ORIGIN AND EVOLUTION OF LIFE
ORIGIN OF LIFE::
The earth was formed about five billion years ago. At that time it was extremely
hot. The existence of life in any form at that high temperature was not possible. Origin of life means the appearance of simplest primordial life from nonliving matter.
Special creation theory:-
This theory was forwarded by Spanish priest, father Suarez. According to this theory the entire living things and earth was made by god. God created living things and other in 6 natural days. They are:-
1st day- god created earth and heaven
2nd day-god created sky
3rd day- the sun, moon, stars.
4th day-god created plants and animals
5th day-fishes and birds
6th day- human(Adam & eve)
2. Abiogenesis theory:-
According to this theory, living being ere automatically originated from none living things. The ancient Greek philosophers were the supporter of this theory.
Thales believed that life originated from water
Anaximander believed that life originated from primordial soup.
Empedocles believed that life originated from some attractive and repulsive forces.
Aristotle believed that living organism originated from non living things .e.g. frog from mud, mice from wheat
Abiogenesis theory is not accepted now days.
3. Biogenesis theory:
a.Francesco redi’s experiment:
Francesco Redi, who lived in the seventeenth century, did not believe in spontaneous generation. He explained the presence of worms in decayed meat and that the putrefied matter in which they are found has no other office than that of serving as a place, or suitable nest, where animals deposit their eggs at the breeding season, and in which they also find nourishment: otherwise, I assert that nothing is ever generated therein …”
Redi carefully observed the worms – we would call them maggots – on decaying meat exposed to the air. About nineteen days after they had first appeared he saw that some of them had turned into pupae, which he collected and placed separately in glass vessels. Eight days later he saw flies hatch out of the pupae. Here, then, was proof.
By this painstaking work Redi had recorded things which the believers in spontaneous generation had either not seen or ignored. Their understanding had been limited by the extent of their observations. Redi extended his observations and thus provided support for his new idea. This comparison bears out the truth of the saying that we can only see as far as we look. Possibly Redi’s persistent observations were encouraged by his beliefs just as those of his opponents were discouraged.
B.lazzaro spllanzani’s experiment:-
In 1668, Francesco Redi, a physician, naturalist and Italian poet, made a couple of experiments which showed that insect larvae hatched from. Influenced by Galileo Galilee, who held that one could see the world through the use of the senses, applied an experimental method to test their ideas, which became one of the first experimental biologists.
Redi claimed that maggots hatched from eggs, deposited by flies. To test his idea pieces of meat placed in wide mouth jars, leaving some open and some closed tightly. A few days later found maggots in open bottles, but not in the closed. ¿It tasted the meat itself did not generate worms? Those who thought they could generate spontaneously (spontaneists) argued that the lack of air in closed vials prevented the worms live. Redi repeated the experiments, but this time a few bottles closed with fine gauze. As these worms appeared not concluded that this was because the flies could not enter and lay eggs.
C.louis Pasteur:-
Louis Pasteur designed an experiment to test whether sterile nutrient broth could spontaneously generate microbial life. To do this, he set up two experiments. In both, Pasteur added nutrient broth to flasks, bent the necks of the flasks into S shapes, and then boiled the broth to kill any existing microbes.
After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above. The flasks in Experiment 2 were left alone.
Over time, dust particles from the air fell into the broken flasks of Experiment 1. In Experiment 2, dust particles remained near the tip of the swan necks, but could not travel against gravity into the flasks, keeping the nutrient broth sterile.
The broth in the broken flasks quickly became cloudy--a sign that it teemed with microbial life. However, the broth in the unbroken flasks remained clear. Without the introduction of dust--on which microbes can travel--no life arose. Thus, the Louis Pasteur experiment refuted the notion of spontaneous generation.
4. Oparin and Haldane’s theory:-
Several theories were put forth to explain origin of life. The widely accepted theory
Is the (Chemosynthetic theory of origin of life proposed by A.I. Oparin). Oparin and Haldane’s theory states that Life might have first originated on earth through a series of combinations
of chemical substances in the distant past and it all happened in water.
