ECOLOGY:Branch of Science which deals with relationship between organisms & their physical & biological environment.

LEVELS OF ORGANISATION:
•          Organisms- every individual of a species
•          Population- individuals of the same species at a given place
•          Communities- assembly of population of all different species living in an area and interacting.
•          Biomes- large unit of flora and fauna in a specific climatic zone

ENVIRONMENT
Sum of all biotic and abiotic factors that surround and influence an organism in it’s survival and reproduction.

Factors affecting environment:
•          Rotation of earth
•          Seasonal and annual  variation in temperature and precipitation
•          Habitats

MAJOR BIOMES
1.       Artic & Alpine Tundra
2.       Coniferous Forest
3.       Temperate Forests
4.       Grassland
5.       Tropical Forest
6.       Desert

MAJOR  ABIOTIC FACTORS
•          Temperature
•           Water
•           Light
•           Soil
Temperature
•          Ecologically most imp. Factor
•          Decreases progressively from equator towards pole and from plane to mountain tops
•           Polar Region and high altitudes- sub zero level Tropical deserts > 50°C
•          Organisms survive only in suitable range of temperature
•          Based on tolerance to temperature

            -   Eurythermal
                Organisms that tolerate wide range of temperature
            -   Stenothermal
                Organisms that tolerate only narrow range of temperature

Water
•          Life on earth originated in water
•           Productivity and distribution of plants depends on water

Based on tolerance to salinity
             - Euryhaline
                Organisms that can tolerate wide range of salinity
             - Stenohaline
                Organisms that can only tolerate narrow range of salinity

•          Freshwater animals cannot live in sea water and vice versa because of osmotic problems.

Light
•          sunlight source of energy- photosynthesis
•           Small plants (canopied by tall plants) adapted to photosynthesize at low light conditions.
•           Flowering dependent on sunlight
•           Foraging, Reproductive and migratory activities of animals depend on seasonal variation in light intensity
•           UV component – harmful to organisms

Soil
Nature of soil depends on
I.            climate
II.           weathering process
III.          sedimentary or transported
IV.          soil development

Characteristics of soil
a.       soil composition
b.      grain size
c.       aggregation- determine percolation and water holding capacity of soil

RESPONSES TO ABIOTIC FACTORS
Homeostasis: The ability of an organism to maintain the constancy of its internal environment despite varying external environmental conditions.

Q: How does Homeostasis occur?

1. Regulate: maintain homeostasis by ensuring constant body temp (thermoregulation), and constant osmotic concentration (osmoregulation). Examples – mammals regulate temperature by  shivering in cold and sweating in heat
 Picture
2. Conform: internal environment of conformers changes with external environment

Q:Why small animals are rarely found in polar regions?

A: Small animals have large surface area compared to volume so they lose heat easily in cold and have to expend energy to generate body heat.

But, if stressful external conditions are localized or remain for short duration, then alternatives are migrate / suspend.

3. Migrate: Move from stressful habitat temporarily to hospitable area and return when stressful period over.

E.g.- Migration of birds to Keolado National Park, Rajasthan from Siberia

4. Suspend: Organisms develop mechanisms to deal with stressful situation

Examples- Spores (bacteria and fungi)

                - Seeds (angiosperms)- dormancy
                - Hibernation (Bears)
                - Aestivation ( snails)
                - Diapause (stage of suspended development) in zoo plankton

Adaptation

Any ability of an organism that enables an organism to survive and reproduce in its habitat

ADAPTATIONS IN ORGANISMS

1. Kangaroo rat: internal fat oxidation to produce water as by product- concentrated urine
2.Desert plants: thick cuticle, stomata in deep pits to minimize transpiration and special photosynthetic pathway (CAM).  Ex. OPUNTIA - leaves reduced to spines, photosynthetic stems
3. Cold climate mammals: short ears and limbs to minimize heat loss. This is Allen’s Rule.
4. People living at high altitude: increased RBC production and increased breathing rate
5. Desert lizards: bask in sun when cold and move to shade when hot.

