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BIOLOGY
ORGANIC EVOLUTION
Prepared by SAIFAT
November 2016
Tanzania

ORGANIC EVOLUTION
Definition
Evolution is the process by which different kinds of organisms develops from complex form to
simple form due to change of adaptations
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THEORIES OF ORIGIN OF LIFE
Many scientists have tried to describe the origin of life on the earth
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”
It also explains that once organisms are created, they never change (they remain unchanged)
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Weakness of the theory
 It cannot be subjected into experiments (it is not scientific)
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(b) SPONTANEOUS GENERATION THEORY
In this theory it is believed that “Life originated from non living matter
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For example, they believed that;(i) Worms and tadpoles (young frogs) originated from the meat
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(iii)Lice originated from dirty etc
Strength of the theory
 It can be experimented (tested)
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(c) STEADY STATE THEORY
This theory states that “Life had no origin but the earth has been able to support it
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Strength of the theory
 It is true that life is supported by the earth
Weakness of the theory
 It is not true that life had no origin, life must have an origin
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” This
theory doesn’t show the specific part of the universe where life was brought, but it shows that
life is supported on the earth
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Weakness of the theory
 It does not tell the origin of life on earth
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(e) BIOLOGICAL EVOLUTION THEORY
In this theory it is believed that, “one billion years ago temperature and moisture became
suitable for life
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When these gases were exposed in ultraviolet light or electrical charges, ammonia acids were
formed
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Strength of the theory
 It is scientific and therefore can be experimented
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2
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OR
Organic evolution is the process which involves gradual and progressive changes of living
organisms over a million of years
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He formulated his theory and he called it Lamarckism based on two
theories which are;(i) The use and disuse of organs (parts)
(ii) Inheritance of acquired characters

In explaining his theory, he suggested that; A change in the environment creates new needs in the organisms living in that environment
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 He believed that during life time of an organism, those parts which are used tend to
develop and become strong while those parts which are not used weaken and disappear
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He used the following points (examples) to explain his theory;(a) DEVELOPMENT OF LONG NECKED GIRAFFES
According to Lamarck, the ancestral giraffes had short necks
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Due to
constant strengthening of the neck muscles while eating, the giraffes developed a long and strong
necks and front legs (use and disuse theory)
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(b) DEVELOPMENT OF WEBBED FEET IN DUCKS
Jean Baptist Lamarck assumed that today’s water birds were originally terrestrial (land) birds
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This acquired
character (webbed feet) was inherited generation to generation
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 He emphasized the role of environment in the course of evolution
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Weakness of Lamarck’s theory
 Acquired characters cannot be inherited generation to generation since they are not
controlled by genes
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 He didn’t distinguish inheritable from non- inheritable characters
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By using his ship HMS Beagle, he travelled for five years from South America to various parts
of the world
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 Organisms of the given area appeared related to the fossils of that area
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This news made Darwin to put forward his theory of organic evolution in form of a booklet titled
Origin of species by means of natural creation
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Darwin’s theory is based on three parts;(a) Survival of the fittest
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(c) Natural selection
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Darwin’s theory of natural selection is based on the number of observations and deductions
(conclusions);1st Observation
Organisms in a population tend to over-reproduce than the available resources
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2nd Observation
The number of individuals in a population remains fairly constant
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DEDUCTION 2
In the struggle for existence, those individual that are well adapted to the environment survive
and reproduce themselves while those individuals that are less adapted are selected out by nature
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Due to
lack of food on land, they both had to look for food on leaves of trees
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The short necked giraffes failed
in the struggle and therefore they died in the course of natural selection
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Strength of Darwin’s theory





It explains evolution more scientifically
It is true that variations occur among individuals
It shows the role of environment in evolution
It stopped the debate on the theory of special creation

Weakness of Darwin’s theory



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

He failed to distinguish continuous variation from discontinuous variation
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He failed to explain variations genetically
The theory failed to distinguish inheritable from non inheritable features
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MECHANISM OF ORGANIC EVOLUTION
This means what factors cause organic evolution and how they cause it
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This
change results into difference in characteristics (variations) and hence organic evolution
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This may cause changes in organisms and finally organic evolution
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Gene
flow may alter, add or remove certain characters in a population and hence gradual changes in
organisms (organic evolution)
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Since organisms occupy different habitats, then they never meet to carry out mating process
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(e) SELECTION
As in isolation, selection is also categorized into two categories;(i) Natural selection
This is a process by which the environment itself selects the organisms that are well adapted to
live in it
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The process by which new species arise (develop) naturally from the pre-existing species is
called Speciation
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(ii) Artificial selection
This is a careful and planned breeding done by man
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Artificial selection is categorized into two groups;(i) Inbreeding
This is the mating of organisms which are closely related such as brother and sister or father and
daughter in animals
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So artificial selection causes
variations and hence organic evolution
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Among of those evidences are;(a) Evidence from fossil records (Paleontology)
Fossils are preserved remains of animals and plants (organisms) e
...
bones, teeth, stems, leaves
etc
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This assures that
organic evolution takes place among individuals in specie
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This ensures that all
vertebrates originated from the same ancestors (old form of organisms)
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g
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These similarities in body functions (processes) indicate that animals originated from the
common ancestors
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Organisms are found (distributed) in different geographical locations
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Hence here adaptations is said to be the agent of evolution
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If the structures of the some organisms are
compared, they show some similarities which indicate a common origin
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g
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(ii) Homologous structures
These are body structures of different organisms that are similar but perform different
functions due to adaptations e
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fore limbs of vertebrates (in man for catching, in birds
for flying, in whales for swimming etc)
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g
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(iii)Vestigial structures
These are structures which have lost their function in a course of evolution
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g
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Other evidences of organic evolution can be derived from;(i) Taxonomy (the study of classification of organisms based on their relationships)
(ii) Cytology (the study of the cell structure of organisms)
(iii)Bio-chemistry (the study of compounds found on food samples e
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glucose)
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