Evolution

Biological evolution


  • There were 3 conditions for the origin of life
    ⇒ continuous supply of replicators
    ⇒ copying error during replication
    ⇒ system must have required a continuous supply of free energy.
  • Biological evolution started with the formation of pre/protobionts which are non living structures that led to the formation of first living cells from which the more complex cells have evolved.
  • The 2 prebionts are
    Oparin ⇒ coacervates [aggregation of colloidal particles in liquid phase that consists of carbohydrates, proteins, lipids and nucleic acids surrounded by a non-biological membranes
    Sydney Fox ⇒ Micro spheres [Microscopic membrane bound spheres formed when protenoids are boiled in water and allowed to cool. Protenoids are produced by dehydration synthesis of amino acids at 180°C]
  • Oldest known fossil ⇒ Stromatollites [sheet formed over sedimentary rocks which contained a species of Blue green Algae, called Archaeospheroides barbetonensis].
  • Evolution of modes of Nutrition
    (heterotrophs)
              ↓
    (Chemoheterotrophs)
              ↓
    (Autotrophs)
              ↓
    (Chemoautotrophs)
              ↓
    (Photo auto trophs) - Eg. Cyanobacteria
  • As the number of photoautotrophs increased, O2 was released in the sea and atmosphere which is termed as O2 revolution.
  • As O2 accumulated in atmosphere, the UV light changed some of the O2 into Ozone.
    2O2 + O2 → 2O3
  • Origin of Eukaryotes is of two types
    ⇒ Symbiosis [Margulis]
    ⇒ Origin by Invagination
  • Symbiotic origin :
    ⇒ Predator host cell  +  aerobic bacteria  ⇒  Eukaryotic animal cell
                              [Contributing Mitochondria]
    ⇒ Predator host cell + aerobic bacteria + cyanobacteria  ⇒ Eukaryotic plant cell.
                                     [mitochondria]      [chloroplast]
  • Three domains of life [Carl Woese]
    ⇒ Eubacteria
    ⇒ Archae
    ⇒ Eucarya
  • Finally, it is concluded that the life originated from ocean.
    ⇒ Evidences for organic Evolution
  • The study of fossils is called as Palaeontology.
    ⇒ Leonardo da Vinci [The Father of Palaeontology]
    ⇒ George Cuvier [The Founder of modern Palaeontology]
  • The fossils of spores, Pollen grains and other microscopic structures are called micro fossils (or) Palyno fossils.
  • Age of the fossils can be determined by following methods
    ⇒ Clock of the rock method / Radioactive clock
    ⇒ Radioactive carbon method
    ⇒ Potassium - argon method
  • The first geological time scale was developed by Gioranni Avdesina. The history of the earth has been divided into a number of major divisions called eras, which are sub divided into periods. The modern periods are further divided into epochs.
  • The fossil record contains some transitional link forms called missing links [also called as connecting links].
    Eg. Archaeopteryx [connecting link between birds and reptiles]
  • Evolution of Vertebrates :
    Ostracoderms
             ↓
    Acanthodians
             ↓
    Placoderms
  • Evolution of horse :
    Eohippus [renamed as Hyracotherium]
          ↓
    Mesohippus [Intermediate horse]
          ↓
    Merychippus [ruminating horse]
          ↓
    Pliohippus [first, one toed horse]
          ↓
    Equus [modern horse]
  • The organs which have the same fundamental structure but are different in functions are called Homologous organs
    Eg. ⇒ Forelimbs of frog, pigeon, lizard, bat, whale, horse, human
    Mouth parts of cockroach, mosquito, honeybee and butterfly
    ⇒ Thorn of Bougainvillea and Tendrils of cucurbita
    ⇒ Testis and ovary
    ⇒ Radish and carrot
    ⇒ Potato and ginger
  • Homology observed amongst the molecules are called as molecular homology.
    Eg. Proteins found in the blood of man and ape.
  • Homologous organs show divergent evolution with adaptive radiation.
  • The organs possessing similar functions but different in structure and origin are called as Analogous organs.
    Eg : ⇒ Wings of insect and wings of a bird / bat
    ⇒ Hands of Human and Trunk of an elephant
    ⇒ Stings of honey bee and scorpion
    ⇒ Fins of fishes and flippers of whale
    ⇒ Eye of octopus and cat
  • The presence of these analogous organs indicate a similar adoptational functional structures in unrelated groups is called as convergent evolution.
  • The organs which do not perform any function in the body, that are present in the reduced form but correspond to the fully developed functional organs of related animals are termed as vestigial organs
    Eg ⇒ nictitating membrane (plica semilunaris)
    ⇒ External car (pinna)
    ⇒ Vermi form appendix
    ⇒ Caudal vertebrae
    ⇒ Third molars
    ⇒ Hair on body
    ⇒ Male - nipples.
  • The organisms which possess the characters of 2 different groups are called connecting links.
    Eg ⇒ Euglena [b/w plants and Animals] ⇒ Echidna / platypus (egg laying mammals)
    ⇒ Peripatus [annelida and Arthopoda] [b/w reptile and mammals]
  • The reversal of an ustral characters which had either disappeared is called as Atavism. Eg. Tendency of moving pinna, long dense hairs, short fail in some babies.
  • Evolution can also proved by Emryological studies, especially by Baer's law, which states that, during embryonic development, the generalized features [Brain, spinal cord] appear first and then the specific features [hair, legs] appear.
  • Baer's law was modified by Ernst Haeckel as Ontogeny repeats phylogeny. where ontogeny is Evolutionary relationship, which means that the organism during its embryonic development resembles its ancestors nature.
  • Example : Development of the frog includes Tadpole larval stage which resembles a fish.
  • The organism repeating its ancestral history during its development is called as Biochemical recapitulation. Eg. Fishes are Ammonotelic and Tadpoles are also the same, whereas frogs are ureotelic. which could prove that frogs arise from fishes.
  • Physiological evidence / Biochemical evidence such as presence of blood, ATP, Trypsin, nucleotides and etc in all the various form of animals had strongly proven than evolution have taken place.

Watch this video for the topic from 1:18 to 12:40

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