Download Teacher notes and student sheets

AS Science In Society 1.9
Teacher Notes
Introduction
Darwin’s voyage in the Beagle from 1831 to 1836 is very well known,
as is his visit to the Galapagos Islands. This activity asks students to
read and interpret a story, which has been written to highlight how
Darwin’s observations on the Galapagos (e.g. distribution of finches)
could be explained by natural selection. This might make a good pair
or small group activity.
Resources
Textbook pp 138 - 140
Student briefing sheets
Access to internet or reference
books for timeline.
How Science Works
Answers to questions
1. Explain why it is unlikely that more than one flock
of birds would find the islands in this way at the
same time.
The island was a long way from the mainland, in
a very large ocean.
2. Suggest two possible reasons why there were no
predators on the island.
no food for them as no other birds there
they had not evolved yet, the islands were
volcanic and relatively new. Animals could not
there as easily as birds
3. Why were there no other birds to compete with?
(see Q1)
4. Why might some finches survive better than
others on the same food sources?
size or shape of beak
5. Why were the finches slightly different on each
island?
because they evolved to feed on seeds and other
food which was different on each island
November 2008
Page 1
Cc An event is often explained by relating it to a particular scientific
theory (or theories). A scientific theory proposes an underlying
process that results in the observations we have made. Many
scientific theories involve objects or properties that cannot be
directly observed. Scientific theories do not ‘emerge’ from data by a
process of logical deduction; proposing an explanation always
involves imagination and conjecture. An explanation is not just a
summary of the data, but is distinct from it.
Ce Scientists are more confident about theories that include a
plausible mechanism for causing the events observed. It is also
important that a new theory is consistent with existing theories that
are well-established and generally accepted.
Science explanations
Gb One of the mechanisms central to the explanation of evolution
is natural selection. There is usually variation between individuals
of the same species. Some have characteristics which give them a
better chance of surviving and reproducing in a particular
environment. These individuals will pass on their characteristics to
the next generation. The genes for the advantageous
characteristics will become more common as a result
Gc Natural selection leads, over many generations, to a gradual
change in the characteristics of a whole population. When the
change is great enough the population becomes a new species
that no longer interbreeds with the original species. Most biologists
think that a new species normally arises in a population that is
isolated from the original species during the evolutionary change
Ha In any given environment, or ecosystem, there is competition
between several species for the materials they require to live and
reproduce. Species may also be dependent on other species in the
ecosystem.
Hb As a result of these complex patterns of interdependence and
competition for resources changes which affect one species can
have extensive knock-on effects on other species. Some minor
disruptions lead to changes which restore the ecosystem to
stability; others can change the ecosystem permanently leading to
a new stability or in extreme cases destruction of the whole
ecosystem.
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.9
Student sheets
Introduction
Although Alfred Wallace should perhaps share the credit for the Theory of Evolution by Natural
Selection, Darwin was the one who gathered the evidence needed, made detailed records of personal
observations, and finally published the major book which presented his ideas to the scientific community.
The book Darwin published about his theory, On the Origin of Species, was based partly on observations
he made on a five year journey around the world on the ship, HMS Beagle. What exactly was the
importance of this famous journey? What other science was informing Darwin and opinions at the time?
A good scientific theory has to fit in with other ideas of the time. For example, Darwin’s theory of
evolution fitted well with knowledge and ideas in geology and populations. Later discoveries in genetics
served to deepen understanding of the theory. This made it a very strong theory indeed.
(Look at the map of Darwin’s voyage on p.138 of the textbook).
The Activity
Part of Darwin’s voyage included a visit to the Galapagos Islands in the Pacific Ocean, close to South
America. Islands form a very important piece of evidence in Darwin’s theory, because they isolate
populations from each other.
Read the story below:
A long time ago, a small flock of sparrow-like birds called finches were blown out to sea by a fierce
storm. They lost their bearings but flew on in search of the mainland, going further and further out to
sea.
At the point of exhaustion, 600 miles from home, they spotted a speck of land - an island in the
middle of the sea. They were saved and could rest, drink and feed before returning home. But this
island was perfect: it had abundant seeds and other food, plenty of shelter, nesting sites and
(amazingly) no predators or other birds to compete with. Life was much harder on the mainland.
There was no need for the birds to move on.
Their numbers grew - until they became just a bit too numerous for the little island. Some found it
hard to find enough food for themselves or their offspring, and young birds were driven away from
areas where food was available. Some birds were forced to fly across the sea to nearby islands.
There, they found new territories, also with no predators or other birds to compete with. As the plants
and their seeds were just a little different on each island, some birds were better than others at
finding and eating the new food sources. Birds which could break open fruits and eat the seeds
survived well enough to produce lots of babies. Eventually, after a very long time, all the islands
became occupied by these birds but the finches on each island were slightly different.
Page 1
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.9
Student sheets
Scientists believe that this story is just the sort of scenario that happens when new, volcanic islands like
the Galapagos are colonised by animals (and plants). It shows how a theory has to include a plausible
mechanism to explain events. The questions in this activity are similar to those which a scientist like
Darwin would have to deal with when presenting his theory to other (sceptical) scientists.
Answer the following questions about the story using Darwin’s theory and discuss your answers with a
partner or in a small group.
Discussion questions
1. Explain why it is unlikely that more than one flock of birds would find the islands in this way at the
same time.
2. Suggest two possible reasons why there were no predators on the island.
3. Why were there no other birds to compete with? (see Q1)
4. Why might some finches survive better than others on the same food sources?
5. Why were the finches slightly different on each island?
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges