ORIGIN OF LIFE
•The origin of life is a unique event in the
history of universe.
•The Big bang theory explains that the
universe arose from a huge explosion .
•The earth was supposed to have been
formed about 4.5 billion years before, in
the solar system of the milky way.
•Life started appearing about 500 million
years after the formation of earth.
THEORIES OF ORIGIN OF
LIFE
•Theory of special creation.
•Theory of Panspermia.
•Theory of spontaneous generation
•Theory of chemical evolution.
•The theory of chemical evolution is widely accepted.
Theory of Chemical Evolution
•This theory was proposed by OPARIN and
HALDANE.
•They proposed that the first life form could have
come from the pre existing , non –living organic
molecules and that formation of life was preced by
chemical evolution,
•The conditions on earth that favoured were very
high temp, volcanic storms, reducing
atmospherethat contained methane ammonia, water
vapour
EXPERIMENTAL PROOF
•Stanley miller and Urey created conditions similar to the
primitive atmosphere in the laboratory using glass apparatus and
tubes.
•They created electric charges using electrodes.in a flask
containing methane , ammonia, hydrogen and water vapour at
8000C
•The water –containing chamber was heated to provide water
vapour
•After a week, they observed the formation of a number of
complex organic molecules like some sugars, nitrogen bases,
amino acids and lipids.
•Thus the chemical evolution of life was more or less accepted.
Image
condenser
Stop
cock
Water containing
organic compounds
Origin of first cell
The first non cellular forms of life could have originated three
billion years ago
They would have been giant molecule like RNA, proteins, or
polysaccharides
These capsules were able to replicate
The first cellular forms must have appeared about less than two
billion years ago
all life forms appeared in water bodies
Once formed the single cell must have evolved into the diverse
complex forms
EVOLUTION
•The word evolution ( L.evolviere) means to unfold the hidden
potentialities
•Biological evolution refers to the changes in the properties of
organisms over a number of generations
•It is the process of cumulative change of living populations
•Palaeontology
•Comparative anatomy and morphology
•Embryological
Palaentology
Fossils found in the rocks support organic evolution
Rocks are formed by sedimentation and across section of the
earth’s crust indicates the arrangement of the sediments one
over the other during the long history of earth
Different sediments contain different life forms which
probably died during the formation of the particular sediment
Certain organisms have become extinct
Those found towards the upper layers resemble modren
organism
Some forms are seen only for certain periods
The evidence for evolution has primarily come from four
sources:
1.
the fossil record of change in earlier species
2.
the chemical and anatomical similarities of related life
forms
3.
the geographic distribution of related species
4.
the recorded genetic changes in living organisms over
many generations
Comparative anatomy and
morphology
Homolgy :- It is the relationship among organs of different groups of
organisms that show similarity in the basic structure and embronic
development, but perform different functions
Eg:- fore limbs of whales, bat, birds, amphibians, and man
Among plants the thorn of bougainvilla and tendrils of Cucurbita
Analogy
Analogy is the relationship among organs of different groups of
organisms performing the same function, irrespective of structural
differences
Eg;- Eyes of octopus and mammals
Wings of butterfly and those of birds
Flippers of whales and those of penguins
tubers of potato and tubers of sweet potato
Analogy is the result of convergent evolution AND
homology is the result of divergent evolution
Molecular homology
It refers to the similarities in the biomolecules of different groups
of organisms It points to the same common ancestry of divergent
evolution
•Based on his observations , he concluded
•Charles Darwin made a sea voyage round the
world in a sail ship H.M.S. Beagle
1)The existing living organisms share similarities to varying
degrees not only among themselves but also with the life forms
that existed millions of years ago
2) There has been a gradual evolution of life forms
3) Any population has built in variation in characteristics
4) Individuals with those characteristics which enable them to
survive better in natural conditions , would outnumber the
others, who are less adapted under the same natural conditions
Charles Darwin & his Sail Ship Beagle
•This fitness of individual according to Darwin isreproductive
fitness
•Such fit individuals leave more progeny
•They are selected by nature( natural selection
•In due course of time , new life forms will arise and evolve
•Darwin considered natural selection as a mechanism of
evolution
•Alfred Wallace , a naturalist who worked in Malay Archipalago
had also arrived at similar conclusions at about the same time
Examples for Natural Selection
Industrial Melanism
Many species of moths in the
British Isles began to become darker
in color in the 19th century.
