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Convergent evolution refers to the evolutionary process of selection of similar adaptive features in different groups of organisms in a similar habitat towards the same function.

• It is the similar habilat that has resulted in selection of similar structures.
• Analogous structures that are not anatomically similar but perform the same functions result from convergent evolution.

Examples: Wings of butterfly and wings of birds.

Pre-existing variations are the most important pre-condition for adaptive radiation.

Frequency of allele  B = all BB + 1/2 of Bb

= 36 + 1/2 x 48

= 36 + 24

= 60%

Frequency of allele b = all bb + 1/2 Bb

= 16 + 1/2 x 48

= 16 + 24

= 40%

Natural resources are limited, populations are stable in size, members of a population vary in characteristics even though they look superficially similar. Theoretically, population will increase exponentially but the population sizes in reality are limited thus leading to competition. Only the ones which are fit and adapt themselves are able to survive. They grow at the cost of others and flourish. This was called as natural selection by Darwin.

Experimental evidence of chemical evolution/Miller’s experiment 

▪ Experiment was performed by S.L. Miller and H.C. Urey in 1953. 

▪ Experimental set-up: In a closed flask containing CH₄, H₂, NH₃ and water vapour at 800°C, electric discharge was created. The conditions were similar to those in primitive atmosphere. 

▪ Observations: After a week, they observed presence of amino acids and complex molecules like sugars, nitrogen bases, pigments and fats in the flask. 

▪ Conclusions:. 

i. It provides experimental evidence for the theory of chemical origin. 

ii. It showed that the first non-cellular form of life was created about 3 billion years ago. 

iii. It showed that non-cellular biomolecules exist in the form of DNA, RNA, polysaccharides and protein.

DDT resistance in mosquitoes and Antibiotic resistance in microbes.

Anthropogenic action i.e. human activities has led to the evolution of a number of new species in a short time scale. This hastens the process of evolution. For example excess use of herbicides & pesticides, in crop production, has resulted in selection of resistant varieties of pests, in a much lesser time scale//use of antibiotics or drugs, against microbes, leads to resistant organism, in lesser time scale.

Charles Darwin travelled around the world by a sea voyage in a sail ship called H.M.S. Beagle.

He observed the gradual evolution of life forms in Galapagos Island and Malay Archipelago.

All the existing life forms share similarities and share common ancestors present at different periods in the history of earth (epochs, periods and eras). 

a. (ii) and (iii) are analogous structures. 

b. Convergent evolution.

a. (i) Forelimbs of whales and bats. (iv) Thorns of Bougainvillea and tendrils of Cucurbita. 

b. Divergent evolution.

Hugo de Vries put forth the Mutation theory. Mutations are sudden random changes that occur in an organism that is not heritable. De Vries carried out his experiments in the Evening Primrose plant (Oenothera lamarckiana) and observed variations in them due to mutation. 

According to de Vries, sudden and large variations were responsible for the origin of new species whereas Lamarck and Darwin believed in gradual accumulation of all variations as the causative factors in the origin of new species.

Gene mutation refers to the changes in the structure of the gene. It is also called gene / point mutation. It alters the phenotype of an organism and produces variations in their offsprings.

1. Pennsylvanian 

2. Mississippian

(a) A is true R is false

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.

(b) Small sized population

Wisdom teeth, Mammae in male, Body hair and Coccyx.

1. The theory of use and disuse – Organs that are used often will increase in size and those that are not used will degenerate. Neck in giraffe is an example of use and absence of limbs in snakes is an example for disuse theory. 

2. The theory of inheritance of acquired characters – Characters that are developed during ’ the life time of an organism are called acquired characters and these are then inherited.

The biogenetic law is not universal and it is now thought that animals do not recapitulate the adult stage of any ancestors. The human embryo recapitulates the embryonic history and not the adult history of the organisms.

Coprolites are the hardened faecal matters occurs as small pieces. Analysing the coprolites helps to understand the nature of diet of prehistoric animals.

1. Ontogeny refers to the life history of an individual. 

2. Phytogeny refers to the evolutionary history of a race.

Molecular evolution is the process of change in the sequence composition of molecules such as DNA, RNA and proteins across generations. It uses principles of evolutionary biology and population genetics to explain patterns in the changes of molecules.

One of the most useful advancement in the development of molecular biology is proteins and other molecules that control life processes are conserved among species. A slight change that occurs over time in these conserved molecules (DNA, RNA and protein) are often called molecular clocks. Molecules that have been used to study evolution are cytochrome (respiratory pathway) and rRNA (protein synthesis).

Actual remains – The original hard parts such as bones, teeth or shells are preserved as such in the Earth’s atmosphere. This is the most commpn 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 the ancient city of Pompeii were preserved intact by volcanic ash which gushed out from Mount Vesuvius.

Movement of genes through gametes or movement of individuals in (immigration) and out (emigration) of a population is referred to as gene flow. Organisms and gametes that enter the population may have new alleles or may bring in existing alleles but in different proportions than those already in the population. Gene flow can be a strong agent of evolution.

Cro-Magnon was one of the most talked forms of modem human found from the rocks of CroMagnon, France and is considered as the ancestor of modem Europeans. They were not only adapted to various environmental conditions, but were also known for their cave paintings, figures on floors and walls.

1. Mesozoic era is divided into three periods namely Triassic, Jurassic and Cretaceous. 

2. Dominating Fauna : Reptiles and Dinosaurs Dominating 

3. Flora : Conifers, Ferns and Ginkgon.

CO₂ , NH₃ , UV and Water vapour

Australopithecus lived in East African grasslands about 5 mya and was called the Australian ape man. He was about 1.5 meters tall with bipedal locomotion, omnivorous, semi erect, and lived in caves. Low forehead, brow ridges over the eyes, protruding face, lack of chin, low brain capacity of about 350 – 450 cc, human like dentition, lumbar curve in the vertebral column were his distinguishing features.

Divergent Evolution:

1. Divergent evolution is a result of homology. 

2. Eg: The wings of bird and the forelimbs of human both are homologous structures modified according to functions. In birds, it is used for flight and in humans used for writing and other purposes.

Convergent Evolution:

1. Convergent evolution is a result of analogy,

2. E.g: Root modification in sweet potato, and stem modification in potato are analogous structures both performing same function i.e., storage,

Correct Answer is: (b) 0.42

Natural selection, Genetic drift, Mutation and Geneflow

1. Homo habilis: The brain capacity was between 650-800 cc. They were probably vegetarians.

2. Homo erectus: The brain capacity was around 900 cc. They probably ate meat.

Homo sapiens or modem human arose in Africa some 25,000 years ago and moved to other continents and developed into distinct races. They had a brain capacity of 1300 – 1600 cc. “They started cultivating crops and domesticating animals.