They told that life was originated on following ways:-
Chemogeny
Biogeny
Cognogeny
Chemogeny: The earth originated about 5 billion years ago.
l It was initially made up of hot gases and vapours of various chemicals.chemogeny is the chemical evolution on earth. It is further divided into:
Formation of simple compounds
In the primitive earth, the condition was favorable for chemical evolution. Formation of methane,ammonia,water vapour,carbon dioxide took place in primitive earth by the reaction of elements like H,O,C,N.formation of water vapour was the of rainfall and temperature of earth cooled down gradually.
Formation of simple organic compounds
The simple organic compounds were created in the oxygen less atmosphere by the reaction of simple compounds under the action of uv rays and lightening. Simple organic compounds were alcohols, aldehydes, amino acids, glycerol, fatty acid, simple sugar, purines and pyramidines. They were formed in hot water o earth and called as broths.
Formation of complex organic compounds
By the combination of simple organic compounds, complex organic compounds were formed in the earth. They were polysaccharides, fats, proteins, nucleic acids, carbohydrates etc.formation of protein and nucleic acid was the important part
In chemical evolution.
Biogeny: it is the process of biological evolution on earth. It took place after chemogeny.th includes:
a. Formation of coacervates:-
The complex organic compounds of oceanic soup were accumulated due to intermolecular attraction and formed a large and highly organized colloidal system called as coacervates. They possess the ability to exchange energy and grow. After attaining larger size, they use to break down and multiply. They were the intermediate between molecule and living cell.
B. origin in of prokaryotes:
Prokaryotes means organism having prokaryotic cell.fromcoacervates, prokaryotes were formed. The first prokaryotes were anaerobic chemo heterotrops.according to haldene,the first cell like structure is known as eobionts.
They were originated about 3800-4800 million years ago.From heterotrops, auto tropes were formed in following manner:
Anaerobic anaerobic anaerobic aerobic
Chemo chemo photo photo
heteroyrops autotrops autotrops autotrops
E.g. sulphur e.g. green e.g.
Bacteria s.bacteria cyanobacteria
Cyanobacteria were oxygen producer:
Co2 +h2o C6H12O6+O2
C. origin of eukaryotes:-
The organisms having eukaryotic cells are called as eukaryotes. They were developed from prokaryotes. The first eukaryotes developed 2700million years ago. The free living eukaryotes were developed 1600 years ago. Evolution of eukaryotes proceeds fast due to the presence of free molecules of oxygen.
Cognogeny:-
It is the evolution of higher organism from lower organism by modifying characters.
It deals about the development of body structure, body system, modification of life etc.it helped to form developed eukaryotes. The eukaryotes changed themselves according to land, climate etc and formed diverse form of life.
Miller and Urey experiment:-
Stanley miller and herlod Urey did an experiment to test oparin and Haldane’s theory in 1953.they did following experiments:
They took mixture of gases (hydrogen, methane, ammonia, water vapour) in a closed gas chamber. They set the apparatus as shown in the figure.
They took boiling water in another closed liquid chamber. The mixture of gases resembles the gases of primitive earth and the hot water resembles the hot water of oceanic soup of primitive age.
They supplied high voltage current i.e. 70000 volts through two electrodes in that glass chamber. The current supplied resembles the source of energy i.e. lightening at primitive earth. They left the apparatus for 2 weeks in lab. After 2 weeks they found that organic compounds were formed in the trap by the continuous reaction of gases. They synthesized amino acids, sugars and other compounds from the trap. Amino acids were glycine and alanine.
They found that organic compounds important for life were obtained from inorganic gases. They strongly supported oparin and Haldane’s theory that life was originated from non living chemicals.
Organic evolution:-
What is Evolution?
The formation of complex organisms through ‘change’ from simple ancestral types
Over the course of geological time.
According to the Theory of Organic Evolution
The various present day organisms were not created in the same form in which
they exist today, but have gradually evolved from much simple ancestral forms
of a common ancestor.
