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Evolutionary of Organisms

There is no doubt that life had a beginning on Earth. So had earth an origin. How did they originate are the domains of conjecture, of course supported by various evidences. We do not have a time machine to go back in time and observe the two types of origins. It is clear that there was an origin of earth, origin of life and evolution of living organisms.

Evolution

Evolution is revealing of hidden potentialities that bring about an orderly change from one condition to another.

Stellar or cosmic evolution deals with the changes that bring about birth growth and death of stars and planets.

Inorganic evolution is the sequence of changes that occur in the inorganic matter and its elements.

Organic evolution, by Spenser 1852, is the formation of new types of organisms from the pre-existing ones through modifications. Evolution is therefore, often called as descent with modifications by Darwin, 1859.

As the time passes by, there are changes in the properties of population of organisms or group of such population. These changes pile up and give rise to new forms. The new forms possess a common ancestor.

Lineage is the evolutionary sequence arranged in a linear order from a common ancestor to the descendent group. The number of evolutionary trends present in any lineage is equal to the number of characters evolving. They may be progressive or retrogressive. With time, two or more lineages diverge from a common lineage.

Studying differences and similarities in adaptive and non-adaptive characteristics of organisms can give sufficient information about their evolution. Rather significance of various features and functions of living organism cannot be properly appreciated without knowing their ancestry.

According to Theodosius Dobzhansky, (1973) ‘Nothing in biology makes sense except in the light of evolution’.

Evolutionary History of Organisms:

As far as known life exists only on earth, though there is the possibility of its presence elsewhere as well. Methane, which has helped develop life on earth, occurs on Jupiter, Saturn and interstellar space. Water is believed to be present on Mars, our moon, moon Europa of Jupiter and moon Titan of Saturn.

There are several theories about the origin of earth and various evidences about the origin and evolution of life on earth, which proves that life on earth has evolved from the pre-existing ones.

Stages of Evolution:

The process of evolution has developed over millions of years. The origin of a new species and thus formation of new lineages occurs gradually in stages. It is said that life has existed on the Earth approximately 3.5 billion years ago, the first to stages of evolution took comparatively large period of time to get evolved. The evolution first started with molecular level, synthesizing the bio molecules which later preceded as follows.

Stages of Evolution : Development of Unicellular Prokaryotes

Development of unicellular prokaryotes is considered as the first step of evolution. The earliest types of cells were believed to be 'prokaryotes', free living cells without  nucleus. These cells possess circular DNA which is found in cytoplasm. Cell structure and other activities are very simpler in prokaryotes.

E.g. bacteria

Stages of Evolution : Development of Eukaryotic Cells

When there was availability of oxygen 'Eukaryotes' developed between one and two billion years ago. These cells possessed nucleus. Eukaryotes have their genetic material that is DNA within the nucleus which is 10 to 1000 times more than that found in prokaryotes. Eukaryotic cells were found to be more complicated and well organized than that of their precursors prokaryotes.

Stages of Evolution : Begining of Cambarian Period and Development of Multicellularity

After development of prokaryotes and eukaryotes the process of evolution took speed. Some 600 million years ago a Cambarian period began with the development of more organized structured organisms having tissue level and organ level of organization. Organisms with more or less developed organ system, possessing skeletons, hard shells, carapaces appeared. The first fish and the vertebrates appeared.   Just before 10 million years, the first creatures evolved which resembled human beings later the development in brain occurred with the development in brain and its size the first true humans emerged.

Stages of Evolution : Invasion on Lands

Phytoplankton were the only plant species which later started colonizing lands; then the arthropods evolved which were also land organisms. with the development of amphibians the the winged insects arose too. Then the trees, reptiles, dinosaurs evolved. Then emerged the mammals. Which later was preceded by origin of first birds, first flowers. After this period the primates (the ancestors apes and humans) came into existence.

evolution

Evolution and Diversity

After invasion on lands, the major evolution took place was in intelligence which can not be counted as biotic. The stages discussed above are the major biotic stages of evolution which occurred very slowly and step wise process from simple single, unicellular to most complicated , multi cellular organisms.

Evolution of Man

Theory of Evolution of Man:

     The word evolution can be derived from the Latin word evolvere which means unroll or unfold. Theory of evolution of man is the process by which living beings change as one generation succeeds to another. Evolution is a tremendously slow process. The theory of evolution of man includes the micro evolution, nature selection and speciation.

Evolution of Man:

        There is a greater diversity of human forms and features across the planet. For a considerable period of time, biologists debated on the possibility of evolution of these apparent human forms in different ways, although human evolution has been traced by using the same tools like fossil records, excavation, carbon dating and determining DNA sequence.

Principles of Evolution of Man:

    The concept of evolution theory has on three major principles. They are

       1)  Micro evolution

       2)  Nature selection

       3)  Speciation

  Micro evolution:

       It is built by the mutation in genetic sequence in the organisms. Mutations are randomly occurred in the naturally errors in reproduction progression in environmental process such as the chemicals or the radiations.

  Nature selection:

       Nature selection in theory of evolution is the process in which the species can survive in the particular place fit for the genetic information. It is for the survival of the particular gene for fittest.

  Speciation:

       Speciation is the process that when a member of species mutate at a particular place for the longer time to breed with other members of the same species. The new species becomes an isolated community for the population. The gene in the new population is isolated for the previous species group. The speciation in theory of evolution contains four types of mechanism. They are accumulation of variation, physical barriers, genetic drift and migration.

  • In accumulation of variation, two individuals are identical except the identical twins. The difference is observed in various individuals of species are called variation.
  • Physical barriers may develop within a species dividing it into two or more isolated population.
  • Genetic drift is change by elimination or change by fixation of gene for a certain trait in a small population without having its selection benefit.
  • Migration means some individuals of a species reach, by chance an isolated island which is widely separated from the main land.

  

Evolution by Stages:--->

Organic Evolution:

        Let us learn about the definition of organic evolution. A gradual genetic difference in a set of living beings to generate new forms is called the organic evolution. Lot of generations has to exceed through small changes before the change occurs in that organism. The plants and animals in the environment are evolved from their ancestor. The definition of organic evolution process made an organism slight change from their ancestor.

Evolution by Stages:

     The organic evolution process cannot occur in a define single DNA change. The following stages are takes place in the evolution.

  1)  Evolution of eyes:

            The eye is the most important organ in all organisms. The eye is one of the difficult organs that cannot be created in a single DNA. Eyes are first developed in the planaria. Rudimentary eyes in the planaria are just as like as photo sensitive eye spot. The eyes that are present in the insects, vertebrates are as the analogous organs. These are developed by bit by bit for their adaptation.  

  2)  Origin of feathers:

           Some of the changes are useful in one property to start with that can be useful later for particular different functions. Feathers are first developed in the dinosaurs. It is for protecting the animal in cold weather. Later the feathers are developed for birds also. This organic evolution includes that the birds are closely related to the dinosaurs.

  3)  Artificial selection:

           Artificial selection includes the variations takes place in randomly all living organisms. The plants and animals are trying to improving them. This type of the improvement is for selecting the individuals which have the useful characteristics and aloe them to breed in nature. This kind of process is called as artificial selection.

 

Evidence for Define Organic Evolution:

      There are various changes that are takes place in the organisms to evolve in the new form of the organisms. The following sources are providing the define evidence,

          1)  Homologous organs

          2)  Analogous organs

          3)  Fossils

      The structures with general origin but with the various functions are called as the homologous. It gives the details about the difference in the bone structure. Analogous organs provide the details about the changes in the feathers of the birds. Fossils give the details about the living organs structure.


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