ORIGIN OF LIFE
The origin of life is a unique event in the history of universe.
The universe is vast.
The universe is very almost 20 billion years old.
Huge clusters of galaxies comprise the universe.
Galaxies contain stars and clouds of gas and dust.
The Big Bang theory explains the singular huge explosion unimaginable in physical terms.
The universe expanded and hence, the temperature came down.
The gases condensed under gravitation and formed the galaxies of the present day universe.
In the solar system of the milky way galaxy, earth was supposed to have formed about 4.5 billion years back.
There was no atmosphere on early earth.
Water vapour, methane, carbondioxide and ammonia released from molten mass covered the surface.
The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped.
Oxygen combined with ammonia and methane to form water, CO2 and others.
The ozone layer was formed.
As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.
Louis Pasteur experimentation demonstrated that life comes only from pre-existing life.
He showed that in pre-sterilised flasks, life did not come from killed yeast
while in another flask open to air, new living organisms arose from ‘killed yeast’.
Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.)
and that formation of life was preceded by chemical evolution,
i.e., formation of diverse organic molecules from inorganic constituents.
The conditions on earth were high temperature, volcanic storms, reducing atmosphere containing CH4, NH3, etc.
In 1953, S.L. Miller, an American scientist created electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 8000C.
He observed formation of amino acids.
In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.
Analysis of meteorite content also revealed similar compounds
indicating that similar processes are occurring elsewhere in space.
The first non-cellular forms of life could have originated 3 billion years back.
They would have been giant molecules (RNA, Protein, Polysaccharides, etc.).
These capsules reproduced their molecules perhaps.
The first cellular form of life did not originate till about 2000 million years ago.
These were probably single-cells.
All life forms were in water environment only.
The first form of life arose slowly through evolutionary forces from non-living molecules is
accepted by majority.
Theories of Evolution
Concept of Conventional religious literature
The theory of special creation and has three connotations.
1.All living organisms (species or types) were created as such.
2. Diversity was always the same since creation and will be the same in future also.
3. The earth is about 4000 years old.
But, during the observations made during a sea voyage in a sail ship called H.M.S. Beagle
round the world, Charles Darwin concluded that existing living forms share
similarities to varying degrees not only among themselves but also with
life forms that existed millions of years ago.
Many such life forms do not exist any more.
Also, during the different periods of histroy on earth, there had been extinctions of different life forms in the earth.
There is a gradual evolution of life forms.
Those characteristics which enables to survive better in natural conditions (climate, food, physical factors, etc.)
would outbreed others that are less capable to survive under such natural conditions.
The other term is the "Fitness".
According to Darwin, "Fitness" refers ultimately and only to reproductive fitness.
So, those who are better fit in an environment, leave more progeny than others.
And hence will survive more and are selected by nature.
Darwin termed it as natural selection and implied it as a mechanism of evolution.
EVIDENCES FOR EVOLUTION
Proof of Evidence that evolution of life forms has taken place
1. Paleontological evidence:
Dfferent aged rock sediments contain fossils of different life forms that probably died during the formation of particular sediment.
Fossils are remains of hard parts of life-forms found in rocks.
The study showed that different form varied over time and certain life forms are restricted geological time span.
Hence, new forms of life have arisen at different times in history of earth.
2. Homologous organs:
Those organs that perform different function but have similar origin and structure are called homologous organs.
For example human, cheetah, bat and whales share similarities in pattern of bones of forelimbs although
these forelimbs perform different functions in these animals.
In these animal similar structure developed along different directions due to adaptation of different needs.
This is called divergent evolution.
3. Analogous structures:
They are not anatomically similar organs but perform similar function.
For example eyes of mammals and octopus or flippers of penguin and dolphins.
This is due to similar habitat that resulted in similar adaptive features in different groups of organisms.
This that of evolution is called convergent evolution.
From above notes we can determine the difference between Homologous structures & Analogous structures as ;
Here for the sake of simplicity we will choose;
HS = Homologous Structure
AS = Analogous Structure
a. HS are similar in anatomy whereas AS are dissimilar in anatomy.
b. HS does dissimilar functions whereas AS do similar functions.
c. HS are developed in related animals whereas AS are developed in unrelated animals.
d. HS are Inherited from a common ancestor but AS are not inherited from common ancestor.
e. HS shows similar developmental pattern but developmental pattern is not similar in AS.
f. HS are similar in structure and origin whereas AS dissimilar in structure and origin
4. Biochemical evidences:
Similarities in proteins and genes performing a given function among diverse organisms give hints to common ancestry.
These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms.
Now, let's see the difference between convergent and divergent evolution.
1. Development of different functional structures from a common ancestral form is called divergent evolution whereas
development of similar adaptive functional structures in unrelated groups of organisms is called convergent evolution.
2. Homologous organs show divergent evolution but Analogous organs show convergent evolution.
Examples of divergent evolution are Darwin’s Finches, Australian Marsupials, locomotion in mammals whereas
examples of convergent are Australian Marsupials and Placental mammals,
various equatic vertebrate and wings of insect bird and bat.
Evolution by Natural Selection
Evolution by Natural Selection
A case of natural selection was seen in England in 1850s, i.e., before industrialization in a peppered moth (Biston betularia).
This moth had two forms: grey colour and black colour (Carbonaria).
In the early part of the nineteenth century , before industrialization only the grey coloured forms of moths were present;
the dark forms were rare.
The grey coloured moths were seen on the tree trunks covered with lichens and so they were able to escape from their enemies.
Later on in 1920, due to the development of industries, post industrialization,
the lichens were killed and the tree trunks looked dark due to the deposition of industrial soot.
