(i) Shrews were the first mammals.
(ii) Lobefins are ancestors of modern day frog.
(iii) Homo habilis are first hominid, i.e. human-like individuals.
(iv) Homo erectus started using tools and fire.

Addition or deletion 1 or 2 chromosomes is aneuploidy (2n+1, 2n-2). Addition of 1 or more complete sets of chromosomes is polyploidy (3n, 4n).

1. Evolution is not a direct process in terms of determinism
2. As the environment changes, due to meteorological, biological and other physical activities, the organisms which are better adapted to the changed environment are selected by nature in a much lesser time scale.
3. It is also true for natural selection and evolution of antibiotic-resistant strains of bacteria in a time scale of months.
4. So, evolution is a stochastic process based on chance events in nature and chance mutation in the organism.

Darwin's theory had following drawbacks:
1. Survival of the fittest. Darwinism can explain the survival of fittest but is unable to account for arrival of the fittest. It is difficult to suppose that small variations could have formed organs like wings and mimicry colouration which are useful only in their fully developed state. Certain organs can be helpful to the organism only in fully developed state and what about their presence in early stages.
2. Over. specialization. Tusks of elephants and the antlers of some deer have overgrown their usefulness.
3. Vestigial organs. A number of vestigial organs persisting generation after generation has no explanation according to Darwinism.
4. Unchanged forms. Pteridophyte (Selaginella) is continuing on this earth for the last 200 million years
without any change, whereas, Darwin supposed addition of useful variations with every generation.
5. Darwin did not differentiate between somatic and germinal variations.
6. Darwin also failed to explain how land animal would evolve from aquatic animals.

The given equation represents Hardy-Weinberg's (genetic) equilibrium.
The principle states that allele frequencies in a population are stable and remain constant from generation to generation.
(a) The sum total of all the allelic frequencies is one.
Individual frequencies are named p and q, which represent the frequency of allele A and a, respectively, in a population of diploid organisms.
The frequency of AA individuals is p², while that of aa is q² and Aa is 2pq; hence p²+2pq+q²=1.
(b) When the frequency measured differs from the expected values, the difference indicates the extent of evolutionary change.
The disturbance in genetic equilibrium, would then be interpreted as resulting in evolution.

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.

(a) Any population has built in variation for every character.
Individuals with those characters which enable them to survive better in the given environment, would outbreed the others, who are less adapted. Fitness, according to Darwin, is reproductive fitness, i.e. individuals who are more fit in an environment leave more progeny than others.
These progenies survive better and more and more fit individuals are added to the population, i.e. natural selection.
The population thus comes to possess more fit individuals, i.e. nature selects the better fit invididuals and over a long period of time, through a number of generations, the population slowly becomes modified into a different form or a species, in the process called evolution, e.g. evolution of DDT-resistant mosquitoes.
(b) The two key concepts of Darwinian theory are:
(i) Branching descent.
(ii) Natural selection
(c) (i) Lemon thorn and Cucurbita tendrils are homologous-as both are stem modified.
(ii) Opuntia spines and pea tendrils are homologous-as both are leaf modifications.
(iii) Homologous organs are those organs in different groups of organisms, that are similar in basic structural and developmental patterns, but perform different functions and are superficially distinct.

(i) (b)
(ii) (b)
(iii) (a)
(iv) Connecting links establish continuity in the study of evolutionary progress made by organisms.
(v) (c)

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

A. Assertion and reason both are correct and reason is the correct explanation of Assertion.