POPULATION

Group of individuals living in a well defined area which share or compete for similar resources and potentially interbreed

Example: Lotus plants in a pond

                Bacteria in a culture plate

Population ecology is therefore, an imp. area of ecology because it links ecology to population genetics and evolution

POPULATION ATTRIBUTES

1.Birth rate- Average no. of young ones born in  a period of time with reference to the  members of the population.
2. Death rates- Average no. of deaths in a period of time with reference to the members of the population.
3.Sex Ratio- No. of females and males per 1000 individuals
4. Age pyramid: Plot of age distribution (% individuals of a given age or age group)

It reflects whether growth is
   (i)            Expanding
   (ii)           Stable
   (iii)          Declining

 Picture
POPULATION DENSITY:
Number of individuals present per unit area at a given time.

POPULATION GROWTH
Factors affecting change in population density
Food availability
Predation pressure
Weather

Density changes by change in four basic processes
(a)    Natality              -     Increase population    
(b) Immigration      -    Increase population
(c)  Mortality           -    Decrease population
(d) Emigration        -    Decrease population

1.Natality (B) : Number of births during given period in the population that are added to the initial density
2.Mortality (D) : Number of deaths in the population during a given period.
3.Emigration (E) : Number of individuals of the population who left the habitat and went elsewhere during the given period
4. Immigration (I) : Number of individuals of the same species that have come into the habitat from elsewhere during the time under consideration.

If N is the population density at time ‘t’, then its density at time ‘t+1’
                             Nt+1 = Nt + [(B + I) – (D + E)]
Population density will increase if (B+I) > (D+E)

GROWTH MODELS
EXPONENTIAL
LOGISTIC

EXPONENTIAL GROWTH

•           When resources are unlimited, each species realizes its innate potential to grow in no. – population grows exponentially
•           N – Population size
                  b – Birth rates( per capita births)
                 d – Death rates (per capita deaths
                dN/dt – increase/decrease in N during time t

Then,   dN/dt = (b – d)*N
Let (b – d) = r, then
          dN/dt = r*N
Where, r – intrinsic rate of natural increase
For human population in 1981, r = 0.0205

Integral form of exponential growth eq.

                  Nt = N0ert

Where Nt = Population density after t
            N0 =Initial population density
            r   = Intrinsic rate of natural increase
            e  = base of natural logarithms

•           Species growing exponentially under unlimited resources reaches enormous population density in short time.

LOGISTIC GROWTH
•           No population has unlimited resources-leads to competition for resources
•          Fittest individual survive and reproduce
•          Carrying capacity (K)- Maximum population density a habitat’s resources can support
•          When a population has limited resources it shows
lag phase
phase of acceleration
asympote- population density = K  
 Picture
Verhulst Pearl Logistic Growth

                          dN/dt = rN [(K – N)/K]

Where   N = Population density at time t
             r = Intrinsic rate of natural increase
             K = Carrying capacity

•           As resources for most organisms are finite logistic growth more realistic

LIFE HISTORY VARIATIONS

•          Darwinian fitness – Reproductive fitness
•          Organisms adopt most efficient reproductive strategy suited to their habitat

Examples:

1. Breed once in lifetime – pacific salmon fish ,Bamboo
2. Breed many times in life time – birds,  mammals
3. Produce large no. of small sized offspring  - Oysters, pelagic fishes
4. Produce small no. of large sized offspring - birds, mammals

Ecologists say life history traits depend on constraints of biotic and abiotic parts


Population Interactions

Minimum requirement of species- one more species to feed on.

Interspecific interactions - Interactions of populations of two different species.