The characteristics of organism had been changing in the past; they are changing
even today, and will continue to do so in the future as well. This is due to the
fact that the environment in which organisms live also changes and organisms
need to be adapted to survive in the changed environment.
Many living organisms of the past have become extinct.
The origin of the various forms (species) found on earth has been a gradual
and extremely slow process, requiring hundreds or even thousands of years.
This process of slow and gradual change is called organic evolution.
Thus, the theory of organic evolution states that “All living things on earth
are here as a result of descent, with modifications from a common
Ancestor.
Types of organic evolution:-
Divergent:- it is a type of evolution in which different group of organisms or species evolve from a same common ancestor and occupied different places.
E.g. whale, bat, horse
Convergent:- it is a type of evolution in which different unrelated organism evolve from different ancestor but occupy same habitat.
E.g. whale, fish
Parallel:-it is a type of evolution in which different species of common ancestor occupy same evolutionary path.
E.g. new world porcupines and old world porcupines.
Progressive:-it is a type of evolution in which simple organisms developed toward complex organism.
E.g. Formation of multicellular organism from unicellular.
Retrogressive:-it is a type of evolution in which characters are gradually decreased from complex to simple.
E.g. parasites look simple but are more advanced.
Evidences of organic evolution
The evidences supporting organic evolution are derived from a number of fields
of Biology. Those discussed here are -
1. Morphological evidences
2. Embryological evidences
3. Paleontological evidences
4. Molecular evidences
1. Evidences from Morphology
Though organisms of different species and groups are quite different from each
other still they retain certain common features. Morphological evidences for
evolution are derived from -
(i) Homologous and analogous organs
(ii) Vestigial organs
(iii) Connecting links
The comparative study of various organs in different groups of vertebrates exhibit
common features which shows that they evolved from a common ancestor. Take
for example that of the heart of the vertebrates
(i) Homologous Organs
Homologous organs are the organs which are similar in structure and origin but
may look very different and perform different functions.
– Fore limbs of vertebrates are a good example of homologous organs. They are
built on the same fundamental plan yet they appear differently and perform
different function.
– In each case the fore-limb consists of humerus, radius and ulna, carpals,
metacarpals and phalanges. This basic similarity in the structure of the
apparently different fore limb of different kinds of vertebrates is due to the fact
that all these limbs have been evolved from a common type called the
pentadactyl (five-fingered) limb.
The homologous organs, therefore, prove that there has been evolution and not
creation.
(ii)Analogous organs
The structure which are functionally similar but structurally different are called
analogous organs.
The wing of an insect, and that of a bird or bat or pterodactyl are examples of
analogous organs . The function of the wing is the same (for flying) but
the insect wing has no structural resemblance with that of the vertebrates.
(a) Wing of insect (b) Wing of bird
(iii) Vestigial Organs
Vestigial organ is any small degenerate or imperfectly developed (non-functional)
organ or part which may have been complete and functional in some ancestor.
The only rational explanation for the presence of these non-functional organs is
That they are inherited from ancestors in which they were functional. shows
Some of the vestigial structures in human body.
Example of vestigial organ are nictitating membrane of human eye, molar teeth, appendix,pinnae etc.
(iv) Connecting Links
The animals or plants which possess
characters of two different groups of
organisms are known as connecting links.
The connecting links establish continuity
in the series of organisms by proving that
one group has evolved from the other. A
good example is that of a fossil bird
Archaeopteryx, which was a connecting
link between reptiles and birds. This bird
had a beak with teeth and a long tail (with
bones) like the lizards. It had feathers on
the wings and on the body like the birds.
Characteristics feature of archaeopteryx:-
It was the connecting link between reptilian and aves.it has intermediate characters of both.
It was found in the Jurassic period. It is known as lizard bird.
Body was covered with feather like apes and scales like reptile.
Fore limbs were modified into wings like bird and contain claws at top like reptile.
Head contain beak and teeth both.
Limbs were both for flying and climbing.
