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IB Biology: Evolution. Data analysis. Name:____________________
Read ALL of the information below carefully and answer the questions.
Darwin’s Finches.
Introduction:
Charles Darwin visited the Galapagos Islands on his voyage in 1831.
He tried to explain the variety and distribution of finches (small birds) on
the islands by suggesting that they had adapted to different conditions on
different islands, by natural selection.
However he could not find any hard evidence to support his ideas.
The Galapagos Islands
In the 1980’s and 90’s the scientist Peter Grant visited some of the islands over a period of about 10 years.
He collected data which did support Darwin’s theories. He made thousands of measurements of beak length,
width, and so on. This was quite easy as the birds can be easily picked up and handled.
Most islands are uninhabited and there are no humans or predators.
beak
All of the data and information below refers to the ‘Medium Ground Finch’,
Geospiza fortis’, found on the small island ‘Daphne major’.
The ‘medium ground
finch’ – Geospiza
fortis.
Impotant information:

The beak lengths of 10 birds was first measured at a time when food was plentiful;

10 different individuals were later measured at the end of a period of
drought, which had lasted about 5 years. (time for 4 generations of finches)

 The birds feed by cracking open tough seeds of Tribulus, a common plant
on the islands. All birds can open smaller seeds. Only birds with longer beaks can
open the large tougher seeds, but this takes a bit more energy than a small seed.

Reproduction and growth in the Tribulus is seriously reduced by lack of water during a drought.
Tribulus seed
Lengths of beaks ‘Geospiza’ birds before a drought, and (different birds) at the end of a drought.
Lengths before
Lengths at end of a
drought / mm
drought / mm
10
12
9
15
12
12
9
10
11
13
11
12
10
11
11
12
12
11
11
12
Mean
length/mm
Q1.
10.5
Using graph paper provided, display the data in the most appropriate form.
You can use two separate axes, or put both sets on one axis.
(5)
Answer questions 2 to 7 in the spaces on this page.
g10 evolution data question. Geospiza
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IB Biology: Evolution. Data analysis. Name:____________________
2.
Calculate the mean (average) beak length after the drought. Show your working.
(2)
Answer: ___________
4.
Describe one similarity between the two groups of birds shown by the data.
(2)
5.
Other than the mean values, describe one difference between the two groups of birds that is shown
by the data or the chart.
(2)
6.
Suggest how the change in the mean beak length over the 5 years helps the birds survive?
7.
The birds could be said to ‘become adapted’ to the drought. What actually becomes adapted?
(a) a single bird with (the right) advantageous features
(b) a population of birds of the same species which all have advantageous features?
(c) A population of birds of the same species, a few of which have advantageous features
(d) A single bird which needed to change to survive.
Answer (answer a, b, c or d) ________
(1)
(2)
Answer on lined paper: (You are recommended to write BULLET POINTS.)
8.
Describe how Darwin might have explained the change in the beaks during the years of drought.
You must use the correct vocabulary to gain full marks.
(10)
9.
Explain how natural selection could still happen in a group of these finches over a 20 year period
when there was regular rainfall and good plant growth, and conditions were not changing.
(2)
(Total: 30)
Vocabulary: Drought – lack of rainfall and fresh water. Uninhabited = nobody lives there.
g10 evolution data question. Geospiza
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30/4/17 mjs