Theme - Selection

Question 1

By what three methods can evolution by selection occur?

Answer 1

Natural, sexual and artificial

Question 2

What is an adaptation?

Answer 2

A trait that gives an organism a better ability to survive and reproduce in a certain environment.
Trait can be morphological, physiological, biochemical, behavioural or developmental.

Question 3

What must be present for natural selection to occur?

Answer 3

Variation of a trait within the population

Question 4

What is natural selection?

Answer 4

The differential survival of organisms in a population due to their physical attributes (phenotype)

Question 5

What three criteria must be present in a population for natural selection to occur?

Answer 5

1. Phenotypic variation
2. That is genetically derived
3. That leads to a difference in fitness (survival and/or mating success), ultimately expressed as reproductive success

Question 6

Name the three types of natural selection

Answer 6

1. Directional
2. Disruptive
3. Stabilising

Question 7

What is favoured in directional selection and what is the result?

Answer 7

One extreme of the phenotype is favoured.
As a result, the frequency of this shifts to one side.
Example: leads to increased body size in competing common toad males, as the largest win the fight and breed.

Question 8

What is acted against in stabilising selection?

Answer 8

Both extremes of the phenotype are acted against - the mid point is the optimal value for the trait

Question 9

Give an example of stabilising selection

Answer 9

Goldenrod gall flies. Lay their eggs on goldenrod plant, which turns to a gall with chemical interaction.
Large galls are visible and eaten by woodpeckers.
Small galls are parasitized by wasps.
Medium sized galls survive to reproduce.

Question 10

What happens in disruptive selection? What is the result?

Answer 10

Both extremes of the phenotype are favoured, and the mid-value trait is acted against.
This results in increased variation.

Question 11

Which types of selection can lead to speciation?

Answer 11

Directional and disruptive

Question 12

What ultimately is responsible for genetic change?

Answer 12

The differential reproduction of individuals who carry alleles underlying the trait

Question 13

Why did the ground finches evolve so quickly?

Answer 13

Drought mean that only certain foods were available. Those birds with large beaks strong enough to break seeds could eat and survive; those with smaller beaks starved.
As the trait for large beak is inherited, the next generation of birds had greater frequency of large beaks.

Question 14

What is the difference between sexual and natural selection?

Answer 14

Sexual selection acts on traits that are preferred by mates, leading to increased reproductive success. They do not help (and may even hinder) survival.

Question 15

Describe the inequality of reproductive investment between males and females.

Answer 15

Males produce many small, motile gametes (sperm).

Females produce fewer, larger eggs.

Question 16

What results from the inequal reproductive investments between males and females.

Answer 16

Females tend to care for young so are only available for some of the time.
Males are free to mate most of the time, leading to competition between males for the lower number of females.

Question 17

What are the two main strategies employed by males.

Answer 17

Physically control resources or fight other males for access to females.
Display to females in the hope they will be chosen.

Question 18

What are the consequences of fighting for access to females?

Answer 18

The largest/strongest win meaning they reproduce and pass on their genes, leading to:

• larger body size in males and sexual dimorphism between the sexes
• weaponry such as horns, teeth, mandibles

Question 19

What is intrasexual selection acting on? Give an example.

Answer 19

It acts within the sexes.

Example: evolution of weapons in fighting males.

Question 20

What is intersexual selection acting on? Give an example.

Answer 20

It acts between the sexes.

Example: female choice of male with extravagant ornament.

Question 21

Why can some traits that given a reproductive advantage (sexual selection) act against natural selection?

Answer 21

Extravagant traits such the large claw in fiddler crabs makes them more conspicuous to predators.

Question 22

Give an example of artificial selection

Answer 22

The Russian experiment carried out on red fox (Vulpes vulpes) to breed out fear and aggression of humans; many examples from domesticated animals used in farming (cows for milk vs meat)

Question 23

Apart from emphasising desired traits, what are some other outcomes of taming animals?

Answer 23

Reduced sexual dimorphism (males more feminised)
Smaller brain size
Lower levels of corticosteroids (stress hormones)
Increased ‘social intelligence’
Faster post-natal development
Delayed fear response