The sequence, in which each number is the sum of the two preceding numbers is known as the Fibonacci series:
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610,
987, 1597, 2584, 4181, ... (each number is the sum of the
previous two).
The ratio of successive pairs tends to the so-called golden section
(GS) - 1.618033989 . . . . . whose reciprocal is 0.618033989 . . . . . so that we have 1/GS = 1 + GS.
The Fibonacci sequence, generated by the rule f1 = f2 = 1 , fn+1 = fn + fn-1,
is well known in many different areas of mathematics and science.
However, it is quite amazing that the Fibonacci number
patterns occur so frequently in nature ( flowers, shells,
plants, leaves, to name a few) that this phenomenon appears
to be one of the principal "laws of nature".
History of Fibonacci Number
Fibonacci
was known in his time and is still recognized today as the
"greatest European mathematician of the middle ages." He was
born in the 1170's and died in the 1240's and there is now a
statue commemorating him located at the Leaning Tower end of the
cemetery next to the Cathedral in Pisa. Fibonacci's name is also
perpetuated in two streetsthe quayside Lungarno Fibonacci in
Pisa and the Via Fibonacci in Florence.
His
full name was Leonardo of Pisa, or Leonardo Pisano in Italian
since he was born in Pisa. He called himself Fibonacci which was
short for Filius Bonacci, standing for "son of Bonacci",
which was his father's name. Leonardo's father( Guglielmo Bonacci)
was a kind of customs officer in the North African town of
Bugia, now called Bougie. So Fibonacci grew up with a North
African education under the Moors and later travelled
extensively around the Mediterranean coast. He then met with
many merchants and learned of their systems of doing
arithmetic. He soon realized the many advantages of the
"Hindu-Arabic" system over all the others. He was one of the
first people to introduce the Hindu-Arabic number system
into Europe-the system we now use today- based of ten digits
with its decimal point and a symbol for zero: 1 2 3 4 5 6 7 8
9. and 0
His book on how to do arithmetic in the
decimal system, called Liber abbaci (meaning Book of the
Abacus or Book of calculating) completed in 1202 persuaded
many of the European mathematicians of his day to use his
"new" system. The book goes into detail (in Latin) with the
rules we all now learn in elementary school for adding,
subtracting, multiplying and dividing numbers altogether with many
problems to illustrate the methods in detail.
(
http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fibnat.html#Rabbits )
Pascal's Triangle and Fibonacci Numbers
The
triangle was studied by B. Pascal, although it had been
described centuries earlier by Chinese mathematician Yanghui
(about 500 years earlier, in fact) and the Persian
astronomer-poet Omar Khayyám.
Pascal's Triangle is described by the following formula:
The "shallow diagonals" of Pascal's triangle sum to Fibonacci numbers.
Fibonacci and Nature
Flower Patterns and Fibonacci Numbers
Why
is it that the number of petals in a flower is often one of
the following numbers: 3, 5, 8, 13, 21, 34 or 55? For example, the
lily has three petals, buttercups have five of them, the
chicory has 21 of them, the daisy has often 34 or 55
petals, etc. Furthermore, when one observes the heads of
sunflowers, one notices two series of curves, one winding
in one sense and one in another; the number of spirals not
being the same in each sense. Why is the number of spirals
in general either 21 and 34, either 34 and 55, either 55 and
89, or 89 and 144? The same for pinecones : why do they have either
8 spirals from one side and 13 from the other, or either 5
spirals from one side and 8 from the other? Finally, why is
the number of diagonals of a pineapple also 8 in one
direction and 13 in the other?
Passion Fruit
© All rights reserved Image Source >>
Are these numbers the product of chance? No! They all belong to the Fibonacci sequence:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144,
etc. (where each number is obtained from the sum of the
two preceding). A more abstract way of putting it is that
the Fibonacci numbers fn are given by the formula f1 = 1,
f2 = 2, f3 = 3, f4 = 5 and generally f n+2 = fn+1 + fn .
For a long time, it had been noticed that these numbers
were important in nature, but only relatively recently that
one understands why. It is a question of efficiency during the
growth process of plants.
