Organic evolution is the theory that all living organisms are descended from common ancestors, and that changes in their genetic makeup over time have led to the diversity of life on Earth by Sanju Sah.pdf

Organic evolution is the theory that all living organisms are descended from common ancestors, and that changes in their genetic makeup over time have led to the diversity of life on Earth

1. Organic Evolution
By- Sanju Sah
Lecturer at Dhanwantri Ayurbigyan Sansthan and Hospital, Thapagau
An Alumni of St. Xavier’s College, Maitighar

Life originated on primitive earth by chemical evolution and it was later replaced by
Organic evolution.

• Organic evolution is the slow, progressive, continuous and irreversible change of
organisms from simple to complex forms over a long period of time.

• Father of the concept of organic evolution is Ampedocles.

2. Evidences of Organic Evolution




• From the comparative study of morphology, anatomy, fossils, embryonic
developments, biochemistry and serology, scientists have gathered
evidence of organic evolution.

• The important evidences of organic evolutions are described below:

1. Evidences from morphology and anatomy
• Comparative study of animals shows similarities in their organizations.
• Three types of organs (homologous, analogous and vestigial) in
different groups of animals provide evidence in favor of evolution.

3. A. Homologous organs:
• Organs which have similar structure and origin but perform different
functions are called homologous organs.

• For e.g. forelimbs of whale, bat, bird, horse, frog man etc. are
functionally different i.e. forelimbs of whale are modified for
swimming, of bat and bird for flying, of horse for running, of frog for
jumping and of man for grasping. But the forelimbs in all these
animals have the same skeletal plan consisting of the same set
of bones which are humerus, radius-ulna, carpals, meta-carpals
and phalanges.

• Hence though these animals look different, a comparison of their
homologous organs indicate that these animals must have evolved
from a common ancestor.

5. B. Analogous organs
• Those organs which are structurally different but functionally
similar are called as the analogous organs.

• Analogous organs do not have a common embryological origin. For
e.g. wings of Insect, bat and birds.

• The wings of these animals have a similar function of flight but they are
structurally different. The wings of an insect is membranous and is not
attached to bones. In birds, wings are made up of feathers which are
attached to bones of arms whereas in bat, wing is formed of a fold of skin
called patagia and it is also attached to the bones of arms.

6. • Other examples of analogous
organs are: flippers of whales
and fins of fishes.

•These organs suggest that the
organisms might have evolved
from different ancestors and had
convergent evolution.

7. C. Vestigial organs



• Those organs which are present in the
body but remain unused or non -
functional are the vestigial organs.

• For e.g. vermiform appendix, wisdom teeth,
body hair, external ear (pinna), caudal
vertebrae-coccyx, nictitating membrane etc.

• Vestigial organs were fully developed and
functional in the ancestral forms but later
they became reduced and non- functional
due to change of habit, habitat and other
environmental factors.

8. • In herbivorous animals like rabbit, vermiform appendix is well
developed and helps in digestion of cellulose present in vegetable
matter. Man’s ape-like ancestors were also herbivorous and had
developed vermiform appendix but the present day man turned
omnivorous and because of this change in diet, the appendix have
become greatly reduced and functionless. Thus we can conclude
that man has descended from ancestors in which these organs were
functional.
D. Atavism or reversion:
• The sudden reappearance of ancestral characters is called
Atavism.
• For e.g. presence of short tail, pointed canine teeth etc.

9. 3. Evidence from
embryology


• Embryology is the study of formation and
development of embryo in animals.


• The evidences provided by embryology are as
follows:

a) Similarity in vertebrate embryos:
• Young embryo of all vertebrates from fish to
mammals have similarities that make impossible to
distinguish one from other. This similarity indicates
having common ancestors.

10. b) Similarity in early development of animals:
• The early developmental stage of all multicellular organisms are
similar with the following common stages :
• egg- zygote – morula –blastula –gastrula – formation of 3 germ
layers- formation of different organs.

