Evolution

Ncert 12 biology Q n A

the origin of life is considered a unique event in the history of the universe. true or false

true

how old is the universe

20 billion years old

what comprise the universe

huge clusters of galaxies

what are galaxies made of

gas and dust

what is the Big Bang Theory

1. attempts to explain the origin of universe

2. talks of a singular huge explosion unimaginable in physical terms

3. universe expaknded and then the temperature came down

4. H2 and He formed

5. the gases condensed under gravitation and formed the galaxies of the present day universe

when was Earth formed

4.5 billion years ago

what gases were present on Earth

1. water vapour

2. methane

3. carbon dioxide

4. ammonia released from molten mass

role of UV light in the formation of Earth's atmosphere

The UV rays from the sun brokeup water into Hydrogen and Oxygen and the lighter H2 escaped

how was water and CO2 formed on Earth

Oxygen combined with ammonia and methane to form water

how were the oceans formed on Earth

the water vapor fell as rain

when did life appear on Earth

4 bya

explain the theory of Panspermia

1. Some scientists believe that life came from outside.

2. Early Greek thinkers thought units of life called spores were transferred to different planets including earth.

3. 'Panspermia' is still a favourite idea for some astronomers.

explain the theory of spontaneous generation

For a long time it was also believed that life came out of decaying and rotting matter like straw

who proved that life comes only from pre-existing life

Louis Pasteur

explain the swan neck bottle experiment

LP showed that in pre-sterilised flasks

explain the chemical evolution theory by Oparin and Haldane

1. Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.)
   2. formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents.

conditions on earth

high temperature, volcanic storms, reducing atmosphere containing CH4 , NH3 , etc.

explain Miller's experiment to prove Oparin and Haldane's theory

1. In 1953 S.L. Miller, an American scientist created similar conditions in a laboratory scale.
   2. He created electric discharge in a closed flask containing CH4 , H2 , NH3 and water vapour at 800C.
   3. He observed formation of amino acids.
   4. In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.

when did the first non cellular life form arise

3 bya

non cellular life was made of

RNA Protein Polysaccharide

when did the first cellular life arise

2 bya

what was the type of cellular life

single celled and lived in water only

explain the theory of biogenesis

a biogenesis i.e., the first form of life arose slowly through evolutionary forces from non-living molecules is accepted by majority.

explain the theory of special creation

1. one, that all living organisms (species or types) that we see today were created as such.
   2. Two, that the diversity was always the same since creation and will be the same in future also.
   3. Three, that earth is about 4000 years old.

when was the theory of special creation strongly challenged

19th century

Charles Darwin's boat name

HMS Beagle

explain the theory of evolution of life forms

1. Based on observations made during a sea voyage in a sail ship called H.M.S. Beagle round the world Charles Darwin concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago.
   2. Many such life forms do not exist any more. There had been extinctions of different life forms in the years gone by just as new forms of life arose at different periods of history of earth.
   3. There has been gradual evolution of life forms. Any population has built in variation in characteristics.
   4. Those characteristics which enable some to survive better in natural conditions (climate, food, physical factors, etc.) would outbreed others that are less-endowed to survive under such natural conditions

what if fitness according to Darwin

fitness of the individual or population. The fitness

what is natural selection

those who are better fit in an environment

where did Alfred Wallace work

Malay Archipelago

The geological history of earth does not closely correlates with the biological history of earth. true or false

false

explain paleontological evidence

1. Palaeontology is study of fossils.

2. Fossils are remains of hard parts of life-forms found in rocks.

3. Rocks form sediments and a cross-section of earth's crust indicates the arrangement of sediments one over the other during the long history of earth.

4. Different-aged rock sediments contain fossils of different life-forms indicating the geological period in which. That life form existed.

5. Certain life forms are restricted to a certain geological time span.

how is the age of fossils calculated

radioactive dating

who provided embryological support for evolution and what was it

1. Ernst heckel

2. based upon the observation of certain features during embryonic stage common to all vertebrates that are absent in adult.

