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The allele frequencies in a population are stable and are constant from generation to generation in the absence of gene flow, genetic drift, mutation, recombination and natural selection.

Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generation due to chance (sampling error). Genetic drift occurs in all population sizes, but its effects are strong in a small population. It may result in a loss of some alleles (including beneficial ones) and fixation of other alleles.

Genetic drift can have major effects, when the population is reduced in size by natural disaster due to bottle neck effect or when a small group of population splits from the main population to form a new colony due to founder’s effect.

(i) Actual remains is the most common method of fossilization. When marine animals die, their hard parts such as bones and shells, etc. are covered with sediments and are protected from further deterioration. They get preserved as such as they are preserved in vast ocean the salinity in them prevents decay. The sediments become hardened to form definite layers or strata. 

For example, Woolly Mammoth that lived 22 thousand years ago were preserved in the frozen coast of Siberia as such. Several human beings and animals living in die ancient city of Pompeii were preserved intact by volcanic ash which gushed out from Mount Vesuvius.

(ii) Petrifaction – When animals die the original portion of their body may be replaced molecule for molecule by minerals and the original substance being lost through disintegration. This method of fossilization is called petrifaction. The principle minerals involved in this type fossilization are iron pyrites, silica, calcium carbonate and bicarbonates of calcium and magnesium.

(iii) Natural moulds and casts – Even after disintegration, the body of an animal might leave indelible impression on the soft mud which later becomes hardened into stones. Such impressions are called moulds. The cavities of the moulds may get filled up by hard minerals and get fossilized, which are called casts. Hardened faecal matter termed as coprolites, occur as tiny pellets. Analysis of the coprolites enables us to understand the nature of diet, the prehistoric animals thrived.

Iron pyrites, silica, calcium carbonate and bicarbonates of calcium and magnesium.

Fossilization is the process by which plant and animal remains are preserved in sedimentary rocks. It is of three major types,

1. Actual remains 

2. Petrifaction 

3. Natural moulds and casts.

1. Mutuation theory was propounded by Hugo de Vries. 

2. Chemical theory of evolution was propounded by Oparin and Haldane

Relative dating is used to determine a fossil by comparing it to similar rocks and fossils of known age. Absolute dating is used to determine the precise age of a fossil by using radiometric dating to measure the decay of isotopes

Both the wings of cockroach and bird are different in structure but similar in their function. Thus, they are analogous structure that brings about convergent evolution.

They are similar in function. Thus we infer that these organs are analogous which has resulted in convergent evolution.

(i) The wings of a bird and the wings of a cockroach are analogous organs because these organs are used for flying 

(ii) They are different in structure. Each has evolved from a separate ancestral population as a means of more efficient mode of locomotion.

(a) Vertebrate hearts and (b) Thorns of Bougainvillaea and tendrils of cucurbits are homologous organs. They are similar in origin but different in function. They indicate common ancestry and divergent evolution.

The various parasitic adaptation enabling it to live in host are as follows : 

- Loss of unnecessary sense organs/ 

-  Adhesive organs or suckers to cling on to the host/ 

- Loss of digestive system/ 

- High reproductive capacity/ 

- Loss of chlorophyll and leave.

They represent divergent evolution as they have same fundamental structure, common ancestry but different functions.

Mode of interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter/one organism is benefitted, the other is harmed. 

e.g. Human liver fluke/Malarial parasite/Cuscuta.

Co-evolution is the relationship between two interacting organisms where both organisms failed to survive in the absence of the other. 

e.g. Fig and Fig wasp/ophrys and bumble bee.

Detailed Answer :

Parasitism it is the interaction between two species in which one species, called parasite depends for food & shelter on the other species called host and in this Process one species (parasite) is benefited while the other-the host is harmed or damaged e. g. tick & dog, fig. & fig & fig wasp.

Coevolution : When evolutionary changes is are species prompt the corresponding changes in other species with which the former interact, the phenomenon is called co-evolution, e,g host & pathogen, brey & predator etc. The parasites usually get host specific in such a way that both the hast & pathogen tend to co-evolve i.e. if the host develops the mechanism for resisting the parasite for its protection the pathogen also evolve the mechanism to counteract & neutralize them to succeed with the host species.

Organs with similar structure or same origin developed along different directions due to adaptation or different needs, to perform different functions are called homologous organs. 

For example, the fore limbs of some animals (Vertebrates) like whales, bats, cheetah and human have similar anatomical structure (i.e., humerus, radius, ulna, carpals, metacarpals and phalanges) develop differently to meet different need and to perform different functions.

Analogous structures are a result of convergent evolution because they are not anatomically similar structures though they perform similar function.

Detailed Answer: 

Analogous structures are said to be the result of convergent evolution because, though they perform similar function but are different in their structural details and origin e.g. wing of insects, birds and bats like unrelated organisms.

Sweet potato tuber is a root modification, and potato tuber is a stem modification but they show convergent evolution because both of them are unrelated and perform the functions similar of storage of food and vegetative reproduction.

The eggs of the parasitic bird (Koel) resemble the host's egg (Crow) in size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them out from the nest.

Organs with similar structure / same ancestry / anatomically same/ same origin developed along different directions due to adaptation / different needs. to perform different functions. 

For example the fore limbs of some animals (Vertebrates) like whales, bats, cheetah and human have similar anatomical structure (i.e. humerus, radius, ulna, carpals,metacarpals and phalanges) develop differently to meet different needs / to perform different functions.

Detailed Answer:

Homologous organs are the organs having fundamental similarity in structure and origin but different function. They represent a case of divergent evolution. Divergent evolution is the process by which related species become less similar in order to survive and adapt in different environmental condition. 

For example, human hand, Whale's flippers, Bat's wing, and Cheetah's foot. All these perform different function, but are constructed on the same plan. Thus, in these animals, the same structure developed along different directions due to adaptations to different needs.

The term biogenesis refers to the production of life from already-living matter or organisms. This is in contrast to abiogenesis, which refers to the production of life from non-living matter. Natural abiogenesis has never been observed, nor are there any generally accepted models for how it could occur. Biogenesis, on the other hand, is routinely observed at all levels of life. When a bacteria divides, a plant produces seeds, or a mammal gives birth, biogenesis is occurring.