C) Recapitulation theory (Biogenetic law)
• Embryological evidence is also supported by Haeckel with his
“Recapitulation theory” or Biogenetic law. It states that “Ontogeny
repeats phyllogeny” which means that all organisms repeat their
ancestral history during their embryonic development. For
example: Tadpole of frog is tailed, has gills and is aquatic. It signifies
that frogs must have evolved from fish.

11. Evidence from paleontology



• Paleontology deals with the study of fossils.

• Fossils are any form of preserved remains or traces of ancient organisms preserved
in the rocks or anywhere else in the earth.

•The process of fossil formation is called fossilization.

•Age of fossils is determined by radiocarbon dating technique.

12. 2. Evidence from paleontology


Types of fossils:

• Intact fossils: Entire organisms get preserved mostly due
to freezing in ice without any decaying and
decomposition. Eg. Wooly mammoth



• Petrified fossils: Most usual types of fossils. Soft parts
disintegrate and the hard parts of body like bones, teeth
and exoskeleton get replaced by mineral deposits.
Replacement of organic parts by mineral deposits is
called petrifaction.

13. Impressions / Impressions :
When the organism or certain parts of ogranism come in
contact with soft clay, they leave an impression on the soil
which later on harden to form rocks. Eg; footprints of
dinosaur.




Casts / Moulds :
Mold forms when hard parts of an organism are buried in
sediment. Hard parts dissolve over time leaving a hollow area
with the organism's shape which is called mold.
A cast forms when minerals fill the mold's empty spaces.

14. Evidences provided by fossils
:


1.

Fossils found in older rocks or deeper parts of
rocks were of simpler types and those found in
comparatively newer rocks or upper part of
rocks are of complex
organisms
which
indicates that

evolution has taken place
gradually from simple to complex

organisms.



2.

Fossil records help us explain the evolutionary
history (phylogeny) of the organisms. The
phylogeny of horse has been made possible
through its fossils records in sedimentary rocks of
North

America.

15. •

Some fossils provide evidence for connecting link between
2
groups
of organisms. Example:
Archaeopteryx
is a fossil
bird which is a connecting link between
reptiles
and

birds.


•

It
had a beak like a bird but its jaw
was
provided with

teeth

like reptiles.

•

It
had wings like birds but wings had claws like

reptiles.

•

It
had feathers like birds but also had scales like

reptiles.

•

It had a feathery tail like birds but also had tail vertebrae

like

reptiles.


Hence,
fossil of
Archaeopteryx
has provided evidence on

origin of birds from reptiles.

16. Evidences from Biochemistry

Following biochemical characters of animals also provide evidence in favour of
evolution.
1. Similarity in chemical composition :
All living organisms are composed of 4 fundamental organic compounds i.e.
carbohydrates, fats, proteins and nucleic acids in their protoplasm which suggests a
common origin.
2. Enzymes and hormones :
• Presence of identical enzymes and hormones in large group of organisms
suggest a common origin. Several digestive enzymes like amylase, trypsin
and lipase and hormones like thyroid hormone are common in wide variety of
animals.

17. 3. Serological tests:
• It determines the relationship between different
organisms on the basis of similarity of their
blood proteins.

• Blood proteins are similar in closely related
Organisms than distantly related ones.

• Serum of closely related animals is unable to
produce precipitation whereas those of
distantly related animals produces
precipitation.

• These precipitation tests have demonstrated that
human blood proteins are similar to those of
apes, gorilla, chimpanzee and monkey.

18. 1. Divergent evolution / Adaptive
radiation :
• Evolution of a number of different
groups of organisms from a common
ancestral group is called divergent
evolution.

• Divergent evolution leads to production
of homologous similarity.

2. Convergent evolution :
• Unrelated species become more and
more similar in appearance as they
adapt to the same kind of
environment. Most common
examples of convergent evolution is
the development of wings in insects,
birds and bats.

• Convergent evolution leads to the
production of analogous

19. similarity
among organisms of different groups.