Contain long tail like reptile and covered with feather like bird.
2. Evidences from Embryology
Embryology is the study of development of an organism
The aspects of embryology which support the doctrine of organic evolution are :
similar stages of early development (morula, blastula or gastrula) in all the
animals;
the embryos of all vertebrates are similar in shape and structure in their early
stages.
This resemblance is so close that it is difficult to tell them apart
All the vertebrates start their life from a single cell, the zygote.
All of them during their life history, pass through two-layered blastula and three
layered gastrula stage and then through fish like stage with gill-slits.
All the different aspects of embryology strongly support the fact that the different
classes of vertebrates possess a common ancestry, and have differentiated from one
another through the process of evolution.
3. Evidences from Paleontology
Paleontology is the study of fossils. Fossils are the remains or traces of
animal and plant life of the past, found embedded in rock either as petrified
hard parts or as moulds, casts or tracks.
The fossils of the earliest era in the geological time scale were those of bacteria,
then invertebrates and then successively of fishes, amphibians, reptiles and lastly
of birds and mammals and among mammals primitive fossils of humans are the
most recent.
The fossils discovered provide the ancestral history of individual. Animals like
horse, camel etc. are direct proofs of organic evolution. This can be very well
illustrated by the past history of horse . The number of toes decreased
for greater speed, size gradually increased and teeth adapted to eat grass.
Importance of paleontology:-
It gives direct evidences of evolution.
It helps to know habit, habitat, behavior, feature of past or extinct organism.
It helps to find out the phylogeny of organisms.
Fossil of archaeopteryx is connecting link between bird and reptile.
It help to know the nutrition of past animals
It suggests that simple organism developed toward complex.
Types of fossils:-
Cast or mould: it is the hard covering of fossilized animal. If any organism die and gets preserved in clay or sediment, then clay or sediment becomes the cast or mould.
It helps to study external feature.
Amber: the fossil which is formed in resin or waxy substance of plant like pinus is known as amber. Mainly insects are preserved in resin.
Imprint: the sign or marks of ancient organism is known as impression or imprint.
Impression or imprint are found in clay or sediment. It is formed when the body decompose and only sign or mark is left.
Petrification: the fossil which is formed by the deposition of minerals in place of organic matter of organism is known as petrified fossils.
Compressed:-the fossil which are formed by the pressure of layer of earth is known as compressed fossil. If any organism is buried in lower layer of earth and preserved, then compressed fossil is formed.
4. Evidence of Evolution from biochemistry:
It gives the evidences of evolution, by the common similarities of chemicals in organism.
The common similarities are:-
Protoplasm: protoplasm is the physical basis of life. Protoplasm is made up of same basic elements in all organisms. The elements are water, carbohydrate, protein, fat, vitamin, minerals, enzymes etc.
Chromosome: it is the genetic material which carries characters from one generation to other generation. It is made up of nucleic acid and protein (histone and protamine). Basic component is same in all organisms.
Enzyme: enzyme is the bio-catalyst secreted by exocrine glands. Trypsin is the common enzyme from protozoa to mammal. Like wise amylase is the common enzyme from porifera to mammal.
Hormone: it is commonly called as chemical messenger. Hormones are secreted by endocrine gland. Thyroxin hormone is common in vertebrates. The activity of thyroxin hormone is same in all vertebrates.
Haemin crystal: when haemoglobin is added in acetic acid, then crystal is formed known as haemin crystal. If the shape and size of haemin crystal in two organism is same, then thy are closely related. If the shape and size of haemin crystal in two organisms is not same, then they are not closely related. Haemin crystal measures the degree of relationship between organisms.
Serum: the watery portion of the clotted blood is known as serum. The study of serum is known as serology. When the serum of closely related species is mixed, then it gives white precipitate. White ppt. is formed by the reaction of antigen and antibody.
Antigen: foreign protein in body e.g. virus, snake venom.
Antibody: chemical substance formed by body to fight with antigen.
