5. Natural Selection in Action

Question 1

Give an example of natural selection in action.

Answer 1

beaks of finches on daphne major - a small island in the Galapogas archipelago

Question 2

What is the name of the species of finch in this example of natural selection in action?

Answer 2

medium ground finch (Geospiza fortis)

Question 3

What does the Geospiza fortis (medium ground finch) feed on?

Answer 3

seeds with a wide range of sizes, from small to large

Question 4

Geospiza fortis (medium ground finch) feed on seeds. What is true of the larger seeds relative to the smaller seeds? What effect has this had on the finches?

Answer 4

• larger seeds are harder and therefore more difficult to crack than the smaller seeds
• there is variation in the size of beak, some have larger beaks than others

Question 5

Is beak size a heritable characteristic?

Answer 5

yes

Question 6

How come the variation in beak size can be measured?

Answer 6

finches have been ‘trapped’ (too small to fly over windy ocean) on the island since 1973

Question 7

What sort of variations in beak have been measured?

Answer 7

• variation in width

- variation in length

Question 8

Describe the climate of the Galapagos archipelago. Why is it like this?

Answer 8

very variable - oscillation between:

• warm ocean temperatures (El Nino) = heavy rain
• cold ocean temperatures (El Nina) = droughts

Question 9

What sort of seeds are available in droughts?

Answer 9

• mostly large seeds, less small soft seeds

Question 10

What sort of weather conditions did the Galapagos archipelago experience between 1974 and 1977? What was the effect of these conditions?

Answer 10

• La nina conditions, ending with a severe drought

- G. fortis (finches) population dropping from 1,300 to 300

Question 11

During 1974 - 1977, what was the mean beak size of the finches? Explain how this happened.

Answer 11

‘large’ relative to the years before:

• 1974-1977 = El Nina conditions = drought
• in drought, there are fewer small soft seeds, and more big hard seeds
• ‘larger’ beaked birds can crack big hard seeds better, so they are LESS likely to die
• this natural selection lead to an INCREASE in the mean beak size because ‘larger’ beaked finches were better adapted to their environment

Question 12

What happened to the mean beak size of the finch population on Daphne Island in the Galapagos archipelago after the 1974-1977 drought ended? Why?

Answer 12

the mean beak size after the drought remained roughly the same (quite large) because the offspring inherited the larger beak size from their survivor parents

Question 13

In 1983 there was a strong El Nino event. What would the effect of such an event be on the mean beak size of the G. fortis population? Explain.

Answer 13

• El Nino = heavy rain
• heavy rain = more small soft seeds
• mean beak size would therefore decrease, because finches with smaller beaks are better adapted to feeding on small seeds

Question 14

What is the role of antibiotics when given to humans?

Answer 14

to control diseases caused by bacteria in humans

Question 15

What is becoming increasingly common when trying to treat disease with antibiotics?

Answer 15

disease-causing (pathogenic) bacteria are becoming increasingly resistant to antibiotics

Question 16

What are pathogenic bacteria?

Answer 16

disease-causing bacteria

Question 17

How does the theory of evolution explain the development of antibiotic resistance in bacteria?

Answer 17

• genes that give resistance to an antibiotic occur in the microorganisms that naturally make the antibiotic
• antibiotic resistance genes can be transferred to a bacterium by means of a plasmid or in some other way. There is then variation in this type of bacterium - some are resistant, some are not.
• if doctors or vets use the antibiotic to control the bacteria it will kill bacteria that are susceptible to the antibiotic, but not those that are resistant. This is an example of natural selection (even though it is caused by humans).
• antibiotic-resistant bacteria reproduce and pass on the resistance gene to their offspring. These bacteria spread from person to person by cross-infection
• the more an antibiotic is used, the more bacteria resistant to it there will be and the fewer that are non-resistant. Excessive antibiotic use may eventually result in most bacteria being resistant.

Question 18

What could excessive use of a particular antibiotic eventually result in?

Answer 18

bacteria will become resistance