Theory of Evolution: From Prokaryote to Eukaryote And Its evidences

 What is evolution?

    Evolution is a process in which organisms are changed from over time. In other words evolution is refers to a phenomena in which an organism develops into another organism.

Theory of evolution vs Theory of special creation:

    There are two types of scientist; Creationists who believe in god and evolutionists who believe in evolution.
  • Creationists believe that there is divine force who create all living organisms, in their present forms. This theory is known as theory of special creation. This theory was given by Carolus Linnaeus. He classified organisms into groups according to genus. He believed that species were permanent creation.
  • Evolutionists believe that organisms are transform their genetic make-up and those organisms can survive who can change and suited with environment this belief is known as natural selection. For example dinosaurs are extinct because food chain had collapsed. This theory was given by Charles Darwin.
Scientists have proposed different explanations for the origin of life, but the theory of evolution by natural selection is the widely accepted scientific explanation.

Evolution from prokaryote to eukaryote

Hydrothermal vents hypothesis:

     It is thought that life was firstly appear in the form of single prokaryotic cell. It was the origin of life. The life was originate from hydrothermal vents. Hydrothermal vents are hot water bodies found in the deep of ocean, In these vents reaction occur and form a prokaryotic cell. Life was appeared approximately 3.5 billion years ago.

Prokaryotic cell: 

    Prokaryote comes from Greek word prokaruon; Pro means before and karuon means nut(nucleus). They lack membrane bounded organelles. Nucleus is not clear and DNA floating in cytoplasm. First prokaryote was archaeobacteria which can tolerate temperatures up to 120°C.
Prokaryotic cell

Photosynthesis and formation of ozone layer:

    Life should need nutrients. The nutrients was limited for early life. Photosynthesis was a great need for life. First photosynthetic organism use hydrogen sulfide(H₂S). These photosynthetic reaction produce oxygen and life become changes slowly.
This oxygen released in atmosphere and ozone layer has built up. It is a protective layer which helps in maintain Earth's temperature because it stop UV rays to reach surface. Ozone layer was built about 420 million years ago. 

Eukaryotic cell: 

    Eukaryote comes from Greek word eukaryon eu means true and karyon means nut(nucleus). It means that they have membrane bounded true nucleus. 
Eukaryotic cell

Endosymbiont hypothesis:

    Approximately after 2.5 billion years a large anaerobic bacteria engulfed a small aerobic bacteria, which then live symbiotically. Mitochondria and chloroplast has their own DNA and they might be live independently. Mitochondria is cell organelle which use aerobic respiration to form ATP(energy). Bacteria engulfed mitochondria, it brought the advantage of aerobic respiration to the host. This hypothesis known as Endosymbiont Hypothesis. This hypothesis was proposed by Lynn Margulis. 
Heterotrophic cell might be produced when cyanobacteria(photosynthetic bacteria) was engulfed by prokaryote. 

Production of flagella:  

    Flagella(thread like structure help in the movement of cell) may have formed when spirochetes(spiral-shaped bacteria) was ingest by prokaryote.
With the passage of time single cells evolve in multicellular organisms. The organisms become more complex. They change themselves as well as environment according to their needs. 

Evidence of evolution:

     Darwin's theory of evolution is based on fossil record, biogeography and anatomy. As biology progressed there are many evidences some are described below:

Fossil record:

    Fossils are remains of organisms found in sand, ice and mostly sedimentary rocks. Fossil records have great evidence in the favor of evolution. Evidences from biochemistry, cell biology and molecular biology places prokaryotes as ancestor of all living organisms. There are gradual changes in size and shape of organisms. Fossil records proposed that organisms have been change for survival. 

Biogeography:

    Geographical distribution firstly give idea of evolution to Darwin. Islands have many species of plants and animals are related to those organisms lives on mainland. For example armadillos only live in America. Biogeography predict that armadillos are evolved from giant mammal glyptodon.

Comparative anatomy:

    Anatomical similarities between species support theory of evolution. For example forelimbs of humans, bats, monkeys and whales have same structure but different functions. This is known as homologous structures. This similarity support that they have common ancestor. The foreleg of mammals have same function and different structures. This is known as divergent structures.

Comparative molecular biology:

     Molecular biology is a branch of biology which deals with biomolecule such as proteins, carbohydrates and nucleic acid. Molecular biology of organisms is another evidence of evolution. For example all organisms have DNA and RNA. Their cells are compose of protein. It means that all organisms may be originate from common ancestor which has same molecular biology.
    

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