Molecular homology: Similarities of organisms at molecular level.
Examples:
1.Resemblances of blood group.
2. Blood proteins.

Urey and Miller conducted experiment which supported that life originated by chemosynthesis.The chemosynthetic theory states that life orginated from non-living matter is bases on tyhe presence of methane and ammonia in the atmosphere. It required a high temperature, high energy radiations and electric discharges.    

Formation of first living cell: The fluid substances in colloidal substances formed small globules called coacervates. They got enveloped by lipid membrane. A coacervate having nucleoproteins in the middle surrounded by various nutritive substances ensheathed by a protective membrane was fore-runner of a simple type of call. It was called eobiont or protocell. Gradually inclusion and organelles were formed by combination of various macromolecules. Finnaly a cell was formed.

Role of sum in origin and evolution of life. Sun, The ultimate source of energy for the living world on this plant has played a significant role in the origin and evolution of life.
1. Influence of high energy radiations from sun: The simple elements such as carbon, oxygen, hydrogen and nitrogen combined to form complex molecules of organic compounds under the influence of high energy radiations from the sun.
2. Formation of chlorophyll: The earlier organism present at the earth were heterotrophs, as the chemical evolution proceede and omplex macromolecules joined with each other. The chlorophyll was formed and the organisms became autotrophs and started manufacturing their own organic food.
3. Solar energy: Solar energy is the only source of energy in the living world. Sun has played a vital role in the chemical evolution.

Fossils of Dinosaurs have been unearthed to reveal evolution of reptiles in Jurassic period. It further led to the evolution of birds and mammals. Recently, fossils of shark-toothed reptiles from Sahara deserts have been discovered. Fossils of flying birds with teeth in the jaws has been discovered.

(a) The variations in the beaks are adaptations to their food habit fresh- eating, insectivorous or seed/ fruit-eating.
(b) Darwin conjectured that all the varieties must have evolved on the same island itself.
From the original seed-eating features, other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
This process of evolution of different species in a given geographical area, starting from a point and literally radiating to other geographical areas, is called adaptive radiation.

(i) Invertebrates  - 500 million years ago
(ii) Jawless fish  - 350 million years ago
(iii) Sea weeds   - 320 million years ago

Adaptive radiation is the evolutionary process in which a common ancestor evolves into a number of species, in a given geographical area, starting from a point and literally radiating to other areas of geography.
A number of Australian marsupials, each different from the other, evolved from an ancestral stock, all within the Australian island continent.
When more than one adaptive radiation appeared to have occurred in an isolated geographical area, representing different habitats, it can be called convergent evolution.
Placental mammals of Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals, each of which appears to be 'similar' to a corresponding marsupial, e.g. Bob cat resembles Tasmanian tiger cat.
Lemur - Spotted cuscus.
 Anteater - Numbat.

Convergent evolution:
It is the evolutionary process in which anatomically different organs in different groups of organisms, evolve towards the same function.
Analogous organs are the result of convergent evolution, e.g. Sweet potato (root modification) and potato (stem modification) are analogous, as they both are tuberous with stored food materials.
Divergent evolution:
It is the evolutionary process in which the same structure develops in different directions in different groups of organisms as adaptations to different needs.
Homologous organs are the result of divergent evolution, e.g. human hands are homologous to the wings of a bird, as their basic structure (number and types of bones) is similar. 

(i) Branching descent:
1. The members of a population show variations in their characteristics, though they look superficially similar.
2. Some individuals/organisms are better adapted to survive in the given environment.
3. This adaptive ability is inherited and has a genetic basis.
4. Accumulation of variations over a period of time through a number of generations leads to a change in the population characteristics, i.e. descent with modification.
(ii) Natural Selection:
1. Natural selects those individuals who are fit in the environment.
2. Fitness, according to Darwin, refers to ultimately and only - reproductive fitness.
3. Those individuals who are better adapted, reproduce in large number and the progeny consists of more fit individuals, who are selected by nature, i.e. natural selection.

Theory of chemical evolution or abiogenesis was proposed by Oparin and Haldane.
It states that the first form of life could have come from pre-existing non-living organic molecules (like RNA, proteins, etc.) and that formation of life was preceded by chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents.
Miller's experiment:
He created conditions similar to the primitive earth in the laboratory.
Electric discharge was produced (by using electrons) in a closed flask, containing methane, hydrogen, ammonia and water vapour.
The temperature was kept at \(800\)\(^{ \circ }{ C }\). 
 After a week, he observed formation of amino acids.
Such molecules must have reacted among themselves to form giant, self-replicating molecules, the first form of life.

1.Anthropogenic actions, i.e. human activities have been found to enhance evolution.
e,g. 1.Use of DDT has resulted in evolution of DDT-resistant mosquitoes.
2.Evolution of antibiotic or drug-resistant microbes.
3. When DDT was used fo the first time, many mosquitoes died, but a few survived.
4. These few mosquitoes showed resistance to DDT and reproduced in the presence of DDT.
5. Most of the offspring were also resistant to DDT.
6. Hence, the mosquito populations of today consist mainly of DDT-resistant mosquitoes and hence, DDT is not effective.
7. In the absence of DDT, these DDT-resistant mosquitoes had no advantage over those mosquitoes, which were sensitive to DDT.
8. This is an example of evolution due to anthropogenic activities.

1. Lobefins are the fish with stout and strong fins, that could move on land and go back to water; they must have lived about 350 mya and were thought to be extinct.
2. In 1938, a Coelacanth (lobefin) was caught in South Africa.
3. Though no specimens of these are left with us, they evolved into the first amphibians.
4. These were the ancestors of modern-day frogs and salamanders.