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.

 SAVIOURS OF BIODIVERSITY

Environmental pollution is causing a lot of distress not only to humans but also to animals, driving many animal species to endangerment and even extinction. Methods are being devised to save this precious biodiversity.

GREEN CHEMISTRY

Green Chemistry is a specific type of prevention of pollution. It involves the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. It has been applied to a wide range of industrial and consumer goods, including paints, dyes, fertilizers, pesticides, plastics, medicines, electronics, dry cleaning, energy generation and water purification.

          Hazard is simply another property of a chemical substance. As properties of chemicals are because of their specific molecular structure, they can be modified by changing that structure. Various types of hazards that can be handled by Green Chemistry include physical hazards (being explosive or inflammable), toxicity (being carcinogenic or cancer causing, or lethal) or global hazards (climate change or stratospheric ozone depletion). Like a substance can be designed to have a low melting point or green colour, it can also be designed to be non-toxic.

Tools used in Green Chemistry

By choosing an alternate synthetic design, we focus not on the ultimate molecule but on the synthetic pathway used to create it. Modification of the synthesis can lead to the same final product, yet reduce or eliminate toxic starting materials, by-products and wastes. The following tools can be used to modify a synthesis:

1. Alternative Feedstocks (Starting Materials) The selection of a feedstock, i.e., the starting material used for the manufacture of a product, determines what hazards will be faced while handling this substance. A feedstock must be evaluated to determine whether it possesses chronic toxicity, carcinogenicity, ecotoxicity, etc. Currently, most of the organic chemicals are made from petroleum feedstocks. Petroleum undergoes oxidation during conversion to useful organic chemicals. This oxidation step is one of the most environmentally polluting steps of chemical synthesis. It has contributed to the risk to human health and the environment, mainly through the use of heavy metals, like chromium, as oxidising agents. It is, therefore, important to reduce the use of petroleum-based products. Agricultural and biological feedstocks are excellent alternative starting materials. They are already highly oxygenated. Therefore, their use eliminates the need for the polluting oxygenation step. A raw material or feedstock should be renewable rather than depleting. Petroleum and other fossil-fuel based feedstocks are depleting and feedstocks based on biomass and agricultural wastes are renewable. At present a host of agricultural products like soy, potatoes, corn and molasses are being transformed through a variety of processes into consumer products like textiles, nylon etc.

2. Alternative Reagents Alternative reagents are being increasingly used to carry out synthesis. For example, heavy metals, used in petroleum oxidation processes, are quite toxic and carcinogenic. They are being replaced by light to carry out the required transformation.

3. Alternative Solvents Many solvents commonly used in synthesis are volatile organic compounds (VOCs) that cause smog when released in air. Individuals with respiratory problems suffer great distress because of this environmental effect. Solvents like methylene chloride, chloroform, carbon tetrachloride, benzene, etc. have been identified as suspected human carcinogens. The uses of chlorofluorocarbons (CFCs) range from cleaning solvent, propellant, blowing agent for moulded plastic foams, to refrigeration. CFCs have very low direct toxicity to humans and wildlife, and are both nonflammable and non-explosive. However, CFCs are known culprits of ozone layer depletion. Some of the alternatives to these organic solvents include the use of supercritical or dense phase fluids, such as supercritical carbon dioxide. This system is not harmful from human health and environmental point of view.

            Supercritical fluids are obtained by subjecting small molecules, like carbon dioxide, to the appropriate temperature and pressure to attain the critical point at which the molecules possess the character of a fluid which is a cross between a liquid and a gas. The properties of this fluid (solvent) can be adjusted by adjusting the parameters of temperature and pressure. Supercritical solvent systems are now replacing a variety of other traditional organic solvents.