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ORIGIN OF LIFE::
The earth was formed about five billion years ago. At that time it was extremely
hot. The existence of life in any form at that high temperature was not possible. Origin of life means the appearance of simplest primordial life from nonliving matter.
Special creation theory:-
This theory was forwarded by Spanish priest, father Suarez. According to this theory the entire living things and earth was made by god. God created living things and other in 6 natural days. They are:-
1st day- god created earth and heaven
2nd day-god created sky
3rd day- the sun, moon, stars.
4th day-god created plants and animals
5th day-fishes and birds
6th day- human(Adam & eve)
2. Abiogenesis theory:-
According to this theory, living being ere automatically originated from none living things. The ancient Greek philosophers were the supporter of this theory.
Thales believed that life originated from water
Anaximander believed that life originated from primordial soup.
Empedocles believed that life originated from some attractive and repulsive forces.
Aristotle believed that living organism originated from non living things .e.g. frog from mud, mice from wheat
Abiogenesis theory is not accepted now days.
3. Biogenesis theory:
a.Francesco redi’s experiment:
Francesco Redi, who lived in the seventeenth century, did not believe in spontaneous generation. He explained the presence of worms in decayed meat and that the putrefied matter in which they are found has no other office than that of serving as a place, or suitable nest, where animals deposit their eggs at the breeding season, and in which they also find nourishment: otherwise, I assert that nothing is ever generated therein …”
Redi carefully observed the worms – we would call them maggots – on decaying meat exposed to the air. About nineteen days after they had first appeared he saw that some of them had turned into pupae, which he collected and placed separately in glass vessels. Eight days later he saw flies hatch out of the pupae. Here, then, was proof.
By this painstaking work Redi had recorded things which the believers in spontaneous generation had either not seen or ignored. Their understanding had been limited by the extent of their observations. Redi extended his observations and thus provided support for his new idea. This comparison bears out the truth of the saying that we can only see as far as we look. Possibly Redi’s persistent observations were encouraged by his beliefs just as those of his opponents were discouraged.
B.lazzaro spllanzani’s experiment:-
In 1668, Francesco Redi, a physician, naturalist and Italian poet, made a couple of experiments which showed that insect larvae hatched from. Influenced by Galileo Galilee, who held that one could see the world through the use of the senses, applied an experimental method to test their ideas, which became one of the first experimental biologists.
Redi claimed that maggots hatched from eggs, deposited by flies. To test his idea pieces of meat placed in wide mouth jars, leaving some open and some closed tightly. A few days later found maggots in open bottles, but not in the closed. ¿It tasted the meat itself did not generate worms? Those who thought they could generate spontaneously (spontaneists) argued that the lack of air in closed vials prevented the worms live. Redi repeated the experiments, but this time a few bottles closed with fine gauze. As these worms appeared not concluded that this was because the flies could not enter and lay eggs.
C.louis Pasteur:-
Louis Pasteur designed an experiment to test whether sterile nutrient broth could spontaneously generate microbial life. To do this, he set up two experiments. In both, Pasteur added nutrient broth to flasks, bent the necks of the flasks into S shapes, and then boiled the broth to kill any existing microbes.
After the broth had been sterilized, Pasteur broke off the swan necks from the flasks in Experiment 1, exposing the nutrient broth within them to air from above. The flasks in Experiment 2 were left alone.
Over time, dust particles from the air fell into the broken flasks of Experiment 1. In Experiment 2, dust particles remained near the tip of the swan necks, but could not travel against gravity into the flasks, keeping the nutrient broth sterile.
The broth in the broken flasks quickly became cloudy--a sign that it teemed with microbial life. However, the broth in the unbroken flasks remained clear. Without the introduction of dust--on which microbes can travel--no life arose. Thus, the Louis Pasteur experiment refuted the notion of spontaneous generation.
4. Oparin and Haldane’s theory:-
Several theories were put forth to explain origin of life. The widely accepted theory
Is the (Chemosynthetic theory of origin of life proposed by A.I. Oparin). Oparin and Haldane’s theory states that Life might have first originated on earth through a series of combinations
of chemical substances in the distant past and it all happened in water.
