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

Stop cock

Water containing organic compounds

condenser

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

AnalogyAnalogy 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 RADIATIONIt 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

Marsupials

Tiger Rat

Banded ant eater

Marsupial ratkangarooWomb

bat

Bandicoot

koala

mole

Sugar glider

Tansmanian wolf

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. ie. Plumage coloration in turkeys:  Black: autosomal recessive

Brown: autosomal dominant                                                                                                                                                                                                                                        

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.

stabilisingdircetional

Peaks shift to one direction

Peaks gets higher and narrow

Natural selection can affect the distribution of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection.

Effects of natural 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 MANThe 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