EVIDENCES OF EVOLUTION

        The word “evolution” is derived from the Latin word “evolvere” which means to “unroll” or “unfold”. Thus, the theory of Organic Evolution states that it’s a kind of gradual unfolding or formation of more complex, advanced and present day forms from simple and primitive organisms living in the past,millions of years ago. 

There are various evidences available to prove this point. viz.

(a) Morphological and Anatomical Evidences

(b) Embryological evidences

(c) Paleontological (Fossils) evidences: The study of fossils (paleontology) is the best and most direct conventional type of evidence, e.g., the fossil of Archaeopteryx*. (“Archaeo” means primitive and “ptera” means wings in Latin) is a classical example of evolution of birds from reptiles, because it contains features of both the forms. Similarly, the world famous fossil of “Lucy” (Australopithecus afarensis) shows that “bipedal” locomotion arose for the first time in ancestral man here and finally led to the development of erect “modern” man.

(d) Biogeographical evidences

(e) Biochemical evidences: The most convincing evidence of common ancestry comes from similarities of certain biomolecules viz. composition of protoplasm, enzymes, cytochrome ‘C’ (respiratory pigment present in all eukaryotic cells), blood serum proteins, hemoglobin, insulin, etc. The degree of molecular homology is more in closely related forms and vice versa, e.g.,amino acid sequence for cytochrome ‘C’ of humans and chimpanzee is identical.

(f) Genetic evidences or Molecular evidences: These are the latest observable tools in determining the phylogenetic relationships between organisms and allow molecular comparisons even between very uncommon relatives with no morphological, behavioural, physiological or ecological relationships e.g., bacteria and humans. Some of the molecular tools used to prove evolutionary relationships are:

•         Amino acid analysis or sequencing e.g., Hb, Mb sequencing in para and orthologous species.
•         Nucleotide sequence analysis (data from 5S ribosomal RNA)
•         DNA hybridisation
•         Restriction enzymes: which cleave DNA into fragments at particular sites like ECORI from                          E. coli. They allow comparisons among DNA of different species                                           
•         RFLPs (Restriction Fragment Length Polymorphisms) 

•         Mitochondrial DNA and microsatellites, etc.

 EVOLUTION OF LIFE

        The  theories explained how life must have originated on early primitive earth about 3.5 billion years ago, but it did not give any information about how the biological diversity arose. Again, there were different views about how this must have happened.

    Some of the dominant thoughts were: (i) Greek Theories (ii) Pre-modern Theories and (iii) Modern Theories. 

Among the Modern Theories, the following two are most popular. 

Theory of Inheritance of Acquired Characteristics

This theory was proposed by famous French naturalist Jean Baptiste Lamarck. It propounded that the characters were acquired by the organisms due to an “inner need” or “desire” of the organism and these acquired characters were then inherited. This theory was subsequently rejected.

Theory of Natural Selection

Charles Darwin, who is better known as the “Father of Evolution” was the architect of this world famous theory, which charmed both the scientists as well as laymen. This theory took shape when Darwin was aboard H.M.S. Beagle, the famous ship, for a voyage planned for world exploration.According to him, the struggle for existence, due to limited availability of resources, led to the survival of the fittest or natural selection

 ORIGIN OF LIFE

We salute the spirit of inquisitiveness of man, which gave birth to the discipline of science. The same spirit of questioning also led man to often wonder how life or the first organism came into existence. This quest led him to find answers to how, when and where life originated.

        For centuries, it was believed that life originated de novo. In addition several other scientific and non-scientific theories were also put forward.

Some of them are:

(i) Theory of special creation: (or Biblical Theory) – It was put forward by Father Suarez, a

Spanish Monk.

(ii) Theory of spontaneous generation (or Abiogenesis): (Gr, ‘a’ – absence, “bios” – life,

“genesis” – origin) or origin from non-living matter.

(iii) Theory of Panspermia or Cosmozoic Theory: According to this theory, life came from some

other planet. It’s still believed to be true by some scientists like Wikramsinghe, Francis Crick

and Leslie Orgel.

(iv) Biogenesis: Francesco Redi and Louis Pasteur laid the foundation for the Theory of

Biogenesis, which propounded that living organisms arise from pre-existing ones and not from

non-living matter.

(v) Chemosynthetic Theory or Chemogeny: This theory proposed that first form of life originated

from inorganic chemical elements by formative action of some external physical force viz.

lightening or cosmic rays, etc. It was put forward by A.I. Oparin and J.B.S. Haldane and the

experimental evidence was provided by Stanley Millar & Harold Urey. For example, Mighi

meteorite in Ukraine and analysis of another meteorite content viz. Murchison, Victoria in

Australia by space biologists also revealed similar composition indicating that similar processes

are still occurring elsewhere in space. However, in this case, although the presence of amino

acids and polynucleotide are similar to DNA, these are of chemical origin and therefore have

identical strands instead of complementary strands.

Tissues and Types of Tissues in Human Body

Tissues