Evolution Question Answers: NCERT Class 12 Biology

Fossils are the hard remains or impressions of the dead animals (ancient organisms) preserved layer by layer in the sedimentary rocks. They are formed during sedimentary rock formation, the dead animals of the sea, large lakes carried to the rivers and sinks down then get buried in rocks. The oxygen get low which prevents from decay and the animals which preserved in rocks. The deeper layer of the fossils described the earlier fossils and upper layer had more recent fossils. Fossil record shows great changes in the kind of organisms that dominated life on earth at different points in time.

Gene frequency or allele frequency is the proportion of the allele in the gene pool as compared with the another at the same locus and they are estimated form the genotypic frequencies.

There are five factors that are responsible for the failure of Hardy- Weinberg equilibrium: gene flow, genetic drift, non-random mating or genetic recombination, natural selection and mutation. This law states that with the random mating, the genes and the genotypic frequencies persist the same generation after generation. There are some assumption that are necessary for this law, population should be panmictic and there would be no natural selection, no mutation, no migration occurs.     

Genetic drift is the random change in the allelic frequency simply as the result of result of chances from one generation to the next in a finite population. Darwin defined the process of natural selection in which the kind of organisms in a population that are best adapted to the environment increases in frequency relative to less adapted forms over a number of generations. Mutation is the source of all genetic variations and is considered as random phenomenon. This randomness of mutation was first demonstrated by Luria and Delbruck in 1943. Gene flow is the transfer of genetic material from one population to another and if its rate is high then two population will have equivalent allele frequencies which is considered as single effective population. And, the exchange of genetic material between different organisms that leads to the production of offspring with the combination of traits is genetic recombination.        

There are two forms of genetic drift and founder effect is one of them. Founder effect occurs when the small group of individuals (called founder’s population) become isolated from the large population to form a colony. Population in the new settlement like; Larger the founder population the more likely it will resemble the parent population. The smaller number of the individuals as founders might not possess all the alleles and might display different frequency. Formation of different genotype in the new settlement is called the founders effect.

Note*: The founding individuals may not represent the entire genetic diversity of the original population, i.e. the alleles in the founder population will be present at the different frequencies and some may be missing altogether.

Ramapithecus was more man- like while Dryopithecus was ape- like. Dryopithecus is considered to be the ancestors of both apes (chimpanzee, gorilla) and humans. They are closely related to the chimpanzee but had arms and legs of approximately equal length, heels it its feet indicates the semi-erect posture. The human DNA is approximate 98.4 % similar to that of chimpanzees. On the basis of genomic studies, we have found that humans and chimpanzee ancestors diverged and then converged. Ramapithecus lived on the open grassland, have thickened tooth enamel, shorter canines, robust jaws and hence, showed a hominid status.  

The first hominid was known ‘Homo habilis’. It was the first human, or the first recognizable human species which is designated as the Handyman or also known as the ‘tool maker’ which has been called because rudimentary tools have been found with the fossils of this species. They had a brain larger than Australopithecus and also had some similarities with the Australopithecus africanus.     

Among all three of them, Ramapithecus was the one who never ate meat. Ramapithecus lived on the open grassland, have thickened tooth enamel, shorter canines, robust jaws and hence, showed a hominid status. They couldn’t ate meat cause of their dental structure and ate hard nuts and seeds like modern man.  Molars show the wear and tear method that indicates Ramapithecus were the “tough Herbivores” and their diet includes variety of nuts, seeds and grasses. 

Yes, aquatic life forms get fossilised due to the geological upheavals as this raised many of the stratified rocks above the surface of the sea and bring their preserved life or fossils. The dead animals of the sea or large lakes and of the land carried to the sea or large lakes carried to the rivers and sinks down then get buried in rocks. The oxygen get low which prevents from decay and the animals which preserved in rocks. Thus the hard parts remains of the dead animals and that forms fossils.

‘Simple organisms’ and ‘Complex organisms’ terms defines the evolutionary history of the organism. Simple organism is considered to be primitive having simple structural and functional organization. On the other hand, complex organisms considered to be more evolved which are having complex structural and functional organization; and they are believed to have arisen from the simpler forms that leads to evolution.

Simple organisms are unicellular (single celled organisms) and contains basic characteristics; cannot be seen with the naked eyes (for example: bacteria, amoeba, and paramecium). Complex organisms are multicellular, contains organs system; single species form a community or population; and contains advance features (for example: mammals).

Age of the living tree can be identified by measuring the circumference of the tree, four to five feet up on the trunk and divide the circumference by the pi (3. 14) and the diameter will be the answer. And then compare the value with the chart from the Morton arboretum to find the approximate age. We can also determine the age of the tree by counting the number of rings by cutting the tree that are present in the trunk of the living tree. When the tree is cut, light and dark colour layers appeared. Note the cross section of the tree ring and then count the dark rings, you will found tree’s age.

When the unrelated animals converging on the same structure or same form because they are adaptive in the same environment, this type of evolution is known as convergent evolution and this produces analogous structures. For example: streamlined shape of sharks and dolphins (their body shape, fins and flippers are same but they belongs to different lineages; shark is an elasmobranch fish belongs to Pisces and dolphin is an aquatic mammal). And they are adapted for swimming. Another example is: wings in bats, birds and flies and they are adapted for flying. 

