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BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
Chapter 6
The biological basis of change
The biosphere: It is the space between the deepest parts in an ocean the
highest part on a mountain where life exists.
 The diversity of living organisms:
There is more than a million species of animals that differ in shape
and characteristics although they share the same basic characteristics
of life .
there are different theories about the diversity of the living organisms
these are:
Special creation theory
* Early ancestors of living
organisms were similar to the
present forms.
* The number of species is
constant.
* Each species is a special
creation.
Organic evolution theory
* Early present species of living
organisms evolved from an early
ancestor that was less
complicated.
* The number of species is
changing.
* No species is a special creation.
Mechanism of evolution
Evolution
 It is a gradual change that
that continues through a
long period of time and
leads to the appearance of
new species from old ones.
 Evolution may lead to
improvement.
Improvement
 It is a change that makes the
organ more able to carry out
its function.
 Not all evolution is an
improvement.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
Lamarck's theory
 The law of use and disuse:
"The organs that are used are strengthened while those which are
(disused) neglected will diminish or disappear."
The inheritance of the acquired characters:
"The acquired change in the organism by the use and the disuse of organs
is passed (inherited) to the following offspring"
Examples:
1- The neck of giraffe:
 Lamarck believed that the early ancestors of giraffe were shortnecked.
 When the grass lands dried up and only tree leaves were
available some of the short-necked giraffes perished while
others stretched their necks to get leaves, so, their necks became
longer because of using them.
 The long necked giraffes passed their acquired character to their
offspring.
2- The disappearance of hind limbs in whales………..why?
 Because they disused or neglected the using of them and the use
of the tail as a locomotory organ.
3-The disappearance of limbs in snakes………………why?
* Because they were neglecting using their limbs gradually through the
generations because they were forced to escape and hide in narrow holes.
Criticism of Lamarck's theory (Objection against Lamarck's theory)
 Blacksmith: The runner whose leg muscles are well-developed
does not pass this to his children.
 Weismann: Proved experimentally that acquired characters are
not inherited, by cutting rat tails after they were born for 19
generations.
 In each generation every rat was born with a tail.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
Darwin's theory
Darwin's opinion about evolution depends on the following:
1-Great productivity: (struggle for survival)
*Most of live in organisms produce great numbers of offspring.
* the number of individuals of any species remains constant for long
periods due to the competition between them for food and shelter, this
called "struggle for survival( existence) "
2-Variation and differences:
 -No individuals are completely identical, even twins.
 Variation means that some organisms are fit that can survive
and win the life struggle and others are weak which can not
survive, so, they will be extinct.
3- Natural selection:
 Natural selection means the selection of the fittest individuals
that can win the life struggle and survive, while weak
individuals die.
 Natural selection occurs by other living components in the
environment.
 The fittest organisms are those that can win the life struggle
and survive.
4-Transformation and changes:
Darwin's explanation of the long neck of the recent giraffe:
 According to Darwinism, giraffe's ancestors were short-necked
but few of them were long-necked.
 When the grass lands dried up and only tree leaves were
available, only long necked giraffes were able to get the leaves
of high trees easily, so they won the life struggle and survived,
whereas the short-necked died up became extinct. By the
repetition of natural selection the present long-necked species
evolved.
Criticism of Darwin's theory:
1- Most of the changes discussed by Darwin are somatic changes and not
hereditary.
2- The struggle for existence is not general and is not enough to cause the
extinction of species.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
3- The struggle for existence does not explain the sudden disappearance
of the giant reptiles (dinosaur).
4- Darwin's theory does not explain the sudden appearance of some traits.
The modern synthetic theory
Simpson, Julian Huxley and others
 It explains the appearance of new species to the changes in the
population not in the individuals.
 The factors that lead to evolution are:
1- population genetic:
A population is a group of individuals of a certain species living in a
certain environment and inbreed freely.
A Common gene pool is the genes of all characters in all individuals in
any population.
According to modern synthetic theory:
Genetic equilibrium:
"The tendency of the ratio of gene distribution among individuals of the
population to be constant from generation to another"(Hardy&Weinberg)
Conditions that keep the genetic equilibrium or balance in the
population are:
The population must be large in size.
Individuals should mate at random.
The hereditary traits should not be subjected to natural selection.
Individuals should not emigrate from the population or immigrate to it.
Mutation should not occur.
Genetic drift is a disturbance in the genetic equilibrium of the
population if one of its conditions is not fulfilled.
 Genetic drift causes the evolution of the population.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
 Isolation and speciation:
Anagenic speciation
 The individuals inside the
population live together
without spreading.
 They are exposed to small
mutations and variations
at successive generations.
 The accumulation of these
characters leads to the
appearance of new species.
Phyletic speciation
 In which small groups of
individuals leave the
original population and
spread in different
directions.
 These small groups become
isolated, so that led to
appearance of new species
"adapt to the new
environment.
 Ex.: Darwin's finches in
Galapagos.
 Give reasons for:
1-Before the industrial revolution in England, the light coloured
Biston betularia butterflies were save.
