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Eyes: How They Work, Anatomy and Common Condition

 The eye is a complex sensory organ that allows us to see the world around us. The eye works by gathering light from the environment and converting it into electrical signals that can be interpreted by the brain. The basic structure of the eye includes the cornea, iris, pupil, lens, retina, and optic nerve. The cornea is the transparent outer layer of the eye that helps to focus incoming light. The iris is the colored part of the eye that regulates the amount of light that enters the eye through the pupil, which is the black circular opening in the center of the iris. The lens is a clear, flexible structure located behind the iris that helps to focus light onto the retina. The retina is a thin layer of tissue that lines the back of the eye and contains photoreceptor cells called rods and cones. These cells convert light into electrical signals that are sent to the brain via the optic nerve. The rods are responsible for the low light vision and detecting motion, while the cones are resp
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LAMARCKISM (Theory of organic evolution)

Organic evolution is the changes in flora and fauna during the course of time. But when we see in our surrounding we didn't observe any changes because these changes are very small so we can't determine it but changes is taking pace in every moment of time and in previous post we see the evidences in favour of organic evolution and today we going to discuss about the theories of organic evolution. There were many theories given by various scientists for organic evolution, some of them we discuss here today.

 LAMARKISM / Theories of inheritance of acquired  characters:-


Jean Basptiste de Lamarck (1744 - 1829) was a French naturalist who proposed the first logical theory of evolution in his book Philosophie Zoologique (1809)

Basic concepts of Lamarckism:-


  1. Internal vital forces : Due to the presence of some internal vital forces all organisms have the tendency to increase in size of their organs or entire body
  2. Effect of environment and new needs : Environment influences all type of organisms. Changing environment gives rise to new needs. New needs or desires produce new structures (doctrine of desire / appetency) and change habits of the organism.
  3. Use and disuse of organs : If an organ is constantly used over generations, it would be better developed whereas disuse of organ results in its degeneration (vestigial organs).
  4. Inheritance of acquired characters : During the life time of an organism, new characters develop due to internal vital forces, effect of environment, new needs or use and disuse of organs. All these acquired characters are inherited from one generation to another. By continuous inheritance through several generations, the variations are accumulated up to such extent that they can give rise to new species.

Some Examples in favour of lamarckism :-


  1. Long neck and forelimbs of giraffe : Lamarck gave the example of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks. As they passed on their acquired character of elongated neck to succeeding generations, Giraffes, slowly over the years came to acquire long necks.
  2. Aquatic birds stretched their toes and developed web.
  3. Snakes lost their legs.
Lamarck had said that evolution of life forms had occurred but driven by use and disuse of organs. Nobody believes  this conjecture any more.

Criticism of Lamarckism :-

  1. Weismann's Theory of Continuity of Germplasm : Weismann proposed this theory by performing  an experiment on rats. He cut off the tails of rat for as many as 22 generations and allowed them to breed, but tailless or reduced tailed rats were never born. On the basis of this experiment he concluded that there are two types of protoplasms are present in an organism i.e. germplasm and somatoplasm. And there is a continuity of germplasm and the variations influencing the germ cells are only inherited but the somatoplasm is not transmitted to the next generation, hence it does not carry variations to next generations.
  2. Boring of ear pinna and nose in Indian women is never inherited to the next generations.
  3. Chinese women used to wear iron shoes in order to have small feet, but they still have normal feet
Hence, after seeing the theory of continuity of germplasm the lamarckism theory was not accepted at all but after some time the followers of Lamarck modify the lamarckism theory in Neo Lamarckism. According to Neo Lamarckism, "Changing environment may create some physical and chemical changes in somatoplasm of organisms, which may affect their germplasm also and such acquired characters can inherit."

Many experiments were also done to support the theory of Lamarck which are not convincing and satisfactory

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