Human appendix is the remnant of caecum which is functional in the digestive tract of herbivorous animals like rabbit. Cellulose digestion takes place in the caecum of these animals. Due to change in the diet containing less cellulose, caecum in human became functionless and is reduced to a vennifonn appendix, which is vestigial.

The thorn of Bougainvillea and the tendrils of Curcurbita and Pisum sativum represent homology. The thorn in former is used as a defense mechanism from grazing animals and the tendrils of latter is used as a support for climbing.

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.

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.

Mesozoic era is divided into three periods namely Triassic, Jurassic and Cretaceous.
Dominating Fauna: Reptiles and Dinosaurs
Dominating Flora: Conifers, Ferns and Ginkgon.

It is the study of prehistoric life through fossils

Hardened faecal matter are termed coprolites and occurs as tiny pellets. Analysis of coprolites enables us to understand the nature of the diet, on which the prehistoric animals thrived.

They argued that external conditions stimulate the somatic cells to produce certain 'secretions' which reach the sex cells through the blood and bring about variations in the offspring.

Ernst Von Haeckel propounded the "biogenetic law or theory of recapitulation" which states that the life history of an individual (ontogeny) briefly repeats or recapitulates the evolutionary history of the race (phylogeny). In other words "Ontogeny recapitulates Phylogeny".

Sudden appearance of vestigial organs in highly evolved organisms is called atavistic organs. Eg: presence of tail in a human baby is an atavistic organ.

(i) Darwin failed to explain the mechanism of variation.
(ii) Darwinism explains the survival of the fittest but not the arrival of the fittest.
(iii) He focused on small fluctuating variations that are mostly non-heritable.
(iv) He did not distinguish between somatic and germinal variations.
(v) He could not explain the occurrence of vestigial organs, over specialization of some organs like large tusks in extinct mammoths, oversized antlers in the extinct Irish deer, etc.,

Methane, carbondioxide, ammonia and water vapour.

1. There are five basic processes that affect the Hardy-Weinberg equilibrium and cause variations at genetic level.
2. These include (i) Mutation (ii) recombination (iii) Gene migration (iv) Genetic drift and (v) natural selection.
3. Among the above five processes, lets discuss how mutation, natural selection and genetic drift affect Hardy Weinberg equilibrium.
(a) Mutation:
1. Mutation are sudden heritable changes in the characteristics of the organisms.
2. These mutations are random (indiscriminate) with respect to the adoptive needs of organisms.
3. Most mutations are harmful or with no effects (neutral) on their bearers.
4. However under changed environmental conditions, the alleles, which were previously harmful or neutral may become advantageous.
5. The rate of mutation is very slow usually one mutation occurs in a million still these mutation rates are sufficient to create considerable genetic variation.
6. Mutations help in maintaining variations within population.
7. Mutation also introduce new genes and alleles into the gene pool (sum total of all genotypes or alleles found in a population).
8. It is the gene pool in which new genes are added or removed. This variability of genes (or) alleles in a gene pool, then serve as a raw material for evolutionary changes.
9. The accumulation of many mutations over hundreds of generation cause large scale changes.
(b) Natural selection
1. Natural selection is the most important evolutionary process that brings about changes in allele frequencies.
Definition
1. The process of differential reproduction that lead to differential contribution of genotypes to the gene pool of the next generation.
2. Natural selection results a change in allele frequencies of a population.
(c) Genetic drift
1. It refers to the elimination of certain genes in a small isolated population either due to intensive inbreeding causing permanent fixation of some genes or death of a small section of population by natural calamity.
Definition
1. The random changes in the allele frequency occurring by chance alone are called genetic drift.
2. This means that the alleles that form the gene pool of the next generation are a sample of the allele from current generation.
3. Sampling errors (chances) often lead to the elimination of certain alleles and fixation by others thus reducing the genetic variability of the population.
4. The effect of genetic drift is very small in large but can be large in a small population.
5. Thus these forces that change the allele and genotypic frequencies in a population and so called evolutionary agents.
6. As long as Hardy-Weinberg Equilibrium remains constant the evolution cannot occur since the genetic equilibrium is a sort of inertia whose tendency is rather conservative. Evolution become possible only if the inertia is overcome or the equilibrium is broken.

Fossilization is the process by which plant and animal remains are preserved in sedimentary rocks. They fall under three main categories.
(i) Actual remains
The original hard parts such as bones, teeth or shells are preserved as such in the earth's atmosphere, which is not the common method of fozzilization.
2. When marine animals die, their hard parts such as bones, shells etc. are covered with sediments and are protected from further deterioration.
3. Such parts get preserved in vast ocean, the salinity in them prevents decay.
4. The sediments become hardened to form definite layers (or) strata.
5. For example wooly mammoth that lived 22 thousand years ago were preserved in the frozen coast of Siberia as such, several human beings and animals living in the animals living in the ancient city of pompeii were preserved infact by volcanic ash which gushed out from Mount Vesuvivs.
(ii) Petrifaction
1. After death of animals their original portion of their body may be replaced molecule for molecule by minerals and the original substance being lost through disintegration.
2. This method of fozzilation is called pertifaction.
3. The principle minerals involved in this type fozzilation are iron, pyrites, silica, calcium, carbonate, and bicarbonates of calcium and magnesium.
(iii) Natural moulds and casts
1. 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.
2. The cavities of the moulds may get filled up by hard minerals and get fozzillized, which are called casts.
3. Hardened faecal. matter termed as coprolites occur as tiny pellets.
4. Analysis of the coprolites enable us to understand the nature of diet, the pre historic animals thrived on.

1. Fitness according to Darwin refers ultimately and only to reproductive fitness
2. Those individuals who are better fit in an environment leave more progeny than the others the populations come to posses more fit individuals as nature selects for fitness.
3. The so called fitness is based on characteristics which are inherited hence there must be. genetic basis for getting selected and to evolve.