Evolution, Std-10

 
Before studying about evolution we will discuss about traits and their types.
* Traits
:- Characteristics of the organisms are known as traits. It is of two types
a. Acquired Traits, and
b. Inherited Traits.
1. Acquired Traits
:- A trait of an organism which is not inherited but develops in response to the environment is called an acquired trait.
:-> It can not be passed from parents to their progeny.
E.g. The cut tail of mice( rat ) is an acquired trait which never passed on to their progeny.
              This is because cutting of the tail of mice does not change the genes of their reproductive cell or gametes.
2. Inherited trait
:- A trait of an organism which is caused by a change in its genes ( DNA) is called an inherited trait.
:- It can be passed from parents to progeny.
:- E.g. Eye color, hair color, free or attached earlobe etc.
*Evolution
:- Derived from a Greek word 'evolvere' means unrolling or unfolding of nature.
:-> This term was proposed by Herbert Spencer. 
:-> The sequence of gradual changes which take place in the primitive organisms over millions of years in which new organisms are produced, known as evolution.
:-> In other word :-
                                    Evolution is change in the heritable characteristics of biological populations over successive generation.
*Types of Evolution
a. Organic Evolution/Biological evolution
b. Inorganic Evolution
1. Organic Evolution
:-> The changes in the heritable characteristics of biological population over successive generation is called Organic evolution.
:-> This evolution among living organisms only.
2. Inorganic Evolution
:- A type of evolution in which changes occur in inorganic substances is called inorganic evolution.
*Evidences for Evolution. 
a. Morphological evidence/Homologous organs.
b. Embryological evidences/Analogous organs.
c. Fossils/Fossils record.

A. Homologous Organs
:- Those organs which have the same basic structure but different functions are called homologous organs.
:-> It is also known as morphological evidences.
:-> These organs of different animals provide evidences for evolution.
:- E.g. Forelimbs of human ( used for grasping , forelimb of lizard( running), and forelimbs of frog(shock absorber).
:-> These organs derived from same ancestor who had the basic design.
B. Analogous Organs
:- Those organs which have different basic structure but have similar appearance and perform similar functions are called analogous organs.
:-> These organs provide the evidences for evolution.
:- E.g. Wing of insects and wing of birds.
C. Fossils
:-> The remains of dead animals and plants that lived in the remote past are known as fossil.
:-> These Fossils also provide evidences for evolution.
:-> e.g. Archaeopteryx ( a connecting link between reptiles and bird ), Fossils of Ammonite, Trilobite, Tree trunk, Fish( Knightia ) & Dinosaur skull.
Note:- Palaeontology:- A branch of science which deals with the study of Fossils is called Palaeontology.
:-> Fossils provide direct and most reliable evidences for evolution.
:-> These are obtained by digging into earth.
:-> The age of fossils can be estimated in two ways :-
a. By relative method. 
b. By carbon dating method. 

a. By relative method
:- This method works on digging into the earth.
:-> Depth determine the age of fossils.
                                                                    The fossils which we find in layers closer to the surface of earth are more recent whereas the fossils found in the deepest layers of the earth are oldest ones.
b. By Carbon dating method
:- In this method isotopes of carbon are used.
        It is done by detecting the ratios of different isotopes of the same element ( I.e carbon ) in the fossils materials.
Note:- All living organisms contain Carbon-14 atoms (radioactive ).

*Darwin's Theory of Evolution or Darwinism 

:- Full name of Darwin - Charles Robert Darwin ( 1809-1882 ).
:-> He gave theory of evolution in his famous book - The Origin of Species in 1859.
:-> It is also known as The theory of Natural Selection (why)👇
                          Because it suggests that best adapted organisms are selected by nature to pass on their traits to the next generation.

* Postulates of Darwinism
:->Darwin stated that-
1. Within any population, there is natural Variation, some individuals have more favourable variations than others.
2. All species produce large number of offsprings but populations remain fairly constant naturally(how)👇
                                             This is due to the struggle between members of the same species and different species for food, space and mate(partner).
3. The struggle for survival within population eliminates the unfit individuals.
4. The fit individuals possessing favourable variations survive and reproduce. ( This is known as Natural selection).
5. The individuals having favourable variations pass on these variation to their progeny.
6. The variations when accumulated over a long period of time leads to the Origin of a New Species.
 Note:- Darwin didn't explain how the variations arise.
* Neo-Darwinism Or Synthetic theory of evolution. 
:- The Darwinism was remodified by Hugo de Varies.
:-> He added few postulate in it.
1. Genetic Variation or gene variability
 ( Variations in organisms caused by gene).
2. Natural selection - only well adapted organisms selected by nature.
Speciation
:- Formation of new species is called speciation. OR
:-The process by which new species are developed from existing ones is called speciation.
*The important factors which could lead to the rise of a new species are the following:-
1. Geographical Isolation of a Population 
:-> It is caused by various types barriers like - Mountain ranges, Rivers and Seas👇
                                                               It leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
2. Genetic Drift
:-> It is caused by drastic changes in the frequencies of particular gene by chance alone.
3. Variations caused in individuals due to natural selection.

*Evolution by stages 
:- Evolution that occurs at different stages in life over many generation is called evolution by stages.
E.g. 1. Evolution of eyes ( Planaria ), Insects.
   2. Evolution of feathers.
*Evolution by Artificial Selection
 e.g. Wild Cabbage
               👇👇
          1. Cabbage
          2. Broccoli
          3. Cauliflower
          4. Kohlrabi ( German turnip)
          5. Kale

   *HUMAN EVOLUTION
:-  Taxonomic position of the humans.
                 👇
:-  Kingdom - Animaliya
     Phylum -    Chordata
     Subphylum - Vertebrata
     Class -   Mammalia 
     Order-  Primata
     Sub-order- Anthropoidea
     Super family - Homonoidae
     Family -  Hominidae
     Genus -   Homo
     Species - Sapiens
:-> Scientific name - Homo sapiens
:->  Evolved about 20 million years ago.
:-> Ancestors - Dryopithecus and
    Ramapithecus.
:-> Place of Origin - East  Africa, Asia and Europe { centre of Origin was in Africa }.
:-> A couple of hundred thousand years ago some of human ancestors left Africa and spread across the planet { From Africa to West Asia to Central Asia, Eurasia and so on..
:-> It was studied by the using of various methods with the help of tools like - time dating, Excavation, studying fossils and determining DNA sequences.
:-> It is believed that Man( Homo sapiens) evolved about 500000 - 750000 years ago.
:-> The Homo sapiens evolved further to the Neanderthal man followed by the Cromagnon man and further the Modern man.

*Origin of Life on The Earth
:-> Theory related to the Origin of life on earth was proposed by J.B.S Haldane in 1929.
:-> According to him - Lives have developed from the inorganic molecules such as CH4 ( methane ), NH3 ( ammonia ), H2S ( hydrogen sulphide ), which were present in the sea.( due to action of lightening ).
:-> Or you can say according to this theory - Life originated in the Sea water.
:-> Haldane theory was proved/confirmed experimentally by Stanley L. Miller & Harold C. Urey in 1953.
:-> They assembled an apparatus to create an early earth atmosphere, consisting some gases like CH4, NH3 & H2S.
:-> This experiment was conducted at temperature just below than 100°c .
:-> At the end of one week it was found that 15% of carbon ( CH4 ) had been converted into simple compounds of carbon I.e Amino acids 👉 It makes protein molecule in living organisms.