mi(sual).com

– © Chiangrenga

“How great is the onward rush of science”, Darwin to Alfred Russel Wallace(1872). Once we Homo sapiens look out over a world of nature, we never asked what to come, where it ends and how its start. A Pigeon was a Pigeon because it was made to be, there were some essential nature- an essence- that made it that way. The world didn’t change, it didn’t sit still either. But Old things die and new things were born.

Biological evolution, simply put, is descent with modification. This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history and diversity of life. It is the basic framework to understanding all biological disciplines – from molecular biology, physiolgy, biochemistry, genetics to ecology.

Thus evolution is the only unifying theme of all branches of life sciences, as Theodosius Dobzhansky remarked, “Nothing in biology makes sense except in the light of evolution. The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother.

Man has always been perplexed about the Origin of life on Earth.Evolutionary theory has affected Biology like no other single theory. It has impressed scientists with the fundamental unity of all of biology. For a decades , number of theories and hypothesis have been suggested to explain the origin of life in their own way. In addition to the distinctions between different areas of evolutionary theory, scientists also find it helpful to distinguish amounts of biological change or evolution.

By the middle of the 19th century, the theory of biogenesis had accumulated so much evidential support, due to the work of Louis Pasteur and others, that the alternative theory of spontaneous generation had been effectively disproven. Pasteur himself remarked, after a definitive finding in 1864, “Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.The collapse of spontaneous generation, however, left a vacuum of scientific thought on the question of how life had first arisen.

In a letter written by Darwin in 1871 to his friend Sir Joseph Hooker – a great Botanist he stated, “………….. But if we could conceive of some warm little pond, with all sorts of ammonia and phosphorus salts, light, heat, electricity etc..present , that a protein compound was chemically formed ready to undergo still more complex changes, at present day such matter would be instantly devoured or absorbed which could not have been the case before living creatures were formed .”

There were evolutionary ideas before Darwin, but his writings presented the first systematic theory along with extensive supporting evidence.The great naturalist appeared in the ripeness of time, when the world was ready for his splendid generalizations. Serving as naturalist on the HMS Beagle during a five-year voyage around the world, Darwin had observed many small variations between similar species. Six years later, reading Malthus’s essay on human populations competing for limited resources, he found the clue for a theory by which to interpret the data collected on the voyage. Two ideas were central in his theory of evolution.

First, in every population there are small random variations, which can be inherited. Second, in the struggle for survival some of these variations confer a slight competitive advantage, leading over a period of many generations to the natural selection of the characteristics that contributed to survival. Darwin argued that through such natural selection new species have come into existence. “The theory of natural selection” of his was at first greatly misunderstood. Thus some writers thought it implied conscious choice in the animals themselves, others that it was the personification of some active power. By many it was thought to be practically the same idea as Lamarck’s. Herbert Spencer’s alternative phrase, “ the survival of the fittest,” probably helped to spread a clear appreciation of Darwin’s meaning. In The Descent of Man (1871) he extended his theory to include human origins.

It is assumed that simple one-celled Organism that resemble Cyanobacteria of today found existence about 3600 million years ago and that the first organism evolve on Earth must have been able to live without oxygen.Fossils of  both primitive single celled and more advanced multicellular organisms begin to appear in abundance in rocks from this era. At this time biological diversity increased greatly to become eukaryote cells. Different to the prokaryotic cells, the eukaryotic cells are larger and have a complex internal organisation and which includes a nucleus housing the DNA on the chromosomes and specialised structures known as organelles.

The oldest fossil evidence of multi-cellular animals, or metazoans, are burrows which suggest they were made by smooth, worm-like creatures. These fossils have been found in rocks in various places including China, Canada, India. The imprints of these soft bodied animals reveal little else but their basic shape. Oxygen must have been freely available by the time the first eukaryotic cells arrived, released through the proliferation of cyanobacteria, earlier in the Precambrian.

As is paramount to known that the first organism were heterotrophs. They were anaerobic, as oxygen was not found on earth. They utilise the compound present in Oceans. Later with the evolution of known photosynthetic organisms came into existence in addition to the existence of chlorophyll molecule Oxygen was realise as a by product of photosynthesis and this changed the earth’s  atmosphere from reducing to oxidising one. It was also the end of ‘abiosynthesis’.