The explanation is
linked to another famous number, the golden mean, itself
intimately linked to the spiral form of certain types of
shell. Let's mention also that in the case of the
sunflower, the
pineapple and of the pinecone, the correspondence with the
Fibonacci numbers is very exact, while in the case of the
number of flower petals, it is only verified on average
(and in certain cases, the number is doubled since the
petals are arranged on two levels).
© All rights reserved.
Let's
underline also that although Fibonacci historically
introduced these numbers in 1202 in attempting to model the growth
of populations of rabbits, this does not at all correspond to
reality! On the contrary, as we have just seen, his numbers
play really a fundamental role in the context of the growth
of plants
THE EFFECTIVENESS OF THE GOLDEN MEAN
The
explanation which follows is very succinct. For a much more
detailed explanation, with very interesting animations, see the web
site in the reference.
In
many cases, the head of a flower is made up of small seeds
which are produced at the centre, and then migrate towards the
outside to fill eventually all the space (as for the sunflower but
on a much smaller level). Each new seed appears at a certain
angle in relation to the preceeding one. For example, if
the angle is 90 degrees, that is 1/4 of a turn, the result
after several generations is that represented by figure 1.

Of course, this is not the most
efficient way of filling space. In fact, if the angle
between the appearance of each seed is a portion of a turn
which corresponds to a simple fraction, 1/3, 1/4, 3/4, 2/5,
3/7, etc (that is a simple rational number), one always
obtains a series of straight lines. If one wants to avoid this
rectilinear pattern, it is necessary to choose a portion of the
circle which is an irrational number (or a nonsimple fraction).
If this latter is well approximated by a simple fraction,
one obtains a series of curved lines (spiral arms) which
even then do not fill out the space perfectly (figure 2).
In
order to optimize the filling, it is necessary to choose the
most irrational number there is, that is to say, the one the least
well approximated by a fraction. This number is exactly the
golden mean. The corresponding angle, the golden angle, is
137.5 degrees. (It is obtained by multiplying the non-whole
part of the golden mean by 360 degrees and, since one
obtains an angle greater than 180 degrees, by taking its
complement). With this angle, one obtains the optimal
filling, that is, the same spacing between all the seeds
(figure 3).
This angle has to be
chosen very precisely: variations of 1/10 of a degree
destroy completely the optimization. (In fig 2, the angle
is 137.6 degrees!) When the angle is exactly the golden mean, and
only this one, two families of spirals (one in each direction)
are then visible: their numbers correspond to the numerator
and denominator of one of the fractions which approximates
the golden mean : 2/3, 3/5, 5/8, 8/13, 13/21, etc.
These
numbers are precisely those of the Fibonacci sequence (the
bigger the numbers, the better the approximation) and the choice of
the fraction depends on the time laps between the appearance
of each of the seeds at the center of the flower.
This is why the number of spirals in the centers of
sunflowers, and in the centers of flowers in general,
correspond to a Fibonacci number. Moreover, generally the
petals of flowers are formed at the extremity of one of the
families of spiral. This then is also why the number of
petals corresponds on average to a Fibonacci number.
REFERENCES:
-
An excellent Internet site of Ron Knot's at the University of Surrey on this and related topics.
-
S.
Douady et Y. Couder, La physique des spirales végétales,
La Recherche, janvier 1993, p. 26 (In French).
Human Hand
Every
human has two hands, each one of these has five fingers,
each finger has three parts which are separated by two knuckles. All
of these numbers fit into the sequence. However keep in mind,
this could simply be coincidence.
Human Face
Knowledge
of the golden section, ratio and rectangle goes back to the
Greeks, who based their most famous work of art on them: the
Parthenon is full of golden rectangles. The Greek followers of the
mathematician and mystic Pythagoras even thought of the golden
ratio as divine.
Later,
Leonardo da Vinci painted Mona Lisa's face to fit perfectly
into a golden rectangle, and structured the rest of the
painting around similar rectangles.
Mozart
divided a striking number of his sonatas into two parts
whose lengths reflect the golden ratio, though there is much
debate about whether he was conscious of this. In more modern
times, Hungarian composer Bela Bartok and French architect Le
Corbusier purposefully incorporated the golden ratio into their
work.
