Theories of evolution

Theories of evolution

1. Lamarck theory

   • Proposed by
     • Jean Baptiste de Lamarck in 1809
   • is based on
     • Use and disuse of organs
       • Produced by
         • New habits and changes in environment
           • This produce
             • The form of organs
             • The structure of organs
             • The function of the organs
       • Use
         • Make organs more efficient
       • Disuse
         • Cause the degeneration and ultimate disappearance
     • New needs
       • Produced by
         • Changes in the environmental factors like
           • Light
           • Temperature
           • food
           • air
           • Migration
           • Medium
           • Causing that species
             • Changes Habits
             • Change behaviour
             • Develop new organs
             • Increase size
               • In order to survive
               • examples
     • Speciation
       • In every generation
         • New character are Acquired and transmitted
           • To new generations
             • Accumulationg the new characters until
               • a new specie is formed
                 • By a gradual process
     • Inheritance of acquired characters
       • The changes produce in an organism
         • would be
           • Transmitted to the offspring
             • to
               • Reproduce
               • Survive new environments
               • Fit new conditions
   • First comprehensive theory of biological evolution
   • It´s not accepted
     • Because studies show is incorrect

2. Darwin Theory

   • Proposed by
     • Charles Darwin and A.R Wallace
       • State that every population has built in variations in their characters
         • All organisms
           • Descendents of previously existing forms of life
       • Both conclude that natural selection is related and determined by the environmental changes
   • Main Postulates are
     • Natural Selection
       • States that
         • Nature
           • Select those individuals that
             • Have useful continuous variations
               • To survive
             • That are best adapted to the environment
             • unfit with the environment
               • To die
     • Variations
       • Are generally two types
         • Continuous variations
         • Discontinuous variations
           • Can be neutrl, harmful or useful
             • According to their effects in survival chances
     • Struggle for existence
       • Competition between individuals having similar requirements
         • Divides in three types
           • Intraspecific
             • Between the members of same species
           • Interspecific
             • Between the members of different species
           • Extra specific
             • Between living organisms and adverse environmental factors
     • Limited food and space
       • States that
         • Food increases arithmetically
           • Producing limiting factors
             • Limited food
               • Not allow a population to grow indefinitely
             • Limited space
     • Geometric Increase
       • Says that
         • Populations tend to multiply geometrically
           • Every specie can increase within a few generations
             • Provided all survive and repeat
         • Reproductive powers of living organisms are much more than required
           • Even slow breeding organisms
     • Inheritance of useful variations
       • Selected individual by natural selection
         • Pass thier useful variations to offsprings
           • So born to fit and survive
     • Speciation
       • useful variations accumulate
         • Turning individuals into new species
           • In a gradual Process and changes

3. Mutation theory

   • Proposed by
     • Hugo de Vries
       • Used the term mutation for
         • Phenomenom of appearance of sudden heritable changes
   • Says that
     • Evolution is a continuous and jerky process in which there is a jump from one specie to another
       • Producing that new species arises
         • From pre- existing ones in a single generation
           • Not in a gradual process like the other theories
           • But
             • Mutation is random, so the evolution is also random
       • The mutations in organisms were called new and separated species
     • Populations are pre-adapted
       • adaptations don´t necessarily comes from

4. Synthetic Theory

   • Recognize five main factors
     • Gene Mutation
       • Are invisible changes in chemical nature (DNA)
         • Divided in three types
           • Deletion
             • Loss of one or mor nucleotide pairs
           • Substitution
             • Replacement of one or more nucleotide pairs by other base pairs
           • Addition
             • Gain of one or more nucleotide pairs
         • That cause
           • Changes in the sequence of amino acids
             • Changing
               • The nature and phenotype of proteins
     • Changes in structure and number of chromosome
       • May be
         • Euploidy
           • Gain or loss of one or more genomes
           • Can be
             • Haploidy
               • Recessive genes express in the same generation
             • Polyploidy
               • Tetraploidy
                 • Most common
               • Provides greater genetic material for mutations and variability
         • Aneuploidy
           • Gain or loss of one or two chromosomes
           • Can be
             • Hypoploidy
               • Tetrasomy
                 • Gain of two chromosomes
               • Trisomy
                 • Gain of one chromosome
             • Hyperploidyl Hypoploidy
               • Monosomy
                 • Loss of one chromosome
               • Nullisomy
                 • Loss of two chromosomes
     • Genetic recombination
       • New combination of genes
         • Produced by
           • Change fusion of gametes during fertilization
           • Chance arrangement of
             • Bivalents at the equator during methaphase
           • Crossing over
     • Natural selection
       • Operates
         • Through differential reproduction
           • The best adapted individuals would reproduce and produce more offsprings
             • Until the genes become predominant
               • Progressive changes
             • Their characteristics are
               • Which have better chances of sexual selection due to development of some bright coloured spots on their body e.g. in many male birds and fish.
               • Those who are able to overcome the physical and biological environmental factors to successfully reach the sexual maturity.
               • Mostly those individuals which are best adapted to the environment
           • Less adapted ones would produce fewer offsprings
         • Through comparative reproductive succes
     • Reproductive isolation
       • Isolation mechanism
         • Any factor which reduce the chance of
           • Interbreeding between the related groups of living organisms
       • Allow the accumulation of variations leading to speciation
         • By
           • Preventing hybridization
       • Helps in evolutionary divergence
   • Proposed By
     • Ernst Mayr
     • J.S. Huxley
     • H.J. Muller
     • S. Wright
     • R.A. Fisher
     • R. B. Goldschmidt
     • Th. Dobzhansky
     • J.B.S. Haldane
     • G.L Stebbins

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