They want to know whether the organisms on other planets, if any, are similar, have similar genetic code and similar elements to ours or different.

The concept of biogenesis means that new life at present comes only from preexisting life (Omne vivum exvivo).

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.

convergent evolution is the evolutionary process, where anatomically different structures in different groups of organisms evolve towards the same function, in similar habitats.
Such structures in different groups of organisms which perform similar function, but are anatomically different, are called analogous organs.
The wings of a butterfly and those of bird are anatomically different, but perform the same function (flying); hence they are said to be analogous organs.

1. Theory of special creation,
2. Theory os spontaneous generation.
3. Theory of catastrophism.
4. Interplanetary theory,
5. Theory of Eternity of life
6. Modern or chemical or naturalistic theory.

1. We are still not clear whether evolution and natural selection are processes or results of some unknown processes.
2. On one hand, when we describe the world as we see today, we describe evolution a process.
3. On the other hand, when we describe life on earth, we treat evolution as a consequences of the process of natural selection.

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.

(a) 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.
(b) 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) Hardy-Weinberg's principle says that allele frequencies in a population are stable and constant
from generation to generation. The gene pool remains constant. This is called genetic equilibrium.
Sum total of all the allelic frequencies is 1. Individual frequencies, e.g., can be named p, q, etc.
Natural selection disturbs the allelic frequencies. Through natural selection either the frequency of
p increases or the frequency of q it will disturb the natural frequency. In a diploid, p and q represent the frequency of allele A and allele a. 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 the product of the probabilities.
Hence, p² + 2pq + p² = 1
The factors that affect the Hardy-weinberg's equilibrium are :
(i) Migration
(ii) Gene flow
(ill) Genetic drift
(iv) Mutation
(v) Genetic recombination
(b) Variation due to mutation or recombination during gametogenesis or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation. Natural selection can lead to stabilization (in which more individuals acquire mean character value), directional change (more individuals acquire value other than the mean character value) or disruption (more individuals acquire peripheral character value at both ends of the distribution curve).

(i) Actually, the child is normal and carries the vestigial organ, i.e., remnant of last vertebra.
(ii) It refers to the reappearance of structures that were dominant in our remote ancestors.
(iii) As a good citizen and a biology student, I will educate people about vestigial organs and phenomenon of atavism so that they stop believing in myths.

(a) Dryopithecus and Ramapithecus:
Characteristics:
(i) They were hairy.
(ii) They walked like gorillas and chimpanzees.
(iii) Ramapithecus was more man-like while Dryopithecus was more ape-like.
(b) (i) East African grasslands.
(ii) Homo habilis, Homo erectus and Neanderthals had brain capacities of 650-800 cc, 900 cc and 1400 cc, respectively.
(iii) During the ice age between 75,000-10,000 years ago.