Method of biological classification
Merriam-Webster defineschemotaxonomy as the method ofbiological classification based on similarities and dissimilarity in the structure of certaincompounds among theorganisms being classified. Advocates argue that, asproteins are more closely controlled bygenes and less subjected tonatural selection than theanatomical features, they are more reliable indicators ofgenetic relationships. The compounds studied most are proteins,amino acids,nucleic acids,peptides etc.
Physiology is the study of working oforgans in aliving being. Since working of the organs involveschemicals of thebody, these compounds are calledbiochemical evidences. The study ofmorphological change has shown that there are changes in thestructure of animals which result inevolution. When changes take place in the structure of aliving organism, they will naturally be accompanied by changes in thephysiological orbiochemical processes.
John Griffith Vaughan andVictor Plouvier were among the pioneers of chemotaxonomy.
Biochemical products
[edit]Thebody of anyanimal in the animal kingdom is made up of a number ofchemicals. Of these, only a few biochemical products have been taken into consideration to deriveevidence for evolution.
- Protoplasm: Every livingcell, from abacterium to anelephant, fromgrasses to theblue whale, has protoplasm. Though the complexity and constituents of the protoplasm increases from lower to higher living organism, the basic compound is always the protoplasm. Evolutionary significance: From this evidence, it is clear that all living things have a common origin point or acommon ancestor, which in turn had protoplasm. Itscomplexity increased due to changes in the mode of life andhabitat.
- Nucleic acids:DNA andRNA are the two types of nucleic acids present in all living organisms. They are present in thechromosomes. The structure of these acids has been found to be similar in all animals. DNA always has two chains forming adouble helix, and each chain is made up ofnucleotides. Each nucleotide has apentosesugar, aphosphate group, andnitrogenous bases likeadenine,guanine,cytosine, andthymine. RNA containsuracil instead of thymine. It has been proved in thelaboratory that a single strand of DNA of onespecies can match with the otherstrand from another species. If thealleles of the strands of any two species are close, then it can be concluded that these two species are more closely related.
- Digestive enzymes arechemical compounds that help indigestion. Proteins are always digested by a particular type of enzymes likepepsin,trypsin, etc., in all animals from a single celledamoeba to ahuman being. The complexity in the composition of these enzymes increases from lower to higher organisms but are fundamentally the same. Likewise,carbohydrates are always digested byamylase, andfats bylipase.
- End products of digestion: Irrespective of the type ofanimal, the end products of protein, carbohydrates and fats areamino acids,simple sugars, andfatty acids respectively. It can thus be comfortably concluded that the similarity of the end products is due tocommon ancestry.
- Hormones aresecretions fromductless glands called theendocrine glands like thethyroid,pituitary,adrenal, etc. Their chemical nature is the same in all animals. For example,thyroxine is secreted from the thyroid gland, irrespective of what the animal is. It is used to controlmetabolism in all animals. If a human being is deficient in thyroxine, it is not mandatory that this hormone should be supplemented from another human being. It can be extracted from anymammal andinjected into humans for normal metabolism to take place. Likewise,insulin is secreted from thepancreas.
If the thyroid gland from atadpole is removed and replaced with abovine thyroid gland, normal metabolism will take place and the tadpole willmetamorphose into afrog. As there is a fundamental relationship among these animals, such exchange of hormones orglands is possible. - Nitrogenous Excretory Products: Mainly three types of nitrogenous waste is excreted by living organisms; ammonia is a characteristics of aquatic life form, urea is formed by the land and water dwellers, uric acid is excreted by terrestrial life forms. A frog, in its tadpole stage excretes ammonia just like a fish. When it turns into an adult frog and moves to land, it excretes urea instead of ammonia. Thus an aquatic ancestry toland animal is established.
