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Evolution

posted Jul 31, 2015, 4:59 PM by Upali Salpadoru   [ updated Jul 10, 2016, 10:59 PM ]

Fig.1 From Ape to Man.





Almost all biologists agree that all forms of life have been descended from a common ancestor. According to this we are not only related to Apes and monkeys but also to cabbage and onion.  

In order to proliferate life with such a fantastic number of variations as it has happened there has to be a wonderful mechanism. That is EVOLUTION.

 

There is no way to doubt this as the scientists can provide sufficient evidence to prove this. The Geologists produce fossil records of different eras, and the micro biologists have DNA proof of relationships. The process has to be something unique.

Fig.2. Tree of Evolution.

What sort of changes caused evolution?
 


Survival of the fittest”  and “ Natural selection” were the factors stressed by Charles Darwin and Alfred Wallace. 

Prior to selection there has to be off springs even with a minute difference to the parent. If all the young ones are identical copies of the original there cannot be any selection.

Fig.3.
Johann Mendel Austrian- 1822 to884


Men
del recognised that there was a ' unit' that carry the characteristics of parent to off spring. As this is the beginning of genetics, Mendel is considered as the Father of 'Genetics.'

These could only be properly explained only after the ‘gene’ was discovered in the 20th century.


Consider some animals of a specie Living in two different places, 

A and B. If there is more food at A the animals there will grow bigger and better while those at B will retard. 

This is not evolution as the changes are not hereditary.

If the retarded animals get more food they can revive. Changes in evolution are of a permanent nature.


Read about Charles Darwin


Alfred Russel Wallace.jpg

Althogh Darwin had his theory formulated around 1830, he kept it to himself for 20 years.. Only when Russel Wallace sent his theory of evolution to Darwin, he developed sufficient confidence to forward it giving him the due credit.


Evolution is due to genetic variations. 

This may occur basically in three different ways.

1.Mutation, 2.Genetic drift, 3.Sexual reproduction.



Mutations

These are due to changes that occur due to changes in chromosomes. 

During meiosis (Reduction division) Chromosomes that go to form gametes (Reproductive cells) are replicated. 

If an error creeps in during this process, the off spring produced will not be identical to the parent.

Gene flow

When individuals from one population migrates into another population of the same specie gene exchange can take place. This can result in slightly different off springs.


Sexual reproduction.

Sex can introduce variations in gene combinations into a population. This is genetic shuffling.


Natural selection

Once the new varieties have been formed the environment will be more healthy for certain individuals

Ev 2.jpg

The bird here is more likely to pick those having the contrasting colour green. The brown beetles have a better chance of survival and the greens will diminish or may even become extinct.


Fig. 4 Natural selection.

History of Evolution.



Sir Fred Hoyle
 and Prof. Chandra Wickremasinghe states in a book, “the Evolution by Natural Selection,  is as unlikely as  a tornado sweeping through a junkyard spontaneously assembling a Boeing 747 airplane”.  Their favoured theory was ‘Panspermia’, that the living spores would have come from outer  space. Hindus, Christians and Muslims had other views scrolled in their ancient texts. Buddhists, following the philosophy , “Thy hand is to thine own head”  do not recognize a creator..

One of the first to forward a theory of evolution, based on observations rather than dogmas, was the Frenchman, Chevalier de Lamarck (1744 – 1829). He assumed that there is a force changing simple animals into more complex forms to suit the environmental changes. In the 19th Century Charles Charles Darwin, who made a detailed study of all life forms in many countries around the globe introduced  the theory that species undergo changes over very long periods of time. His conclusions were so revolutionary that he kept them to himself for 15 long years.  By this time  another keen naturalist who had systematically studied living specimens, in the Amazon basin and in the Far East, passed his views on the subject to Darwin.   The latter finding the views of both biologists to be identical, published them as a joint paper in 18.   


No other literary work has ever been received with so much criticism as well as acclaim as the Darwin’s book, ‘On the origin of species’ published in 18   In an aristocratic society where the intelligentsia had been descended from Lords and Earls and were really proud of their ancestry it  as a humiliating shock to hear that the man has been evolved from an Ape. It has been reported that all copies of the book were sold out on the same day they were released. T H Huxley who subsequently fought tooth and nail in support of Darwin, on the first reading of it has wondered . “How extremely stupid not to have thought of that” with reference to the theory of natural selection. 

