In contrast to homologous organs, the analogous organs are different in their basic structure and developmental origin, but appear same and perform similar functions. 
(i) Wings of butterfly and birds
(ii) Eyes of Octopus and mammals.

Carolus Linnaeus, wise man, apes.

To move by swinging with arms from branches of trees as in apes.

Prosimians are the primitive primates, namely, lemurs and tarsiers. Simians are higher primates, viz, monkeys, apes and humans.

Some members of a population have traits (genes) which enable them to grow up and reproduce at a higher rate and leave more surviving offspring in the next generation than others.

The chromosomal aberrations and gene mutation are the only source of genetic variation in monoparental reproduction.

To pass on its genetic variation to its offspring and thereby to contribute its specific genes to the gene pool of the population.

Energy must have been provided in the form of heat, cosmic rays (including Uv-ray) and lighting.
Cyanobacteria are the organisms to release free-oxygen for the first time.

Life does not originate today because:
(i) The atmosphere of the present day is an oxidising one and any molecule synthesised is oxidised.
(ii) Other organisms devour any molecule formed.

Louis Pasteur showed that in pre-sterilised flasks, life did not come from boiled/killed yeast.
In another flask open to air, new organisms arose from killed yeast.
It showed that life arose only from pre-existing life.

Survival of the fittest means that those individuals which survive and reproduce successfully in their given environment or habitat, are called fit.
Such individuals produce more progeny (with more fit individuals), than the others who are less-adapted to survive and reproduce in that environment.

1.Fitness, according to Darwin, refers ultimately and only to reproductive fitness.
2.Those who are better fit in an environment would outbreed others, who are less fit in that environment; they leave more progeny (with more fit individuals) than others.
3.They will survive better and are selected by nature (natural selection) to reproduce and increase their population size.

Hardy-Weinberg principle states that allele frequencies in a population are stable and remain constant generation after generation; it is called genetic equilibrium.
Genetic drift
Genetic drift refers to the random changes in the allele frequencies of a population, in the allele frequencies of a population, that occur only by chance.
When the change in the allele frequency is so different in the original drifted population that it becomes a new species, the original population becomes founders and such an effect, is called founder effect.

Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other geographical areas (habitats).
Darwin's finches were the small black birds, which Darwin observed in Galapagos islands.
There were many varieties of these birds in the same island.
Darwin reasoned that after originated from a common ancestral seed-eating stock, the finches must have radiated to different geographical areas and undergone adaptive changes especially in their beaks, enabling some of them to become insectivorous.
Living in isolation for long, new kinds of finches must have evolved, which could survive in the new habitats.

Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other geographical areas (habitats).
Darwin's finches were the small black birds, which Darwin observed in Galapagos islands.
There were many varieties of these birds in the same island.
Darwin reasoned that after originated from a common ancestral seed-eating stock, the finches must have radiated to different geographical areas and undergone adaptive changes especially in their beaks, enabling some of them to become insectivorous.
Living in isolation for long, new kinds of finches must have evolved, which could survive in the new habitats.

1. Their forelimbs are the result of divergent evolution, i.e. the same structure developed along different directions due to adaptations to different needs.
2. Homology indicates common ancestry.
3. They are categorised as homologous organs.

Kinds of selections:
1. Stabilising selection
2. Directional selection
3. Disruptive selection.

The steps of chemical evolution are as follows:
(1) Origin of planets.
(2) Presence of elements.
(3) Interaction of elements to form inorganic compounds such as H ₂, H₂O,CO, HCN and CH. ₄.
(4) Formation of simple organic compounds such as sugars, amino acids, fatty acids, glycerol, purines and pyrimidines-as a result of interaction and energy from UV light and lightning. This as even well supported by Urey-Miller experiment.
(5) Simple organic molecules and even primitive inorganic molecules got dissolved and mixed in sea water.
(6) Formation of complex organic compounds. Amino acids joined to form polypeptides, and simple protein, simple sugars got converted into starches, fatty acids combined with glycerol to form fats and nucleotides joined to form nucleic acid.
(7) Formation of molecular aggregates was well supported by Sydney Fox and termed coacervates. Enzymes like substances were formed.
(8) These coacervates grow by absorbing molecules from surroundings and nucleic acid took control, turning  them into the first primitive living system
(9) Free genes diversified joined producing heterotrophs perhaps resembling viruses.
(10) Lipoproteinic membrane was formed around eobionts to form first living cells.
(11) Some of heterotrophs evolved further and became capable of making their own food by chemosynthesis and / or photosynthesis.
(12) First simple one called organisms were similar to today's cyanobacteria.

(1) Spontaneous generation refers to origin of life from non-living substances like mud, rocks, decaying matter under conditions that now exist on the earth, where as abiogenesis is the origin of life simple from non-living material under different set of conditions from those existed on the primitive earth.
(2) Theory of spontaneous generation was disapproved the finding. "life comes from pre-existing life". Francesco Redi (1668) placed throughly cooked meat in three jar
(i) uncovered
(ii) covered with parchment and
(iii) covered with muslin. Maggots developed only in the uncovered jar. No maggot developed in jar covered by parchment. Files visited the third jar produced maggots. Spallanzani (1765) boiled nutrition broth in glass flasks, sealed the flasks and kept them. The broth remained clear indefinitely with no signs of living beings.
Pasteur (1864) took broth in flasks having swan necks, boiled and allowed the broth to cool. No germs developed in the broth though it was connected with the atmosphere through curved necks of the flasks. The dirt particles could not reach the broth because they got trapped in the bend of the neck. When the swan necks were broken, broth developed colonies of microorganisms, showing that the same have come from air. The theory of biogenesis is, however, not applicable to origin of life.

Alexander I. Oparin (1894-1980), a Russian biochemist and J.B.S. Haldane (1892-1964), a British scientist have put forward the concept of biogenesis. According to Oparin and Haldane primeval earth had reducing condition and atmosphere is free from oxygen. Oxygen remained bound in HO and metallic oxides on the surface of rocks and its particles. The early gas cloud was rich in hydrogen, in form of methane (CH₄) and ammonia (NH₃) and water (H₂O). The organic nolucles formed due to atmospheric reaction accumulated slowly and gradually in sea and constitute what is called "Hot, dilute soup".
Significance of hot dilute soup. Thus conditions of reducing nature are unable to oxidize these organic compounds which form the basis of life.

Darwin's theory of Natural Selection was based on factual observations like:
(i) Natural resources are limited; so populations are stable in size except for seasonal fluctuations.
(ii) Members of a population show variation of every characteristic - no two members of a population are identical even though they show similarities.
(iii) Theoretically population size will grow exponentially, if everybody reproduced to the maximum capacity; it is seen in growing microbial/bacterial populations.
(iv) The population size in reality is limited -it is due to competition among individuals for resources and only those which are better adapted could survive and reproduce at the cost of others, who are less adapted to that habitat.
Darwin asserted that the heritable variations which make resource utilisation better in some individuals will enable them to reproduce and leave more progeny over a period of time; over many generations, there would be a change in the population characteristics, leading to origin of new species.