Birds, now were able to spot these moths and feed upon them.
So the grey coloured moths were eaten by the birds and the dark coloured moths escaped from the birds.
Then now the coal is replaced by the industries and oil and electricity is used.
This has reduced the soot production and ultimately less deposition of soot on the tree trunks.
These tree trunks have, now, again become grey in colour.
Consequently, grey coloured moths have again increased in number.
This example clearly shows the action of natural selection.
Evolution by anthropogenic action
Resistance of mosquitoes to pesticides.
When DDT was introduced to control mosquitoes it was tremendously successful.
Most of the mosquitoes were sensitive to DDT and were therefore killed.
In that population of mosquitoes, few mosquitoes became resistant to DDT and survived.
They multiplied and now almost total population of mosquitoes became resistant to DDT.
Same pattern has been observed in bacteria which are multidrug resistant due to excess use of drugs and medicines.
Adaptive Radiation
The process of evolution of different species in given geographical area starting from a point and radiating
to other areas of geography (habitat) is called adaptive radiation.
Darwin’s finches represent one of the best examples of adaptive radiation.
Australian marsupials, each with different from other evolved from one ancestral stock,
but all within Australian island continents.
When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats),
this is called as convergent evolution e.g Placental mammals and Australian marsupials.
Biological Evolution
The nature select for fittest and fitness is based on characteristics which are inherited.
Some organisms are better adopted to survive in otherwise hostile environment.
Fitness is the end result of the ability to adopt and get selected by nature.
Lamarck had said that evolution of life form had occurred but driven by use and disuse of organs.
He gave the example of giraffe to evolve their neck by foraging leaves on tall trees
and had to adapt by elongation of their necks.
Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.
Darwin theory of natural selection was based on certain observations like;
a.Limited natural resources.
b.Over population
c.Competition for resources
d. Struggle for existence
e. Survival of the fittest.
Mechanism of Evolution
Hugo deVries based on his work on evening primrose brought forth the idea of mutation.
Mutation is the large difference arising suddenly in a population.
Mutations are random and directionless while Darwin variations are small and directional.
Hugo deVries believed that mutation causes speciation and hence called saltation (single step large mutation).
Difference between Lamarckism, Darwinism and Mutation Theory
Hardy- Weinberg Principle
In a given population, frequency of occurrence of alleles or genes can be find out.
These frequencies remains fixed and even remain the same through generation.
This fact was represented by Hardy-Weinberg principles using algebraic equation.
This principle states that allele frequencies in a population are stable and is constant from generation to generation.
The gene pool remains constant.
This is called genetic equilibrium and sum total of all the allelic frequencies is 1.
Binomial expansion of (p+q)2 = p2+2pq+q2=1
where p and q represent the frequency of allele A and allele a in a population.
The frequency of AA individuals in a population is simply p2.
This is simply stated in another ways, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes
of a diploid individual is simply the product of the probabilities, i.e., p2.
Similarly of aa is q2 , of Aa 2pq.
Hence, p2+2pq+q2=1.
When frequency is measured, the actual value varies that indicates the extent of evolutionary changes.
Change of frequency in a alleles (Hardy-Weinberg equilibrium) in a population resulted due to evolution.
The factors that affect Hardy-Weinberg equilibrium are;
a. Gene migration or gene flow.
b. Genetic drift
c. Mutation
d. Genetic recombination
During genetic drift, sometimes change in alleles frequency is so different in a sample of population that they become a different species.
The original drifted population becomes founder and that effect is called founder effect.
Brief Account of evolution
About 2000 million ago first cellular form of life appeared on earth.
Slowly single-celled organisms became multi-cellular forms and by the time 500 mya, invertebrates were formed and active.
Jawless fish evolved around 350 mya.
Organisms started to invade from water to land.
Fish with stout and strong fins could move on land and go back to water.
These animals called lobefins evolved into the first amphibians.
Later, these amphibians evolved into reptiles.
They lay shelled eggs.
Then reptiles of different shapes and sizes dominated on earth , fish like reptiles e.g. Ichthyosaurs and the land reptiles e.g dinosaurs.
The biggest of them was Tyrannosaurus rex.
Some of the reptiles evolved into birds and later some of them to mammals.
Mammals were viviparous and more intelligent in sensing and avoiding danger .
ORIGIN AND EVOLUTION OF MAN
About 15 mya, primates called Dryopithecus and Ramapithecus were existing.
They were hairy and walked like gorillas and chimpanzees.
Ramapithecus was more man-like while Dryopithecus was more ape-like.
Few fossils of man-like bones have been discovered in Ethiopia and Tanzania
and these revealed hominid features leading to the belief that about 3-4 mya, man-like primates walked in eastern Africa.
They were probably not taller than 4 feet but walked up right.
Two mya, Australopithecines probably lived in East African grasslands.
Evidence shows they hunted with stone weapons but essentially ate fruit.
Some of the bones among the bones discovered were different.
This creature was called the first human-like being the hominid and was called Homo habilis.
The brain capacities were between 650-800cc.
They probably did not eat meat.
Fossils discovered in Java in 1891 revealed the next stage,
i.e., Homo erectus about 1.5 mya.
Homo erectus had a large brain around 900cc.
Homo erectus probably ate meat.
The Neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000-40,000 years back.
They used hides to protect their body and buried their dead.
Homo sapiens arose in Africa and moved across continents and developed into distinct races.
During ice age between 75,000-10,000 years ago modern Homo sapiens arose.
Pre-historic cave art developed about 18,000 years ago.
Agriculture came around 10,000 years back and human settlements started.
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