Heredity and Evolution

Heredity and Evolution

Evolution

Heredity: - Heredity is the transfer of biological characters from one generation to another via genes.

Transcription: - In transcription the DNA sequence of a gene is copied out to form an RNA molecule.

Translation: - The mRNA is decoded to build a protein that contain a specific series of amino acids. This process is called Translation

Triplet Codon: - The code for each amino acid consists of three nucleotides. It is called as ‘triplet codon’.

Translocation: - The movement of ribosome from one end of mRNA to other end by the distance of one triple codon is called as translocation.

Evolution: - Evolution is the gradual change occurring in living organisms over a long duration. This is a very slow-going process through which development of organisms is achieved.

Theory of Evolution:

According to this theory, first living material (protoplasm) has been formed in ocean. In due course of time, unicellular organism was formed. Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed. All those changes were slow and gradual.

Evidences of evolution

1) Morphological Evidences: - Similarities in superficial character

2) Anatomical Evidences: - Similarities in bone structure.

3)Vestigial Organs: - Degenerated or underdeveloped useless organs of organisms are called as vestigial organs.

4) Paleontological Evidences: - Study of fossil.

5) Connecting Links: - Some plants and animals show some morphological characters by which they can be related to two different groups; hence they are called as ‘connecting links’.

6)Embryological Evidences: - Comparative study of embryonic developmental stages of various vertebrates. All embryos show extreme similarities during initial stages and those similarities decrease gradually. Similarities in initial stages indicate the common origin of all these animals.

Darwin’s theory of natural selection

Darwin says that all the organisms reproduce prolifically. All the organisms compete with each other in a life- -threatening manner.

 In this competition, only those organisms sustain which show the modifications essential for winning the competition.

However, besides this, natural selection also plays important role because nature selects only those organisms which are fit to live and the rest perish.

Sustaining and selected organisms can perform reproduction and thereby give rise to the new species with their own specific characters. Darwin’s theory of natural selection was widely accepted for long duration.

Lamarckism

Jean-Baptiste Lamarck proposed that morphological changes occurring in living organisms are responsible for evolution and the reason behind those morphological changes is activities or laziness of that organism.

He called this concept as principle of ‘use or disuse of organs’.

He said that the neck of giraffe has become too long due to browsing on leaves of tall plants by extending their neck for several generations.

Shoulders of the ironsmith have become very strong due to frequent hammering movements.

Wings of birds like ostrich and emu have become weak due to no use.

Legs of the birds like swan and duck have become useful for swimming due to living in water and snakes have lost their legs by modifications in their body for burrowing habit.

All these examples are types of ‘acquired characters’ and are transferred from one to another generation.

This is called as theory of inheritance of acquired characters or Lamarckism.

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Human Evolution

Last dinosaurs disappeared approximately seven crore years ago. At that time, monkey-like animals are said to be evolved from some ancestors who were more or less similar to the modern lemurs.

Tail of these monkey-like animals of Africa is said to be disappeared about 4 crore years ago.

They developed due to enlargement in brain their hands were also improved and thus ape-like animals were evolved.

Meanwhile, these ape-like animals reached the South and North-East Asia and finally evolved into gibbon and orangutan.

Remaining ape-like animals stayed in Africa and from them, gorilla and chimpanzee evolved about 2.5 crore years ago.

Evolution of some of the 2 crore year old species of apes seems to be occurred in different way. They had to use their hands more for eating food and other work.

First record of human-like animal is with us in the form of ‘Ramapithecus’ ape from East Africa. Afterwards, this ape grown up in size and became more intelligent and thus the ape of South Africa evolved about 40 lakh years ago.

The morphology of these human-like animals started to appear like to be the member of the genus Homo, about 20 lakh years ago and thus skilled human developed.

About 15 lakh years ago, human walking with erect posture was evolved. It may have existed in China and Indonesia of Asian continent.

Evolution of upright man continued in the direction of developing its brain for the period of about 1 lakh years and meanwhile it discovered the fire.

Brain of 50 thousand year old man had been sufficiently evolved to the extent that it could be considered as member of the class- wise-man (Homo sapiens).

Neanderthal man can be considered as the first example of wise-man. The Cro-Magnon man evolved about 50 thousand years ago and afterwards, this evolution had been faster than the earlier.

About 10 thousand years ago, wise-man started to practice the agriculture. It started to rear the cattle-herds and established the cities.

Cultural development took place. Art of writing was invented about 5000 years ago and thus the history had been started.

Modern sciences emerged about 400 years ago and industrial society was established about 200 years ago and now we have reached at this stage, and still we are searching the details of roots of human ancestry.


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