The best-studied example is the
peppered moth, Biston betularia.
The moth flies at night and rests by day on tree trunks. In areas far from
industrial activity, the trunks of trees are encrusted with lichens. As the,
the light form (circled in red) is practically invisible against this
background.
In areas where air pollution is severe, the combination of toxic gases and
soot has killed the lichens and blackened the trunks. Against such a
background, the light form stands out sharply.
The moth is preyed upon by birds that pluck it from its resting place by
day. In polluted woods, the dark form has a much better chance of
surviving undetected. When the English geneticist H. B. D. Kettlewell ()
released moths of both types in the woods, he observed that birds did,
indeed, eat a much higher fraction of the light moths he released than of
the dark.
The moth gets its name from the scattered dark markings on
its wings and body.
In 1849, a coal-black mutant was found near Manchester,
England. Within a century, this black form had increased to
90% of the population in this region
.
Resistance to chemicals
•Use of pesticides/ insecticides has in resistant varieties
of organisms in a less time eg;- DDT resistance in
mosquitoes
•It is also true with microbes , many antibiotic – resistant
varieties of disease causing bacteria are preparing in a
very short period
•This shows that evolution is not a direct process but that
is based on chance events in nature and mutation in the
organisms
ADAPTIVE RADIATION
It is an evolutionary process in which an ancestral stock gives rise to
new species adapted to new habitats and new way of life.
eg:- Darwin’s Finches of Galapagos
These were small black birds which Darwin
observed in Galapagos Island
He reasoned that after originating from acommon
ancestral seed- eating stock, the finches have
radiated to different geographical regions and
undergone adaptive changes especially in the type of
beak
Living in isolation for long , new kinds of finches
emerged
Australian Marsupials
A number of Marsupials evolved from an ancestral stock
within Australia
When more than one adaptive radiation appeared to have
occurred in an isolated geographical area with different
habitat , it can be called as convergent evolution
The two key concepts of Darwin’s theory of evolution are
Branching Descent and natural selection
Tansmanian wolf
Sugar glider
Tiger
Rat
mole
Marsupials
Banded
ant eater
koala
Bandicoot
Marsupial rat
Wombb
at
kangaroo
Lamark’s theory of Evolution
The evolution of life forms had occurred by the use and disuse
of organs
The characters acquired are passed through generations after
generations
Eg;- long neck of giraffe
This principle states that under certain conditions of stability , the
allele frequencies of a population are stable and remain constant from
generation to generation in sexually reproducing organism
This stability is is called genetic equilibrium or Hardy –Weinberg
equilibrium
Disturbance in the genetic equilibrium is considered as evolutionary
change
Five factors affect Hardy-Weinberg equilibrium
Gene Migration
4) Recombinations
2) Genetic drift
5) Natural selection
3) Mutations
Natural selection on single-gene traits can lead to changes in
allele frequency and thus to evolution.
Brown: autosomal
dominant
ie. Plumage coloration in turkeys:
Black: autosomal recessive
Organisms of one color may produce fewer offspring than organisms of
another color because they might be more visible to predators and less
likely to survive and reproduce.
However, when traits are controlled by more than one gene, such as in
polygenic traits, the effects of natural selection become more complex.
Natural selection can affect the distribution of phenotypes in any of three
ways: directional selection, stabilizing selection, or disruptive selection
Peaks gets higher
and narrow
Peaks shift to one
direction
stabilising
dircetional
Effects of natural selection
Natural selection can affect the
distribution of phenotypes in any
of three ways: directional
selection, stabilizing selection,
or disruptive selection.
Evolution of horse
•The ancestor of horse that lived in Eocene epoc was
Eohippus
•It evolved into Mesohippus(oligocene),
Merihippus(miocene), and Equus( pleiocene)
•The major evolutionary changes included
•Lengthening of limbs
•Progressive reduction in the number of toes
•General increase in body size
•And enlargement of brain size
EVOLUTION OF MAN
The common ancestor of man and ape is a primate DRYOPITHECUS
that lived 15 million years ago
•
The next stage in the hominid evolution is RAMAPITHECUS
•
Both are hairy and walk like gorillas and chimpanzees
•
Ramapithecus are more man like
•
Human evolution has the following stages
1) Australopithecus
2) Homo habilis
3) Homo erectus
4) Homo sapiens
5) Homosapeins sapeins