* Because they can not seen by their enemies while resting on tree trunks,
so, the natural selection was in favour of light coloured butterflies and
against the black.
2- Some of the cepia nemoralis snails are abundant, while others are
rare.
* Because these snails are characterized by different colors and lines
inherited by many genes. The abundant group resembles the environment
in color, so, it is not seen by their enemies, but the rare group does not
have this advantage, so, they are easily picked by birds.
3- Darwin's finches are god example for phyletic speciation.
4- The disappearance of the hind limbs in while (in view of Lamarck).
5- The disappearance of limbs in snakes ( in view of Lamarck).
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
Evidences that support evolution
1-Fossils and evolution:
Fossils: they are remains or traces of living organisms that lived in the old
ages.
 The conditions for fossil formation:
 The organism must have a hard skeleton.
 The organism must be buried in sediments soon after death….why?
* To protect it from decay.
 Mineral replacement or petrifaction was occurred.
Type of fossils
 Fossil of entire organism (Mammoth)
 Fossil of hard parts (bones, teeth and shells)
 The petrified remains:
 Petrifaction or mineral replacement is the transformation of
the solid organic parts into mineral substances.
 Moulds and casts:
Solid mould: a fossil that shows the internal details of the mollusc.
- When a mollusc dies, it falls to the bottom of the sea and is buried in
sand (sediments)
- The sediments fill the cavity of the mollusc, then stick together and
change into rocks.
The cast: it is the mark left by the body of the organism when it touches
the soft sediment after death.
- A leaf falls on a muddy surface and disintegrates (decays)
 The prints: They are marks left by the organism in the soft sediments,
when it was alive.
-Animals left their foot prints.
From the study of the fossil record it was concluded that:
- Life started in water and gradually moved to the earth.
- The evolution of life moved in the direction of increasing
specialization and complexity.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
- Algae appeared before mosses and ferns, and gymnosperms came
before angiosperms.
- Invertebrates appeared before vertebrates.(fish is the first group).
The roles(importance) of fossils are
1- They are used as tools to identify and compare between different layers
of sedimentary rocks.
2- Fossils can also be used as intermediate links (Archaeopteryx).
2- Taxonomy and evolution:
* The gradation of development in the tree of life shows the idea of
evolution that indicates that different species and genera of each family
have a common origin.
Intermediate link: it is a contemporary or extinct species of living
organism that has characters of two successive classes of living
organisms.
Give reasons :
 The fossil of Archaeopteryx represents an intermediate link
between reptiles and birds.
- Because it has some of the reptiles characters which are : teeth, long
tail and claws.
- It has some of birds' characters such as: beak, wings and the shape of
the skull.
 The lung fish is an intermediate link between fish and amphibians.
- Because it respires by gills as in fish, but when drought comes its air
sac changes to look like a lung that gets oxygen from air as in
amphibia.
3-Vestigial organs and evolution:
Vestigial organs are organs which used to be well developed in early
ancestors of vertebrates but they disappeared or diminished in
contemporary species.
Give reasons for: The appendix in man supports evolution.
- The appendix is reduced in size in the present day man, large in
herbivores (Rabbit) and missing in carnivores.
- The appendix is used to digest cellulose, so, they were developed in
ancient man who used to feed on plants.
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M.A.BARAKAT
0126375561
BIOLOGY
SEC.1
‫خاص بالمجموعات المدرسية‬
4-The comparative anatomy and evolution:
- Limbs with five digits (pentadactyl limbs) Originate first and all
vertebrate limbs developed from it.
- In both birds and bats, the fore limbs are modified into wings.
- In Hoofed animals, the digits are reduced to one.
- In Whales and Dolphin, the bones are fused to form an oar.
- All vertebrates have a common origin.
5-The physiological resemblance and evolution.
* It is evidence that living organisms have a common origin.
* Metabolism take place in identical way in all living organisms.
* The cell division follows the same steps in all living organisms.
* Getting rid of nitrogenous wastes is evidence that supports
evolution.
* Fish and aquatic animals get rid of their wastes through gills in form of
ammonia.
* Frogs and mammals: convert ammonia into urea which is excreted in
the urine.
* Birds, Reptiles and Insects get rid of their wastes in the form uric acid.
*Tadpole: get rid of nitrogenous wastes in the form of ammonia.
6- Embryology is an evidence that support evolution:
* The embryos of certain vertebrates pass through a stage where the body
has gills, gills slits and a heart of one auricle and one ventricle as in fish.
But gills disappear (except in fish) and the heart becomes of two auricles
and two ventricles
* This is also applied for the growth of the brain and the organs of
excretion, reproduction and skull bones.
6- The geological (geographical) distribution and evolution:
Give reasons for:
 Animals of south America are different from those of Africa
despite the similarity in the climate of both areas.
-Due to the ancient separation of the two continents and the presence of
natural barriers (the ocean) between them, so animals evolved
independently from each other.
The animals of British Islands resemble those of Europe although
they are separated.
- Because the separation of England from Europe is relatively recent.
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M.A.BARAKAT
0126375561