NUMERACY IN ANIMALS
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Prime among
basic numerical faculties is the ability to distinguish between a larger
and a smaller number, says psychologist Elizabeth Brannon. Humans can do
this with ease – providing the ratio is big enough – but do other animals
share this ability? In one experiment, rhesus monkeys and university
students examined two sets of geometrical objects that appeared briefly on
a computer monitor. They had to decide which set contained more objects.
Both groups performed successfully but, importantly, Brannon’s team found
that monkeys, like humans, make more errors when two sets of objects are
close in number. The students’ performance ends up looking just like a
monkey’s. It’s practically identical,’ she says.
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Humans and monkeys are
mammals, in the animal family known as primates. These are not the only
animals whose numerical capacities rely on ratio, however. The same seems
to apply to some amphibians. Psychologist Claudia Uller’s team tempted
salamanders with two sets of fruit flies held in clear tubes. In a series
of trials, the researchers noted which tube the salamanders scampered
towards, reasoning that if they had a capacity to recognise number, they
would head for the larger number. The salamanders successfully
discriminated between tubes containing 8 and 16 flies respectively, but not
between 3 and 4, 4 and 6, or 8 and 12. So it seems that for the salamanders
to discriminate between two numbers, the larger must be at least twice as
big as the smaller. However, they could differentiate between 2 and 3 flies
just as well as between 1 and 2 flies, suggesting they recognise small
numbers in a different way from larger numbers.
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Further
support for this theory comes from studies of mosquitofish, which
instinctively join the biggest shoal* they can. A team at the University of
Padova found that while mosquitofish can tell the difference between a
group containing 3 shoal-mates and a group containing 4, they did not show
a preference between groups of 4 and 5. The team also found that
mosquitofish can discriminate between numbers up to 16, but only if the
ratio between the fish in each shoal was greater than 2:1. This indicates
that the fish, like salamanders, possess both the approximate and precise
number systems found in more intelligent animals such as infant humans and
other primates.
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While these findings are
highly suggestive, some critics argue that the animals might be relying on
other factors to complete the tasks, without considering the number itself.
‘Any study that’s claiming an animal is capable of representing number
should also be controlling for other factors,’ says Brannon. Experiments
have confirmed that primates can indeed perform numerical feats without
extra clues, but what about the more primitive animals?
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To consider
this possibility, the mosquitofish tests were repeated, this time using
varying geometrical shapes in place of fish. The team arranged these shapes
so that they had the same overall surface area and luminance even though
they contained a different number of objects. Across hundreds of trials on
14 different fish, the team found they consistently discriminated 2 objects
from 3. The team is now testing whether mosquitofish can also distinguish 3
geometric objects from 4.
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Even more primitive organisms
may share this ability. Entomologist Jurgen Tautz sent a group of bees down
a corridor, at the end of which lay two chambers – one which contained
sugar water, which they like, while the other was empty. To test the bees’
numeracy, the team marked each chamber with a different number of
geometrical shapes – between 2 and 6. The bees quickly learned to match the
number of shapes with the correct chamber. Like the salamanders and fish,
there was a limit to the bees’ mathematical prowess – they could
differentiate up to 4 shapes, but failed with 5 or 6 shapes.
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These studies
still do not show whether animals learn to count through training, or
whether they are born with the skills already intact. If the latter is
true, it would suggest there was a strong evolutionary advantage to a
mathematical mind. Proof that this may be the case has emerged from an
experiment testing the mathematical ability of three- and four-day-old
chicks. Like mosquitofish, chicks prefer to be around as many of their
siblings as possible, so they will always head towards a larger number of
their kin. If chicks spend their first few days surrounded by certain
objects, they become attached to these objects as if they were family.
Researchers placed each chick in the middle of a platform and showed it two
groups of balls of paper. Next, they hid the two piles behind screens,
changed the quantities and revealed them to the chick. This forced the
chick to perform simple computations to decide which side now contained the
biggest number of its “brothers”. Without any prior coaching, the chicks
scuttled to the larger quantity at a rate well above chance. They were
doing some very simple arithmetic, claim the researchers.
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Why these skills evolved is
not hard to imagine, since it would help almost any animal forage for food.
Animals on the prowl for sustenance must constantly decide which tree has
the most fruit, or which patch of flowers will contain the most nectar.
There are also other, less obvious, advantages of numeracy. In one
compelling example, researchers in America found that female coots appear
to calculate how many eggs they have laid – and add any in the nest laid by
an intruder – before making any decisions about adding to them. Exactly how
ancient these skills are is difficult to determine, however. Only by
studying the numerical abilities of more and more creatures using
standardised procedures can we hope to understand the basic preconditions
for the evolution of number.
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Questions 15-21
Complete the table below.
Choose NO MORE THAN THREE WORDS from
the passage for each answer. Write your answers in boxes 15-21 on your answer
sheet.
Animal
Numeracy
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Subjects
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Experiments
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Results
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Mammals and
Birds
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rhesus monkeys and humans
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looked at two sets of
geometrical objects on computer screen
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performance of two groups is
almost 15) …….
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chicks
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chose between two sets of 16)
……which are altered
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chicks can do calculations in
order to choose larger group
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coots
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the behaviour of female birds
was observed
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bird seems to have the ability
to 17) __________ eggs
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Amphibians,
fish and insects
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salamanders
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offered clear tubes containing
different quantities of 18) ………..
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salamanders distinguish
between numbers over four if bigger number is at least two times larger
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19) ……………
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shown real shoals and later
artificial ones of geometrical shapes; these are used to check the
influence of total 20) ….. and brightness
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subjects know difference
between two and three and possibly three and four, but not between four and
five
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bees
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had to learn where 21)….. was
stored
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could soon choose correct
place
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Questions 22-27
Do the following statements agree with
the information given in Reading Passage 2?
In boxes 22-27 on your answer sheet,
write
TRUE
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if the statement agrees with the information
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FALSE
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if the
statement contradicts the information
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NOT GIVEN
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if there is no information on
this
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22
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Primates are better at identifying the larger of two numbers if one
is much bigger than the other.
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23
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Jurgen Tautz trained the insects in his experiment to recognise the
shapes of individual numbers.
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24
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The
research involving young chicks took place over two separate days.
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25
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The experiment with chicks suggests that some numerical ability
exists in newborn animals.
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26
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Researchers
have experimented by altering quantities of nectar or fruit available to
certain wild animals.
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27
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When assessing the number of eggs in their nest, coots take into
account those of other birds.
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