Download File - Mr. Shanks` Class

H. TYPES OF SELECTION
range for the trait
frequency of
individuals in
the population
with a 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 2
blend of 4
blend of 16
blend of 32
blend 8
low testosterone
normal testosterone
high testosterone
Influence of female hormones on attractiveness.
Which composite of the same 10 women looks more attractive?
high estrogen
low estrogen
Facial symmetry
Normal pictures of two people
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.
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.
1. 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
2. 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
3. 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
This is where muscular, high testosterone, etc fit in
Someone who looks ‘similar’ to their father as he
was able to produce her
It would be good if they were ‘nice’ to her, but this
is not essential if he has the other traits
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
[This is where ‘curvy’, high estrogen fit in]
Someone who looks ‘similar’ to their mother as she
was able to produce him
If he feels that she is not ‘nice’ to him, he may go
elsewhere as his loyalty is not essential here