Types of Interactions:

Name of Interaction        Species A       Species B

Mutualism                         +                   +
Competition                       -                    -
Predation                          +                   -
Parasitism                         +                   -
Commensalism                   +                   0
Ammensalism                     -                    0

+   Positive effect                    -  Detrimental effect                      0  Neutral effect


PREDATION

It is an Interspecific Interaction where one animal kills and consumes the other weaker animal.

Roles of Predators
Transfer energy from plants to higher trophic levels (position of organism in food chain)
Control Prey population – Prickly pear cactus- moth
Biological control of Agricultural pest
Maintain species diversity by reducing intensity of competition among competing prey species

Q: Why predators are prudent?

A: Over exploitation of prey by the predators results in extinction of prey and predator.

Defense to lessen impact of predation
Insects and frog – camouflage
Monarch butterfly – poisonous

PLANTS MORPHOLOGICAL AND CHEMICAL DEFENCES
Thorns- cactus and Acacia
Produce and store chemical – Calotropis
Nicotine, Caffeine, Quinin, Strychnine, opium – against grazers & browsers

COMPETITION
Interaction either among individuals of same species or between individuals of different species.

Occurs among closely related species but not always true

1. Unrelated species also compete- flamingo & fish compete for zooplankton  
2. Feeding efficiency of a species reduce due to other species even if resources are plenty – Abingdon tortoise.


Evidence for competition
Competitive release – species distribution restricted to small areas due to competitively superior species.

GAUSE’S COMPETITION EXCLUSION PRINCIPLE
“Two closely related species competing for same resources cannot coexist as the competitively inferior one will be eliminated.”

Resource partition- Two competing species avoid competition by diff. feeding and foraging patterns-Mc Arthur (warblers foraging activities)

PARASITISM
It is the interaction where one species (parasite) depends on the other species (host) for food and shelter, host is harmed.

Parasites and host self-evolve.
Adaptations of parasites
               - Loss of unnecessary sense organs
               - Hooks and sucker
               - Loss of digestive system
               - High Reproductive capacity
Parasites-
     (i) Reduce the survival of host
     (ii) Growth and reproductive rate are reduced
     (iii) Render the host vulnerable to its predators by making them weak

Health:-
It can be defined as a state of complete physical, mental and social well-being.  When people are healthy, they are more efficient at work.

Health is affected by –
Genetic disorders – inheritable defects of parents to offspring.
Infections and
Life style including food and water we take, rest and exercise we give to our bodies, habits that we have or lack etc.

Diseases can be broadly grouped into infectious and non-infectious.  Diseases which are easily transmitted from one person to another, are called infectious diseases.  Among non-infectious diseases, cancer is the major cause of death.

Common Diseases in Humans:
Pathogen :- Disease causing organisms.

Typhoid:
Pathogen: Salmonella typhi.
Symptoms: High fever, weakness, stomach pain, constipation, headache and loss of appetite, intestinal perforation and death may occur in severe cases.  Typhoid fever could be confirmed by Widal test.
Mode of transmission: These pathogens generally enter the small intestine through contaminated food and water and migrate to other organs through blood.


Pneumonia:
Pathogen: Streptococcus pneumoniae and Haemophilus infuenzae.
Symptoms: the alveoli get filled with fluid leading to severe problems in respiration. Symptoms include fever, chills, cough and headache, in severe cases the lips and finger nails may turn gray to bluish in colour.
Mode of transmission: transmitted through droplets of infected persons.

Common Cold:
Pathogen: Rhino viruses.
Symptoms: nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness.
Mode of transmission: through droplets of infected persons.



DISEASES CAUSED BY PROTOZOANS.
Malaria.(means bad air)
Pathogen. Protozoan Plasmodium.
Vector.  Female Anopheles mosquito
Symptoms. Head aches, muscle pain, high fever.  During fever the patient feels chill and shivering.
Prevention.  Eradication of vector and keeping the surrounding clean.
Treatment. It involves the use of medicine like quinine and protection of patients from the mosquitoes.
Mode of spread. This disease spreads by the bite of infected Anopheles mosquito.  Only the female Anopheles is capable of spreading the disease because it sucks the blood of man.