There are various methods for the determination of age of fossils and these are following:

1. Relative dating method: relative dating of the rocks was carried out by estimating the position and the rate of erosion in particular environment. Older rocks, being deeper had older or ancient fossils; and superficial rocks had more recent fossils. It does not tell any specific dates, only estimates whether the object is younger or older that are found at the site.
2. Absolute dating method: this method determines how much time have passed since the rock formation occurred by measuring the radioactive decay; or based on the property of spontaneous decay of unstable radioactive nuclei into stable form at the constant rate. This involves three techniques: Uranium- Lead Technique, Carbon (C¹⁴) Dating Technique and Potassium- Argon Technique. 

Evolution from the single or common ancestral species is the most important pre- condition for adaptive radiation. During the Eocene and Oligocene period, most of the orders of mammals are originated by going into the ecological niches that were vacated by the extinct dinosaurs. This type of evolution from the common ancestral species to variety of forms which occupy different habitat is known as adaptive radiation. And, this concept was developed by H.F. Osborn in 1898. Example: Darwin’s finches of the Galapagos Island, varies into limb structure of mammals.    

Age of the rocks and fossils are determined by the same methods like relative dating method and absolute dating method which also involves some techniques:

1. Uranium- Lead Technique: it is the geological age determination method which uses the radioactive decay of uranium into the stable form of lead. Over the time half of total uranium disintegrates into lead. By the ratio of uranium to lead in the rock or a fossil, age can be found out.
2. Carbon (C¹⁴) Dating Technique: radiocarbon dating method is used for determining the age of the rock by using the properties of radioactive isotope of the carbon. Carbon (C¹⁴) decays to form nitrogen¹⁴.

Macromolecules are made from the single subunits or building blocks which are known as monomers and they are combined to form large molecules known as polymers. Functional macromolecules like lipids, proteins, enzymes, antibodies etc. are evolving the variants and the better adapted complex organisms. Example: enzymes of Kreb’s cycle in which, evolution occurred towards their new structure and functions.   

Darwinian selection theory states that individuals with favourable variations are better adapted than individuals with less favourable variation. It means that nature selects the individuals with useful variation as these individuals are better evolved to survive in the existing environment. An example of such selection is antibiotic resistance in bacteria. When bacterial population was grown on an agar plate containing antibiotic penicillin, the colonies that were sensitive to penicillin died, whereas one or few bacterial colonies that were resistant to penicillin survived. This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug. Hence, the resistant bacteria multiplied quickly as compared to non-resistant (sensitive) bacteria, thereby increasing their number. Hence, the advantage of an individual over other helps in the struggle for existence.

The evolution of horse started with Eohippus during Eocene period. It involved the following evolutionary stages.

(i) Gradual increase in body size

(ii) Elongation of head and neck region

(iii) Increase in the length of limbs and feet

(iv) Gradual reduction of lateral digits

(v) Enlargement of third functional toe

(vi) Strengthening of the back

(vii) Development of brain and sensory organs

(viii) Increase in the complexity of teeth for feeding on grass

The evolution of horse is represented as

(i) Eohippus

It had a short head and neck. It had four functional toes and a splint of 1 and 5 on each hind limb and a splint of 1 and 3 in each forelimb. The molars were short crowned that were adapted for grinding the plant diet.

(ii) Mesohippus

It was slightly taller than Eohippus. It had three toes in each foot.

(iii) Merychippus

It had the size of approximately 100 cm. Although it still had three toes in each foot, but it could run on one toe. The side toe did not touch the ground. The molars were adapted for chewing the grass.

(iv) Pliohippus

It resembled the modern horse and was around 108 cm tall. It had a single functional toe with splint of 2nd and 4th in each limb.

(v) Equus

Pliohippus gave rise to Equus or the modern horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.

Fossils of dinosaurs have revealed the evolution of reptiles in Jurassic period. As a result of this, evolution of other animals such as birds and mammals has also been discovered. However, two unusual fossils recently unearthed in China have ignited a controversy over the evolution of birds.Confuciusornis is one such genus of primitive birds that were crow sized and lived during the Creataceous period in China.

Species can be defined as a group of organisms, which have the capability to interbreed in order to produce fertile offspring and do not breed with members of other species.

The various components of human evolution are as follows.

(i) Brain capacity

(ii) Posture

   iii.            Food / dietary preference and other important features

There are many animals other than humans, which have self consciousness. An example of an animal being self conscious is dolphins. They are highly intelligent. They have a sense of self and they also recognize others among themselves and others. They communicate with each other by whistles, tail-slapping, and other body movements. Not only dolphins, there are certain other animals such as crow, parrot, chimpanzee, gorilla, orangutan, etc., which exhibit self-consciousness.

The modern day animals and their ancient fossils are listed in the following table.

You can draw image of any animals of your wish.

Adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage. This process occurs due to natural selection. An example of adaptive radiation is Darwin finches, found in Galapagos Island. A large variety of finches is present in Galapagos Island that arose from a single species, which reached this land accidentally. As a result, many new species have evolved, diverged, and adapted to occupy new habitats. These finches have developed different eating habits and different types of beaks to suit their feeding habits. The insectivorous, blood sucking, and other species of finches with varied dietary habits have evolved from a single seed eating finch ancestor.

No, human evolution cannot be called adaptive radiation. This is because adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage, which is not the case with human evolution. Human evolution is a gradual process that took place slowly in time. It represents an example of anagenesis.