3. For example the embryos of all vertebrates including human develop a row of vestigial gill slit just behind the head but it is a functional organ only in fish and not found in any other adult vertebrates.

who disproved Ernst Heckel

the proposal was disapproved on careful study performed by Karl Ernst von Baer. He noted that embryos never pass through the adult stages of other animals

Comparative anatomy and morphology shows similarities and differences among organisms of today and those that existed years ago. true or false

true (Such similarities can be interpreted to understand whether common ancestors were shared or not)

which organisms share similarities based on the pattern of bones in forelimbs

whales

how is their anatomical structure similar

Though these forelimbs perform different functions in these animals

what is divergent evolution and homologous organs

the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous

homology indicates what

common ancestry

other examples of homology

vertebrate heart or brains

thorn and tendrils of Bougainvillea and Cucurbita represent

homology

explain analogy with the help of an example

1. Wings of butterfly and of birds look alike.

2. They are not anatomically similar structures though they perform similar functions.

3. Hence analogous structures are a result of convergent evolution - different structures evolving for the same function and hence having similarity.

other examples of analogy

1. eye of octopus and of mammals

2. flippers of penguins and dolphins

3. sweet potato (root) and potato (stem)

reason behind convergent evolution/analogy

One can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function

what are some biological similarities that point to the same shared ancestry as structural similarities among diverse organisms

similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.

explain how man has created breeds that differ from other breeds

1. Man has bred selected plants and animals for agriculture, horticulture, sport or security.
   2. Man has domesticated many wild animals and crops.
   3. This intensive breeding programme has created breeds that differ from other breeds (e.g., dogs) but still are of the same group.

give an observation supporting natural selection evolution

1. In a collection of moths made in 1850s, i.e., before industrialisation set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths.
   2. However, in the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed.

give reasons for industrial melanism

1. The explanation put forth for this observation was that 'predators will spot a moth against a contrasting background.

2. During post Industrialisation period the tree trunks became dark due to industrial smoke and soots.
   3. Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived.
   4. Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees - in that background the white winged moth survived but the dark-coloured moth were picked out by predators.

explain the significance of lichen in the above observation

1. lichens are used as industrial pollution indicators and will not grow in areas that are polluted

2. Hence moths that were able to camouflage themselves, i.e., hide in the background, survived.

what about in areas where industrialization didnt occur

in areas where industrialisation did not occur e.g. in rural areas, the count of melanic moths was low. This showed that in a mixed population, those that can better-adapt, survive and increase in population size. Remember that no variant is completely wiped out.

explain evolution by anthropogenic action with the help of examples

1. excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale.
   2. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries.

evolution is a directed process in the sense of determinism. true or false

false. it is not

It is a stochastic process based on chance events in nature and chance mutation in the organisms. this is in lieu of

evolution

define adaptive radiation

process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.

explain adaptive radiation in Australian marsupials

1. A number of marsupials each different from the other evolved from an ancestral stock, but all within the Australian island continent.
   2. When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats), one can call this convergent evolution.
   3. Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be 'similar' to a corresponding marsupial.

give the paired organisms showing convergent evolution of Australian marsupials and placental mammals

mole - marsupial mole anteater - numbat mouse - marsupial mouse lemur - spotted cuscus flying squirrel - flying phalanger bobcat - tasmanian tiger cat wolf - tasmanian wolf

adaptive ability is inherited. true or false

true (it has a genetic basis)

define fitness

Fitness is the end result of the ability to adapt and get selected by nature.

what are the 2 key concepts of Darwinian theory of Evolution

1. Branching descent

2. natural selection

Explain Lamarck's theory of evolution

1. Even before Darwin, a French naturalist Lamarck had said that evolution of life forms had occurred but driven by use and disuse of organs.
   2. He gave the examples of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks.
   3. As they passed on this acquired character of elongated neck to succeeding generations, Giraffes, slowly, over the years, came to acquire long necks.

Is evolution a process or the result of a process?

1. The world we see, inanimate and animate, is only the success stories of evolution.
   2. When we describe the story of this world we describe evolution as a process.
   3. On the other hand when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection.
   4. We are still not very clear whether to regard evolution and natural selection as processes or end result of unknown processes.