Amoebiasis.
Pathogen.  It is due to an intestinal protozoan parasite Entamoeba histolytica.
Symptoms. This parasite lives in the large intestine and destroys the mucus membrane.  This may cause bleeding and ulcer that produce dysentery.  Hence patient passes out blood and mucus with the stool.  There will be severe pain in abdomen, fever, nausea and nervessness.
Mode of transmission:  As the cysts of pathogen are found in the intestinal discharge the possibility of infection to healthy persons is through contaminated water or improperly washed or cooked vegetables and fruits.  The pathogen can also be transmitted through dirty hands.
Prevention.  Proper disposal of faecal matter of the patient.  Vegetables and fruits when used raw, should be thoroughly washed.  Water should be boiled before drinking.


DISEASE CAUSED BY HELMINTHES WORM.

Ascariasis.
Pathogen.  A round worm Ascaris lumbricoides.
Symptoms.  This parasite is found in the small intestine of man and is of world wide distribution.  It  causes a lot of stomach ache, nausea and cough.
Mode of transmission:  Through food, when soil consist of cyst and eggs, it will be transmitted through vegetables growing on it or through dirty hands or by ingestion of soil.
Prevention: The disposal of human faeces by underground sewer canals is an efficient measure to prevent the spread.  Washing of vegetables and fruits before eating help of keep away the eggs of the worm.

Filariasis.
Pathogen.  Wuchereria bancrofti.
Vector.  Culex mosquito.
Symptoms. The worm lives in the lymph vessels and  block them, this causes swelling of the body parts like, legs scrotum, foot, etc.  This enlargement of legs gives the disease its name as Elephantiasis.
Prevention.  Eradication of vector.


DISEASE CAUSED BY FUNGI

Ringworms:
Pathogens: Trichophyton and Epidermophyton
Symptoms: appearance of dry, scaly lesions on various parts of the body such as skin, nails and scalp with intense itching.


Measures for prevention and control of infectious diseases –
Personal hygiene: It includes cleanliness of body, drinking of clean water, etc.
Public hygiene: It includes cleaning of water reservoirs, proper disposal of sewage, etc.

Immunity
Ability of the body to fight infectious agents
On the basis of the immunity possessed by the body, immunity can be innate immunity and acquired immunity.

1.  Innate immunityis a non-specific type of defense mechanism.
It has four types of barriers –
Physical barrier: Example, skin covering of the body, secretion of mucous in the respiratory tract
Physiological barrier: Example, acid in the stomach, tears from the eyes
Cellular barrier: Example, monocytes and lymphocytes in blood
Cytokine barrier: Example, interferon

2. Acquired immunity: itis a specific type of defense mechanism. It shows two types of responses: primary response and secondary response. It involves two types of lymphocytes –
B lymphocytes: Show humoral immune response (HI)
T lymphocytes: Show cell mediated immunity (CMI)

Structure of an Antibody:
The antibodies are protein molecules called immunoglobulins and are of various types like IgA, IgM, IgE, IgG.
Each antibody molecule consists of four polypeptide chains, two are long called heavy chains and other two are short called light chains. Both are arranged in the shape of ‘Y’, hence an antibody is represented as H2L2.

On the basis of production of antibodies, immunity can be further categorised as –
Active immunity: Body produces its own antibodies against antigens
Passive immunity: Readymade antibody is transferred from one individual to another
Colostrum (contains antibodies IgA) is an example of passive immunity provided by the mother to her child.

Auto immunity:
Production of antibodies against the tissues of its own cells. Example – Rheumatoid arthritis.

Lymphoid organs:
It acts as the sites of formation and maturation of lymphocytes.
Primary lymphoid organ – where lymphocytes are produced and matured. Example – Bone marrow and Thymus.