Achick on up to its fifth day of developmentexcretesammonia; from its 5th to 9th day,urea; and thereafter,uric acid. Based on these findings, Baldwin sought a biochemical recapitulation in the development ofvertebrates with reference tonitrogenous excretory products. - Phosphagens areenergy reservoirs of animals. They are present in themuscles. They supplyenergy for thesynthesis ofATP. Generally, there are two types of phosphagens in animals,phosphoarginine (PA) ininvertebrates andphosphocreatine (PC) in vertebrates. Among theechinoderms andprochordates, some have PA and others PC. Only a few have both PA and PC. Biochemically, these two groups are related. This is the most basic proof that the firstchordate animals should have been derived only from echinoderm-likeancestors.
- Body fluid of animals: When the body fluids of bothaquatic andterrestrial animals are analyzed, it shows that they resemblesea water in theirionic composition. There is ample evidence that primitive members of most of thephyla lived in thesea inPaleozoic times. It is clear that the first life appeared only in the sea and then evolved onto land. A further point of interest is that the body fluids of most animals contain lessmagnesium and morepotassium than thewater of the present-dayocean. In the past, the ocean contained less magnesium and more potassium. Animals' bodies accumulated more of theseminerals due to the structure of DNA, and this characteristic remains so today. When the firstlife forms appeared in the sea, they acquired the composition of the contemporary sea water, and retained it even after their evolution onto land, as it was a favorable trait.
- Opsins: In the vertebrates,vision is controlled by two very distinct types of opsins,porphyropsin andrhodopsin. They are present in therods of theretina.Fresh water fishes have porphyropsin;marine ones and land vertebrates have rhodopsin. Inamphibians, a tadpole living in fresh water has porphyropsin, and the adult frog, which lives on land most of the time, has rhodopsin. Incatadromous fish, which migrate from fresh water to the sea, the porphyropsin is replaced by rhodopsin. In ananadromous fish, which migrates from the sea to freshwater, the rhodopsin is replaced by porphyropsin. These examples show the freshwater origin of vertebrates. They then deviated into twolines, one leading to marine life and the other to terrestrial life.
- Serological evidence: In recent years,[when?] experiments made in the composition ofblood offer good evidence for evolution. It has been found that blood can betransmitted only between animals that are closely related. The degree of relationship between these animals is determined by what is known as theserological evidence. There are various methods of doing so; the method employed byGeorge Nuttall is called theprecipitation method. In this method,anti-serum of the involved animals has to be prepared. For human study,human blood is collected and allowed toclot. Then, theserum is separated from theerythrocytes. Arabbit is then injected with a small amount of serum at regular intervals, which is allowed toincubate for a few days. This formsantibodies in the rabbit's body. The rabbit's blood is thendrawn and clotted. The serum separated from thered blood cells is called the anti-human serum.
When such a serum is treated with that of blood ofmonkeys orapes, a clear whiteprecipitate is formed. When the serum is treated with the blood of any other animal likedogs,cats, orcows, no precipitate appears. It can thus be concluded that humans are more closely related to monkeys and apes. As a result, it has been determined thatlizards are closely related tosnakes,horses todonkeys, dogs to cats, etc. This systematic position ofLimulus was controversial for a long time, but has been found to show that human serum is more closely related toarachnids than tocrustaceans.
The field of biochemistry has greatly developed sinceDarwin's time, and thisserological study is one of the most recent pieces of evidence of evolution. A number of biochemical products like nucleic acids, enzymes, hormones and phosphagens clearly show the relationship of all life forms. The composition of body fluid has shown that the first life originated in the oceans. The presence of nitrogenous waste products reveal the aquatic ancestry of vertebrates, and the nature of visual pigments points out the fresh water ancestry of land vertebrates. Serological tests indicate relationships within these animal phyla.
When only fragments of fossils, or somebiomarkers remain in a rock or oil deposit, the class of organisms that produced it can often be determined usingFourier transform infrared spectroscopy[1]
- ^Chen, Y., Zou, C., Mastalerz, M., Hu, S., Gasaway, C., & Tao, X. (2015). Applications of Micro-Fourier Transform Infrared Spectroscopy (FTIR) in the Geological Sciences—A Review. International Journal of Molecular Sciences,16(12), 30223-30250.