It is possible that the work of Thomas Malthus on populations influenced Darwin. explain

1. Natural selection is based on certain observations which are factual.

2. For example natural resources are limited, populations are stable in size except for seasonal fluctuation, members of a population vary in characteristics (infact no two individuals are alike) even though they look superficially similar, most of variations are inherited etc.
   3. The fact that theoretically population size will grow exponentially if everybody reproduced maximally (this fact can be seen in a growing bacterial population) and the fact that population sizes in reality are limited, means that there had been competition for resources.
   4. Only some survived and grew at the cost of others that could not flourish.
   5. The novelty and brilliant insight of Darwin was this: he asserted that variations, which are heritable and which make resource utilization better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny. 6. Hence for a period of time, over many generations, survivors will leave more progeny and there would be a change in population characteristic and hence new forms appear to arise.

what did Hugo de Vries propose

In the first decade of twentieth century, Hugo deVries based on his work on evening primrose brought forth the idea of mutations - large difference arising suddenly in a population.
He believed that it is mutation which causes evolution and not the minor variations (heritable) that Darwin talked about.

differntiate between Darwinian and de Vries's propositions

1. Mutations are random and directionless while Darwinian variations are small and directional.

2. Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation)

explain the Hardy-Weinberg Principle

1. This principle says that allele frequencies in a population are stable and is constant from generation to generation.

2. The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1.

difference in the measure of frequency shows

When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change.

disturbance in genetic equilibrium would be interpreted as

Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.

what are the 5 factors affecting Hardy-Weinberg equilibrium

1. gene migration or gene flow

2. genetic drift,

3. mutation,

4. genetic recombination

5. natural selection

explain gene migration

When migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population.

when does gene flow happen

There would be a gene flow if this gene migration happens multiple times.

what is genetic drift

If the same change occurs by chance

define founders effect

Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect.

what results in specialtion? how did we find this out

Microbial experiments show that pre-existing advantageous mutations when selected will result in observation of new phenotypes. Over few generations

explain natural selection and mutations

1. Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave greater number of progeny.

2. A critical analysis makes us believe that variation due to mutation or variation due to recombination during gametogenesis

differentiate between stabilization directional change and disruption.

Stabilization	Directional changes	Disruption
1. Individuals acquire mean character value.	1. More individuals acquirevalue other than the mean character value	1. More indivisuals acquire peripheral character value at both ends of curve
2. Peak is higher and narrower.	2. Peack shifts to one direction	2. Two peaks formed

when were invertebrates formed and active

500 mya

jawless fish

350 mya

sea weed and few plants

320 mya

first organisms that invaded land were

plants

Fish with stout and strong fins could move on land and go back to water. This was about

350 mya

when and where was a Coelacanth caught

In 1938 in South Africa

what is the evolutionary significance of Coelacanth

lobefins evolved into the. first amphibians that lived on both land and water

ancestors of modern day frogs and salamanders was

lobe fins

amphibians evolved into

reptiles

differnece between reptiles and amphibians

they lay thick shelles eggs which do not dry up in sun unlike those of amphibians

modern day descendants of reptiles

Turtles

function of Giant pteridophytes

Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly.

When did ichthyosaurs go back into water?

Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs).

land reptiles were

dinosaurs

biggest dinosaur

The biggest of them Tyrannosaurus Rex

when did the dinosaurs disappear

About 65 mya

the first mammals were like

shrews - small sized fossils

when reptiles came down who took over this earth

mammals (There were in South America mammals resembling horse

what happened to them after South American drift

Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.

why did the marsupials of Australia survive

Due to the same continental drift pouched mammals of Australia survived because of lack of competition from any other mammal

mammals that live wholly in water

whales dolphins, seals and sea cows are some examples.

about 15 mya which primates existed

Dryopithecus - ape like Ramapithecus - man like They were hairy and walked like gorillas and chimpanzees.

Few fossils of man-like bones have been discovered

Ethiopia and Tanzania

what did this lead to

These revealed hominid features leading to the belief that about 3-4 mya, man-like primates walked in eastern Africa. They were probably not taller than 4 feet but walked up right.