They told that life was originated on following ways:-
Chemogeny
Biogeny
Cognogeny
Chemogeny: The earth originated about 5 billion years ago.
l It was initially made up of hot gases and vapours of various chemicals.chemogeny is the chemical evolution on earth. It is further divided into:
Formation of simple compounds
In the primitive earth, the condition was favorable for chemical evolution. Formation of methane,ammonia,water vapour,carbon dioxide took place in primitive earth by the reaction of elements like H,O,C,N.formation of water vapour was the of rainfall and temperature of earth cooled down gradually.
Formation of simple organic compounds
The simple organic compounds were created in the oxygen less atmosphere by the reaction of simple compounds under the action of uv rays and lightening. Simple organic compounds were alcohols, aldehydes, amino acids, glycerol, fatty acid, simple sugar, purines and pyramidines. They were formed in hot water o earth and called as broths.
Formation of complex organic compounds
By the combination of simple organic compounds, complex organic compounds were formed in the earth. They were polysaccharides, fats, proteins, nucleic acids, carbohydrates etc.formation of protein and nucleic acid was the important part
In chemical evolution.
Biogeny: it is the process of biological evolution on earth. It took place after chemogeny.th includes:
a. Formation of coacervates:-
The complex organic compounds of oceanic soup were accumulated due to intermolecular attraction and formed a large and highly organized colloidal system called as coacervates. They possess the ability to exchange energy and grow. After attaining larger size, they use to break down and multiply. They were the intermediate between molecule and living cell.
B. origin in of prokaryotes:
Prokaryotes means organism having prokaryotic cell.fromcoacervates, prokaryotes were formed. The first prokaryotes were anaerobic chemo heterotrops.according to haldene,the first cell like structure is known as eobionts.
They were originated about 3800-4800 million years ago.From heterotrops, auto tropes were formed in following manner:
Anaerobic anaerobic anaerobic aerobic
Chemo chemo photo photo
heteroyrops autotrops autotrops autotrops
E.g. sulphur e.g. green e.g.
Bacteria s.bacteria cyanobacteria
Cyanobacteria were oxygen producer:
Co2 +h2o C6H12O6+O2
C. origin of eukaryotes:-
The organisms having eukaryotic cells are called as eukaryotes. They were developed from prokaryotes. The first eukaryotes developed 2700million years ago. The free living eukaryotes were developed 1600 years ago. Evolution of eukaryotes proceeds fast due to the presence of free molecules of oxygen.
Cognogeny:-
It is the evolution of higher organism from lower organism by modifying characters.
It deals about the development of body structure, body system, modification of life etc.it helped to form developed eukaryotes. The eukaryotes changed themselves according to land, climate etc and formed diverse form of life.
Miller and Urey experiment:-
Stanley miller and herlod Urey did an experiment to test oparin and Haldane’s theory in 1953.they did following experiments:
They took mixture of gases (hydrogen, methane, ammonia, water vapour) in a closed gas chamber. They set the apparatus as shown in the figure.
They took boiling water in another closed liquid chamber. The mixture of gases resembles the gases of primitive earth and the hot water resembles the hot water of oceanic soup of primitive age.They supplied high voltage current i.e. 70000 volts through two electrodes in that glass chamber. The current supplied resembles the source of energy i.e. lightening at primitive earth. They left the apparatus for 2 weeks in lab. After 2 weeks they found that organic compounds were formed in the trap by the continuous reaction of gases. They synthesized amino acids, sugars and other compounds from the trap. Amino acids were glycine and alanine.
They found that organic compounds important for life were obtained from inorganic gases. They strongly supported oparin and Haldane’s theory that life was originated from non living chemicals.
Organic evolution:-
What is Evolution?
The formation of complex organisms through ‘change’ from simple ancestral types
Over the course of geological time.