Secondary lymphoid organ– where lymphocytes fight with antigens. Example - Spleen, lymph nodes, tonsils, Peyer's patches Mucosal Associated Lymphocyte Tissues (MALT).


Vaccination:
It is the protection of the body from communicable diseases by administration of agents (called vaccines) that mimic the microbes. Vaccines are available against tetanus, polio, etc.


Allergies:
 Hypersensitivity to a particular allergen (such as pollens, dust) is termed as allergy. IgE is an antibody responsible for allergy.  Symptoms include, sneezing, watery eyes, running nose and difficulty in breathing. Allergy is due to secretion of histamine and serotonine by mast cells. Allergy is treated with anti-histamine, adrenaline and steroids.

  AIDS (Acquired immunodeficiency syndrome) :

It can spread –
through sexual contact with the infected person
from the mother to her child, through the placenta
infected blood transfusion
by the use of infected syringe
It is caused by HIV virus (a retro virus) and has RNA as genetic material. HIV stands for Human Immunodeficiency Virus.

When HIV virus enters the host cell, the virus enters into macrophages, where RNA replicates and forms viral DNA by the help of enzyme reverse transcriptase. The viral DNA gets incorporated into the host cell’s DNA and directs the infected cells to produce daughter viruses.  The macrophages continue to produce virus that enters the helper T-lymphocytes.  Thus the number of helper T-lymphocytes progressively decreases in the body and weaken the immune system.

Diagnostic test for AIDS: ELISA (enzyme-linked-immuno-sorbent assay)

Cancer
Tumour caused by abnormal and uncontrolled cell division. It is of two types –
Benign tumour: Remains confined to a particular location and does not spread
Malignant tumour: Cells divides and invades new locations by getting transported through blood to distant sites
Metastasis: Property of malignant tumour to invade the distant body parts, thereby initiating formation of new tumours.
Carcinogen: Cancer-causing agents; e.g., X-rays, UV rays
Cancer detection and diagnosis: Techniques involved are radiography, computed tomography and magnetic resonance imaging

Treatment of cancer:
Surgical – cancerous tissues are surgically removed.
Radiotherapy – tumor cells are irradiated lethally by radiation.
Chemotherapy – drugs are used to kill cancerous cells, but shows side effects like hair loss, anemia, etc.
Immunotherapy – patients are given with alpha-interferon which activate their immune system and help in destroying the tumor.


Drugs and Alcohol

Drugs and alcohol abuse includes –
Opioids:  Morphine is obtained from Poppy plant. It is a sedative (depressant) and pain killer. Heroin is chemically diacetylmorphine.  It slows down body functions. Example, Heroin (extracted from Papaver somniferum)
Cannabinoids: Itis obtained from Cannabis sativa. These are taken by inhalation and oral ingestion, they affect the cardiovascular system of the body. Example, marijuana, hashish, charas, ganja (obtained from Cannabis sativa),
Coca alkaloids / Cocaine: it is obtained from Erythroxylon coca.  It is taken by smoking.  It is a stimulant and activates central nervous system.
Hallucinogens: It is obtained from Atropa belladonna and Datura sp. LSD (Lysergic acid Diethylamide) is obtained from fungus.
Tobacco: it contains nicotine, which is stimulant. It stimulates adrenaline and increases the secretion of adrenaline. Smoking of tobacco leads to lung cancer, bronchitis, emphysema, coronary heart diseases.

Adolescence and Drug abuse
Adolescence is the period during which the child becomes matured.
It is between 12 – 18 years of age.
  Causes of drug abuse –
Curiosity
Adventure
Excitement
Experimentation
Stress or pressure to excel in examination

Effects of drug/alcohol abuse –
Reckless behaviour
Malicious mischief
Violence
Drop in academic performance
Depression, isolation, aggressiveness, etc.

Prevention and control –
Avoid peer pressure
Counselling and education
Take help from teachers, parents and peers
Take professional and medical help

CHAPTER – 7 : EVOLUTION

Theory of Special Creation:
                According to this theory, life originated on this earth from super natural powers like god.  He created all plants and animals, which appeared on earth in the form they exist today.  

