What should a male look for in a female? Someone that is symmetric of face [healthy] Someone who has wide hips & good fat stores to nurture babies If he feels that she is not ‘nice’ to him, he may go elsewhere as his loyalty is not essential here [This is where ‘curvy’, high estrogen fit in] Someone who looks ‘similar’ to their mother as she was able to produce him