The chemical evoluiton was followed by the biological evolution. Thus, Genesis 1:11 says, ‘Let the Earth bring forth greenness’(deshe = green matter, refering to chloroplast to put oxygen into the air – Indispensable that algae being the first ).

With the rise of O2-producers, the earth’s atmosphere became progressively richer in O2 – a powerful oxidant and deadly poison to anaerobes adapted to a milder environment. Responding to the evolutionary pressure of the so-called ‘oxygen holocaust’, some lineages of microorganisms gave rise to aerobes that obtained energy by passing electrons from fuel molecules to O2. Because of this aerobic organisms had an energetic advantage in the growing O2-rich environment, which resulted into the predominance of aerobic organisms.

Evidence from Biogeography in favour of Evolution-

Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature? With this in views The theory of natural selection of Darwin began in 1831 when he joined the expedition of the British Admiralty for navigational mapping and boarded the ship H.M.S Beagle.Darwin argued that if so much change can be achieve by artificial selection in a short period of time, then natural selection should be considerable modification of species over hundred and thousand of generations.

He postulated that Natural selection operating in a varying conditions over a vast span of time could account for entire diversity of life. During his voyage , Darwin observe and studied a wide variety of plants and animals on continents and Islands and in distant sea. He found giant tortoises with weights over 500 lbs (250 kg) and shells measuring 59 inches (150 cm) , meter-long marine and land iguanas, many unusual plants, insects, lizard and sea-shells, on Galapagos Island about 900 kilometer of the west coast of South America.(A relatively large tortoise, related to the Galapagos tortoise so called in  April 7,2010 Cerrejonemys wayuunaiki lives on the South American mainland )The Galapagos Island has twenty two different Islands only few mile apart. He observe that the Galapagos Island have many endemic species of plants and animals.

To his suprise, he found a group of small black birds who were originally seed-eaters and have become insect eaters , present in the Island. These are called Darwin’s finches.As man can produce and certainly has produced a great result by his methodical and unconscious means of selection, what may not nature effect? He observe that different different geographical localities have similar habitat but house different species. According to Darwin’s hypothesis, the descendant populations from ancestral group, could radiate into ather areas, where the new environment conditions brought about the suitable adaptation by evolution. Living in Isolation for long  period of time new kinds of Finches emerged that could function and survive in the new habitats. Such an evolutionary process may be termed as adaptative radiation.Wallace pushed the study of biogeography to graunder scales than Darwin.

Evolution of man

Human evolution can be best understood from molecular analyses particularly those of the genome sequences. Like all other organisms, humans have evolved over time from earlier species, and share a molecular and genetic relationship to all other forms of life on Earth. The study of human evolution involves understanding the similarities and differences between humans and other species in their genes, body form, physiology, and behavior.

From the genomes of various living primates – different apes such as gorilla, chimpanzee, orangutan – there is clear evidence that we all share common ancestry and that the human line seperated out from these apes about 6 mya. The origin of humans was accompanied by the emergence of new behavioral and cognitive functions, including language and specialized forms of abstract representation. Complete sequence of our genome and the presently on going sequencing of Chimpanzee genome will defnitely provide more solid understanding of our relationship and the level of evolution we have gone through.

However, molecular studies alone can not give a complete evolutionary scale of human because we Homo sapiens are fortunately and unfortunately the only survivor of human kind. Thus much of the knowledge we have are from the traces of extinct humans and paleoanthropology is the most direct evidence that could provide the sequential picture evolutionary changes at different time lines, and thus our human ancestors.Evolution not only explains why animals appear and function asthey do, but it also explains family relationships within the animal kingdom.

Similar Posts:

• Darwin sel tehsek suh u!
• The Vatican says evolution theory is compatible with the Bible
• Zopa Evolution theory….
• Charles Darwin A Piangthar An Ti Maw!?
• Never Give up!!

Recent Posts:

• NANG NEN NGEI HIAN
• June 2017, Mizo(ram) diary
• MIZORAM POLITICS A PARTY TE INCHIRHTHEHNA TAWP THEI LO: KAWNG CHHIA “MNF hovin anmahni mawng an hlim”
• Dawihzep
• CALL GIRL AN TI!

This entry was posted on Wednesday, April 21st, 2010 at 8:14 am and is filed under Education. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.