Theory of Spontaneous generation or Abiogenesis:
                According to this theory life originated on earth from non-living objects spontaneously by a process called Abiogenesis (origin of life from non-living matter).  It was believed that fishes and frogs originated from mud, maggots arouse from decaying meat and insects from plant juices and microorganisms from air & water.  But later Louis Pasteur disproved this theory and stated that life originate from pre-existing life.

Conditions of Primitive earth/ Origin of life:
It is believed that earth has originated about 4,600 million years ago.  It is formed by the condensation and cooling from a cloud of gases and dust.  At first the earth was very hot and had various gases and vapour of several elements.  With the passage of time, the earth gradually cooled down and gases condensed.  Thus a solid crust of earth was formed.  There were torrential rains for thousands of years resulting in the formation of large water bodies like oceans. 

The earth’s atmosphere at the time was a reducing atmosphere and not an oxidizing one as today.  There were large quantities of hydrogen, nitrogen, water vapour, carbon monoxide, methane and ammonia in the primitive atmosphere.  However, free oxygen was not present, so the atmosphere is known as reducing atmosphere and this led to the continuous series of chemical reactions among the gases to form amino acids. Hence life originates from reducing atmosphere.  

The present atmosphere is oxidizing one and no life is originating today because oxygen will not allow any continuous series of chemical reaction and if any product is formed among the gases that will be oxidized.  

A.I. Oparin and J.B.S. Haldane believed that methane, ammonia and water vapours contain the kinds of atoms needed to form various substances such as alcohol and amino acids.  Accumulation of such organic compounds within the oceans, lakes, ponds, pools, etc. over million of years must have produced a kind of ‘hot soup’.  In this ‘hot soup’ or ‘Darwin’s warm little pond’ smaller organic compounds must have combined together to form larger organic compounds and various macromolecules like polypeptides, proteins, nucleic acids, carbohydrates etc.  These compounds then interacted to produce the first living cell.  So according to them, the first living cell arose from simple inorganic and organic non-living elements – a process called Abiogenesis. 

The energy for such chemical reactions must have come from the heat of the atmosphere and from the electrical energy of lightening.

The most important compound that initially formed is a nucleoprotein (nucleic acid and protein) since it is the chemical characteristic of genes.  They might have aggregated in various combinations and must have formed the colloidal masses at the base of oceans.  They formed the small globules. They are then covered by fatty acids to form their surface membranes.  This membrane also became selectively permeable so a specific organization inside was maintained. Experimental evidences have also shown that such types of cells formed are called as coacervates (pre-cell) and then they gradually transformed into a living cell. 

Then enzymes and other important compounds inside were formed. In the present day cells, all these macromolecules are formed by the actions of enzymes.  But the enzymes are protein in nature.  So initially all macromolecules were formed by non-enzymatic actions.

Urey and Miller experiment:
Stanley Miller and Harold C. Urey in 1953 tested the Oparin-Haldane theory.  They made an apparatus to circulate methane, ammonia, water vapour and hydrogen gases.  All these gases were put in a flask fitted with electrodes.  In another flask, water was being boiled continuously.  The electrical charges, to provide energy similar to lightening etc.  were passed for one week or more.  After that they collected and analysed the contents of the apparatus.  He was able to get a number of amino acids, some of which are known to be present in the proteins e.g., glycine, alanine, aspartic acid and glutamic acid.  Miller also got several of the simple acids that are known to occur in the living organisms such formic acid, acetic acid, propionic acid, lactic acid and succinic acid. 

Hence they proved the Oparin and Haldane theory and now it is clear that reducing atmosphere was essential for such abiotic synthesis.

Organic evolution:
It is defined as the process of gradual and orderly changes in organisms from one form to another over a period of millions of years.  It is a slow and continuous process.  