                Now methods are being developed where the reagents and feedstocks serve as the solvent as well. In some cases the reagents and feedstocks are made to react in the molten state to ensure proper mixing and optimal reaction conditions, or on solid surfaces such as specialised clays. Thus, ways are being designed to carry out reactions in solventless systems. If a solvent is essential for a particular synthesis, then the most innocuous one must be selected. Water is the safest solvent possible. A major problem with many solvents in relation to human health and the environment is their ability to volatilise. The use of immobilised solvents may serve as a solution. Immobilisation can be done by binding the solvent molecule to a solid support (polymer), so that it becomes non-volatile. Some polymers are beingdeveloped which have solvent properties and are not hazardous.

4. Alternative Product (Target Molecule) While designing safer chemicals (target molecules), the object is to maximise the functional benefits of a molecule and minimise or eliminate its toxicity or other hazards. This is done by identifying the part or parts of the molecule that produce toxic effects, and also those that are responsible for its desired function. The part related to the toxic effect can be avoided or suitably changed to reduce or eliminate the toxic effect.

        Another way to reduce hazardous effects of a substance is to minimize its bioavailability. If a toxic substance is not able to reach its target organ (e.g. heart, lungs, liver), where it can manifest its toxicity, then it is rendered innocuous for all purposes. By changing the physical and chemical properties of a molecule, like solubility in water and polarity, the absorption of molecules through biological membranes and tissues can be made difficult or impossible. Elimination of absorption and bioavailability leads to reduction in toxicity.

5. Green Analytical Chemistry The detection, measurement and monitoring of chemicals in the environment is done through Analytical Chemistry. Instead of determining environmental problems after they occur, Green Chemistry seeks to prevent the formation of toxic substances. Even minute amounts of toxic substances are detected with the help of sensors and process controls are adjusted to minimise or stop its formation.

6. Alternative Catalysts Catalysis has increased the level of efficiency of chemical synthesis, and has also brought about environmental benefits. Use of new catalysts has eliminated the need for large quantities of reagents that would have been otherwise required to carry out those syntheses. Such large amounts of regents would have increased the bulk of the waste stream.

7. Minimal Energy Requirements Energy requirements of a synthetic procedure should be minimised because energy generation and consumption bring about a major environmental effect. The advantage of using a catalyst is that it lowers the energy of activation needed to accomplish a reaction, and therefore, minimises the thermal energy required for the transformation.

        Microwave energy is now being utilised in order to effect chemical reactions rapidly, and generally in the solid state. This eliminates prolonged heating necessary to carry out a reaction. Through the use of ultrasonic energy, the conditions of the reactants are considerably changed to promote a chemical transformation.

8. Alternative Methodology Unnecessary use of blocking groups, protecting groups, additional functional groups should be avoided, because this requires use of materials (often hazardous) to make the substance and generates a waste in the regeneration of the original substance.

        Some methods make use of toxic chemicals such as cyanide or chlorine. In addition, these methods at times generate large quantities of hazardous wastes. For example, the pulp and paper industry uses chlorine compounds in processes that generate toxic chlorinated organic waste. Green chemists have developed a new technology that converts wood pulp into paper using oxygen, water, and polyoxometalate salts. Water and carbon dioxide are the only by-products. Substances used in a chemical process should be chosen so as to minimise the chances of chemical accidents, including explosions and fires.

9. Designing for Biodegradability Chemical products should be designed so that after their function is over they do not persist in the environment and do not accumulate in plant or animal systems, but break down into innocuous degradation products. Plastics are known for their durability and long life. That is why they cause environmental concerns in oceans and other aquatic media. Pesticides tend to bioaccumulate in many plant and animal species, thereby causing damage to the species itself, or, to humans if consumed. These products should be designed so that they do not remain in their initial state in the environment after their useful life is over. Their degradation products also should not be toxic or hazardous.

10. Green Chemistry Evaluation Whether dealing with a reagent, solvent, product, starting material or the process itself, the following essential characteristics need to be known to conduct a Green Chemistry evaluation:

(i) Toxicity to humans

(ii) Toxicity to wildlife

(iii) Effects on the local environment

(iv) Global environmental effects