According to the Theory of Organic Evolution
The various present day organisms were not created in the same form in which
they exist today, but have gradually evolved from much simple ancestral forms
of a common ancestor.
The characteristics of organism had been changing in the past; they are changing
even today, and will continue to do so in the future as well. This is due to the
fact that the environment in which organisms live also changes and organisms
need to be adapted to survive in the changed environment.
Many living organisms of the past have become extinct.
The origin of the various forms (species) found on earth has been a gradual
and extremely slow process, requiring hundreds or even thousands of years.
This process of slow and gradual change is called organic evolution.
Thus, the theory of organic evolution states that “All living things on earth
are here as a result of descent, with modifications from a common
Ancestor.
Types of organic evolution:-
Divergent:- it is a type of evolution in which different group of organisms or species evolve from a same common ancestor and occupied different places.
E.g. whale, bat, horse
Convergent:- it is a type of evolution in which different unrelated organism evolve from different ancestor but occupy same habitat.
E.g. whale, fish
Parallel:-it is a type of evolution in which different species of common ancestor occupy same evolutionary path.
E.g. new world porcupines and old world porcupines.
Progressive:-it is a type of evolution in which simple organisms developed toward complex organism.
E.g. Formation of multicellular organism from unicellular.
Retrogressive:-it is a type of evolution in which characters are gradually decreased from complex to simple.
E.g. parasites look simple but are more advanced.
Evidences of organic evolution
The evidences supporting organic evolution are derived from a number of fields
of Biology. Those discussed here are -
1. Morphological evidences
2. Embryological evidences
3. Paleontological evidences
4. Molecular evidences
1. Evidences from Morphology
Though organisms of different species and groups are quite different from each
other still they retain certain common features. Morphological evidences for
evolution are derived from -
(i) Homologous and analogous organs
(ii) Vestigial organs
(iii) Connecting links
The comparative study of various organs in different groups of vertebrates exhibit
common features which shows that they evolved from a common ancestor. Take
for example that of the heart of the vertebrates
(i) Homologous Organs
Homologous organs are the organs which are similar in structure and origin but
may look very different and perform different functions.
– Fore limbs of vertebrates are a good example of homologous organs. They are
built on the same fundamental plan yet they appear differently and perform
different function.
– In each case the fore-limb consists of humerus, radius and ulna, carpals,
metacarpals and phalanges. This basic similarity in the structure of the
apparently different fore limb of different kinds of vertebrates is due to the fact
that all these limbs have been evolved from a common type called the
pentadactyl (five-fingered) limb.
The homologous organs, therefore, prove that there has been evolution and not
creation.
(ii)Analogous organs
The structure which are functionally similar but structurally different are called
analogous organs.
The wing of an insect, and that of a bird or bat or pterodactyl are examples of
analogous organs . The function of the wing is the same (for flying) but
the insect wing has no structural resemblance with that of the vertebrates.
(a) Wing of insect (b) Wing of bird
(iii) Vestigial Organs
Vestigial organ is any small degenerate or imperfectly developed (non-functional)
organ or part which may have been complete and functional in some ancestor.
The only rational explanation for the presence of these non-functional organs is
That they are inherited from ancestors in which they were functional. shows
Some of the vestigial structures in human body.
Example of vestigial organ are nictitating membrane of human eye, molar teeth, appendix,pinnae etc.
(iv) Connecting Links
The animals or plants which possess
characters of two different groups of
organisms are known as connecting links.
The connecting links establish continuity
in the series of organisms by proving that
one group has evolved from the other. A
good example is that of a fossil bird
Archaeopteryx, which was a connecting
link between reptiles and birds. This bird
had a beak with teeth and a long tail (with
bones) like the lizards. It had feathers on
the wings and on the body like the birds.
Characteristics feature of archaeopteryx:-
It was the connecting link between reptilian and aves.it has intermediate characters of both.
It was found in the Jurassic period. It is known as lizard bird.
Body was covered with feather like apes and scales like reptile.
Fore limbs were modified into wings like bird and contain claws at top like reptile.
Head contain beak and teeth both.