Morphological Evidences: 
Homologous organs (Divergent Evolution):
Organs having similar embryonic origin and basic plan, but differing in their functions are known as homologous organs.  E.g., The arm of man, the leg of a horse, the wing of a bat, the wing of a bird and the flippers of a seal have the same basic plan of development but they are used for different works. All of them possess humerus in upper arm, radius and ulna in the forearm, carpals in the wrist, metacarpals  in the palm and phalanges in digits.  They also show similarities in the arrangement of the muscles and nerves and also show same pattern of embryonic development.
Homology in plants:
In plants, the homologous organs are a thorn of Bougainvillea and a tendril in Cucurbita both arising in the axillary position, but perform different functions.  Thorn for protection and tendril for support.
Analogous organs (Convergent Evolution):
Organs having similar functions but different in their basic plan of development are known as analogous organs.  For example, the wing of insects and that of birds or bats are analogous structure.  Their basic plan of development is different but has a similar function of flying.  In insects wing is an extension of the integument whereas a birds wing is formed of bones covered with flesh, skin and feathers.  
In plants:
In Opuntia/Cactus, a stem is modified to look like a leaf and may perform the function of a leaf (photosynthesis).
In potato and sweet potato, potato is a stem tuber and sweet potato is a root tuber.  Storage of food is the same function.

Geological time scale:
It shows the ages of the various eras and periods together with the major groups of plants and animals that are believed to have existed during that period.  It helps in the study of palaeontology.  

It has been divided into 6 eras which are further divided into periods or epochs.  Each being characterised by some specific living forms and climatic changes geological time scale is the calender of earth past history indicating the evolution of life through time recorded in sequence of rocks. 

Biological Evolution:
The essence of Darwinian theory about evolution is natural selection.  Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.  

Lamarck’s concept of evolution/Inheritance of acquired characters:

This theory states that characters are acquired by animals in two ways,
The effects of environment
Use and disuse of body parts.

For example, the long neck of giraffe is explained by Lamarck on the same principle.  Giraffe, which lived in the dry and arid deserts of Africa, tried to reach the foliage high up on the trees to eat them as there was no vegetation on the ground.  In the process its neck and forelegs got stretched a bit and this was inherited to the next generation.  Then in the next generation same efforts were continued.  Gradually through many successive generations, we got giraffe having such a long neck and forelegs. 

                Lamarck’s idea of the use and disuse of body parts and the inheritance of acquired characters was not accepted by the scientists.  It was disproved by August Wiesmann.  He showed that even after cutting the tail of rats for several generations, no rat was born without a tail.  

Darwin’s Theory:
Charles Darwin and Alfred Russel Wallace independently gave the theory of evolution.  This theory is known as ‘Darwin’s theory of natural selection’ and is published in a book, “Origin of Species by Natural Selection”.  The main features of this theory are as follows, 

Reproduction:  All organisms reproduce and multiply enormously.  Eg.  A pair of mice produces dozens of young ones, insects lay thousands of eggs and plants also produce thousands of seeds.  
Variations:  No two individuals are alike.  They differ from each other in size, shape, behaviour, etc. even the offspring of the same parent are never exactly alike except identical twins. 
Struggle for existence:  All the offspring are not able to reach adulthood.  When offspring 

become adulthood, then they start to reproduce.  This reproductive capacity varies from animal to animal; some reproduce more and some minimum.  This differential capacity of reproduction is known as differential reproduction.

                Since the number of individuals is far more than actually can survive, so they compete among themselves for food, shelter and space.
Survival of fittest/ Natural selection:  Only those individuals which have favourable variations survive and reproduce while others not suited by the environment perish away.  Thus nature exercises its selection and only those individuals that are ‘fit’ to survive and reproduce successfully.
Origin of Species/Speciation:  This continuous process of variation and natural selection will ultimately result in elimination of certain individuals; while others will gradually establish.  In this process new characters, which are good, will set in.  Thus new species may be produced in due course of time.