Even today, the golden ratio is in
human-made objects all around us. Look at almost any
Christian cross; the ratio of the vertical part to the
horizontal is the golden ratio. To find a golden rectangle,
you need to look no further than the credit cards in your
wallet.
Despite these numerous appearances in works
of art throughout the ages, there is an ongoing debate among
psychologists about whether people really do perceive the
golden shapes, particularly the golden rectangle, as more
beautiful than other shapes. In a 1995 article in the
journal Perception, professor Christopher Green,
of York
University in Toronto, discusses several experiments over the years
that have shown no measurable preference for the golden
rectangle, but notes that several others have provided
evidence suggesting such a preference exists.
Regardless
of the science, the golden ratio retains a mystique, partly
because excellent approximations of it turn up in many
unexpected places in nature. The spiral inside a nautilus shell is
remarkably close to the golden section, and the ratio of the
lengths of the thorax and abdomen in most bees is nearly the
golden ratio. Even a cross section of the most common form
of human DNA fits nicely into a golden decagon. The golden
ratio and its relatives also appear in many unexpected
contexts in mathematics, and they continue to spark interest
in the mathematical community.
Dr. Stephen
Marquardt, a former plastic surgeon, has used the golden
section, that enigmatic number that has long stood for
beauty, and some of its relatives to make a mask that he
claims is the most beautiful shape a human face can have.
Egyptian Queen Nefertiti (1400 B.C.)
Fibonacci's Rabbits
The
original problem that Fibonacci investigated, in the year
1202, was about how fast rabbits could breed in ideal circumstances.
"A pair of rabbits, one month old, is too young to reproduce.
Suppose that in their second month, and every month
thereafter, they produce a new pair. If each new pair of
rabbits does the same, and none of the rabbits dies, how
many pairs of rabbits will there be at the beginning of each
month?"
- At the end of the first month, they mate, but there is still one only 1 pair.
- At the end of the second month the female produces a new pair, so now there are 2 pairs of rabbits in the field.
- At the end of the third month, the original female produces a second pair, making 3 pairs in all in the field.
- At
the end of the fourth month, the original female has produced
yet another new pair, the female born two months ago produces her
first pair also, making 5 pairs. (http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fibBio.html)
The number of pairs of rabbits in the field at the start of
each month is 1, 1, 2, 3, 5, 8, 13, 21, etc.
The Fibonacci Rectangles and Shell Spirals
We
can make another picture showing the Fibonacci numbers
1,1,2,3,5,8,13,21,.. if we start with two small squares of size 1 next
to each other. On top of both of these draw a square of size 2 (=1+1).
We
can now draw a new square - touching both a unit square and
the latest square of side 2 - so having sides 3 units long; and then
another touching both the 2-square and the 3-square (which has
sides of 5 units). We can continue adding squares around
the picture,
each new square having a side which is as long as the sum of the latest two square's sides.
This set of rectangles whose sides are two successive
Fibonacci numbers in length and which are composed of
squares with sides which are Fibonacci numbers, we will call the
Fibonacci Rectangles.
The
next diagram shows that we can draw a spiral by putting together
quarter circles, one in each new square. This is a spiral (the
Fibonacci Spiral).
A similar curve to this occurs in nature as the shape of a
snail shell or some sea shells. Whereas the Fibonacci
Rectangles spiral increases in size by a factor of Phi (1.618..) in
a
quarter of a turn (i.e. a point a further quarter of a
turn round the curve is 1.618... times as far from the
centre, and this applies to
all points on the curve), the Nautilus spiral curve takes a
whole turn before points move a factor of 1.618... from the centre.
A slice through a Nautilus shell
These spiral shapes are called
Equiangular or
Logarithmic spirals.
The links from these terms contain much more information on
these curves and pictures of computer-generated shells.
Here is a curve which crosses the X-axis at the Fibonacci numbers
The
spiral part crosses at 1 2 5 13 etc on the positive axis, and
0 1 3 8 etc on the negative axis. The oscillatory part crosses at 0
1 1 2 3 5 8 13 etc on the positive axis. The curve is
strangely reminiscent of the shells of Nautilus and snails.
This is not surprising, as the curve tends to a logarithmic
spiral as it expands.