Limbs were both for flying and climbing.
Contain long tail like reptile and covered with feather like bird.
2. Evidences from Embryology
Embryology is the study of development of an organism
The aspects of embryology which support the doctrine of organic evolution are :
similar stages of early development (morula, blastula or gastrula) in all the
animals;
the embryos of all vertebrates are similar in shape and structure in their early
stages.
This resemblance is so close that it is difficult to tell them apart
All the vertebrates start their life from a single cell, the zygote.
All of them during their life history, pass through two-layered blastula and three
layered gastrula stage and then through fish like stage with gill-slits.
All the different aspects of embryology strongly support the fact that the different
classes of vertebrates possess a common ancestry, and have differentiated from one
another through the process of evolution.
3. Evidences from Paleontology
Paleontology is the study of fossils. Fossils are the remains or traces of
animal and plant life of the past, found embedded in rock either as petrified
hard parts or as moulds, casts or tracks.
The fossils of the earliest era in the geological time scale were those of bacteria,
then invertebrates and then successively of fishes, amphibians, reptiles and lastly
of birds and mammals and among mammals primitive fossils of humans are the
most recent.
The fossils discovered provide the ancestral history of individual. Animals like
horse, camel etc. are direct proofs of organic evolution. This can be very well
illustrated by the past history of horse . The number of toes decreased
for greater speed, size gradually increased and teeth adapted to eat grass.
Importance of paleontology:-
It gives direct evidences of evolution.
It helps to know habit, habitat, behavior, feature of past or extinct organism.
It helps to find out the phylogeny of organisms.
Fossil of archaeopteryx is connecting link between bird and reptile.
It help to know the nutrition of past animals
It suggests that simple organism developed toward complex.
Types of fossils:-
Cast or mould: it is the hard covering of fossilized animal. If any organism die and gets preserved in clay or sediment, then clay or sediment becomes the cast or mould.
It helps to study external feature.
Amber: the fossil which is formed in resin or waxy substance of plant like pinus is known as amber. Mainly insects are preserved in resin.
Imprint: the sign or marks of ancient organism is known as impression or imprint.
Impression or imprint are found in clay or sediment. It is formed when the body decompose and only sign or mark is left.
Petrification: the fossil which is formed by the deposition of minerals in place of organic matter of organism is known as petrified fossils.
Compressed:-the fossil which are formed by the pressure of layer of earth is known as compressed fossil. If any organism is buried in lower layer of earth and preserved, then compressed fossil is formed.
4. Evidence of Evolution from biochemistry:
It gives the evidences of evolution, by the common similarities of chemicals in organism.
The common similarities are:-
Protoplasm: protoplasm is the physical basis of life. Protoplasm is made up of same basic elements in all organisms. The elements are water, carbohydrate, protein, fat, vitamin, minerals, enzymes etc.
Chromosome: it is the genetic material which carries characters from one generation to other generation. It is made up of nucleic acid and protein (histone and protamine). Basic component is same in all organisms.
Enzyme: enzyme is the bio-catalyst secreted by exocrine glands. Trypsin is the common enzyme from protozoa to mammal. Like wise amylase is the common enzyme from porifera to mammal.
Hormone: it is commonly called as chemical messenger. Hormones are secreted by endocrine gland. Thyroxin hormone is common in vertebrates. The activity of thyroxin hormone is same in all vertebrates.
Haemin crystal: when haemoglobin is added in acetic acid, then crystal is formed known as haemin crystal. If the shape and size of haemin crystal in two organism is same, then thy are closely related. If the shape and size of haemin crystal in two organisms is not same, then they are not closely related. Haemin crystal measures the degree of relationship between organisms.
Serum: the watery portion of the clotted blood is known as serum. The study of serum is known as serology. When the serum of closely related species is mixed, then it gives white precipitate. White ppt. is formed by the reaction of antigen and antibody.
Antigen: foreign protein in body e.g. virus, snake venom.
Antibody: chemical substance formed by body to fight with antigen.
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