Mechanism of Evolution: 
Hugo deVries believed that it is mutation which causes evolution and not the minor variations (heritable) as Darwin said.  Mutations are random and directionless while Darwinian variations are small and directional.  Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it Saltation (single step large mutation).

Hardy-Weinberg Principle:
According to this law, if all the factors / conditions remain constant, the frequency of particular genes and their alleles will remain constant in a population of sexually reproducing organisms from generation to generation. 
The difference between the observed frequencies of alleles and those predicted by Hardy-Weinberg Principle indicates the degree of evolutionary change.  Evolution occurs when the genetic equilibrium is disturbed. 

Factors affecting Hardy-Weinberg Equilibrium:
Gene migration / Gene flow
Genetic drift
Mutation
Genetic recombination
Natural Selection

Examples of Natural Selection:

1.Industrial melanism.     
                A case of natural selection was seen in Great Britain in a peppered moth (Biston betularia).  This moth had two forms: grey colour and black colour (Carbonaria).  In the early part of the nineteenth century only the grey coloured forms of moths were present; the dark forms were rare.  The grey coloured moths were seen on the tree trunks covered with lichens and so they were able to escape from their enemies. Later on, due to the development of industries the lichens were killed and the tree trunks looked dark due to the deposition of industrial soot.  Birds, now were able to spot these moths and feed upon them.  So the grey coloured moths were eaten by the birds and the dark coloured moths escaped from the birds. Then now the coal is replaced by the industries and oil and electricity is used.  This has reduced the soot production and ultimately less deposition of soot on the tree trunks.  These tree trunks have, now, again become grey in colour.  Consequently, grey coloured moths have again increased in number.  This example clearly brings out the action of natural selection.

2.Resistanceof mosquitoes to pesticides.
When DDT was introduced to control mosquitoes it was tremendously successful.  Most of the mosquitoes were sensitive to DDT and were therefore killed.  In that population of mosquitoes, few mosquitoes became resistant to DDT and survived.  They multiplied and now almost total population of mosquitoes became resistant to DDT.  

                Hence the principle of natural selection shows that the chemical insecticides can remain effective only for a limited period.  

Adaptive Radiation:
The 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. Ex. Darwinian Finches, Australian Marsupials.

A Brief Account of Evolution:
About 2000 million years ago the first cellular forms of life appeared on earth.  Some of these cells had the ability to release O2.
Slowly single-celled organisms became multi-cellular forms and by the time 500 mya, invertebrates were formed and active.
Jawless fish evolved around 350 mya.
Organisms started to invade from water to land.  Fish with stout and strong fins could move on land and go back to water. These fishes evolved into the first amphibians
Later, these amphibians evolved into reptiles. They lay shelled eggs.  Then reptiles of different shapes and sizes dominated on earth (dinosaurs). 
Some of the reptiles evolved into birds and later some of them to mammals.  Mammals were viviparous and more intelligent in sensing and avoiding danger at least.

Origin and Evolution of Man:
About 15 mya, primates called Dryopithecus and Ramapithecus were existing.  They were hairy and walked like gorillas and chimpanzees.  Ramapithecus was more man like and Dryopithecus was more ape-like.
Two mya, Australopithecines probably lived in East aftrican grasslands.  Evidence shows that they hunted with stone weapons but essentially ate fruits. 
Fossils of first human like being the hominid were found and their brain capacity were between 650-800cc, they were called as Homo habilis. They did not eat meat.
Fossils discovered in Java 1891 revealed the next stage, i.e., Homo erectus about 1.5 mya and had a large brain around 900 cc and they ate meat.
Neanderthal man with a brain size of 1400 cc.  They used hides to protect their body and buried their dead. 
Homo sapiens arose in Africa and moved across continents and developed into distinct races.
During ice age between 75,000-10,000 years ago modern Homo sapiens arose.