The ‘theory of biological evolution’ had two aspects; observed facts and an interpretation. Man had learned to breed plants and animals according to his needs.The cultivated varieties of plants produced a better and a higher yield than the wild varieties. Similarly the domesticated animals, such as pigeons and dogs,  showed much more variety than in the wild. These are observed facts. Now what is the interpretation? In the case of cultivated plants and domesticated animals it is a case of selective breeding which may be termed as ‘artificial selection’. Consider the poultry farming; Hens are birds, but they hardly fly. A farmer did not want fast flying hens, he selected the eggs from the best layers for hatching. After several hundred years the streamlined jungle fowls became chubby, docile and better layers.


Charles Darwin pointed out that a similar process takes place in the wild too. He called this ‘Natural selection’. Consider a pack of spotted dear; leopards hunt them for their food. The slow ones generally become prey while the faster runners escape. So only the faster ones will be able to reproduce and pass on their genes. If such minor changes go on for millions of years, the ultimate specimens would be completely different from the original stock. Such changes that can initiate a new specie are called macro-evolution while minute changes go as micro-evolution. 

 In Uganda 100years ago all male elephants had tusks . Now only a few posess tusks. Those with the long tusks have mostly shot down before they were able to pass their genes. So in the present population those genes that contributed to long tusks have become scarce. This is natural selection that has become evident in modern times.

Although Charles Darwin had to contemplate about evolution almost blindly in the 19th Century, with the advancement of molecular biology how the changes occur can be clearly explained. All traits, such as the size, mode of nutrition are all chemically programmed in the genes of an individual. The genes are present in a stable molecule called the DNA. When the cells divide for binary fission, growth or to form gametes for sexual reproduction , the DNA strand opens up exposing the genes. This  is the time they can get damaged by various irritations. Sometimes it could be some kind of changing of  places. These are   known as mutations. Most of the mutations are not beneficial to the individual.For example a mutation  may occur in the tissues of the skin of a man. These cannot be passed on to the children. In higher animals, only the mutations in the reproductive cells could become hereditary.Imagine a section of the population migrates into one kind of a habitat such as a rocky rough terrain, and the other into a marshy area. If  you think they get adapted wilfully to overcome the harshness of the environment it is not correct. What really happens is ones that have genes best suited for the habitat will survive and reproduce while the misfits will perish. After millions of years one specie can similarly branch of to many different species. This is known as ‘speciation’.

Natural selection is not the only way a population can change over time. ‘Sexual selection’ is 
another mode of operation in the wild. Consider fan tail of the peacock; it is very conspicuous and 
a predator finds it easy to spot it while performing the nuptial dance as the sunrises over a plane. 
One that has the most attractive plumage must be getting the most number of mates. As there is a 
better chance of their genes passing over to the progeny as time goes they become more and more attractive.


Fig.2.  This plumage has been developed due to sexual selection.

Most creationists believe that species can undergo changes. If not they ask, “how can there be so 
many types of human beings, when only Adam and Eve had been created?”.  But they refuse to believe any new living forms can be formed as a result of evolution.

Just as Fred Hoyle, they have many questions which are not easy to counteract. For example they want to know, how such a specialised organ as the eye could have evolved just by chance selections? If for example, it is the chimp that evolved to become the man they wish to know why intermediate stages have not been found in the fossil records. They also cast doubts about the isotope dating of the rocks and fossils.

A true scientific  theory should be falsifiable. Can the theory of evolution be proved to be wrong?

The author himself has shown the way "If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous successive slight modifications my theory would absolutely break down”


The eminent British / Indian  biologist Prof. JBS Haldane has shown anotherc way;

"If anybody can show that a mammal has been  stratified in the carboniferous rocks,. that will be the last nail on the coffin of The of the theory of evolution."

 

Age / million yrs.

Period

Forms of Life

Remarks

4600 to 3800

Formation

 of Earth

No Life forms

 

3800 to 2500

Archaean

Life appears.

Stromalites (photosynthetic Bacteria)

Methane and ammonia depleting building up Oxygen

2500 to  600

Proterozoic

Bacteria, archaeans,

Procaryota

Continents appeared

600 to 540

Vendian

Sponges, multi-celled animals appear

Super continent Rodinia.

540 to 500

Cambrian

First shellfish, primitive fish, trilobites, corals, mollusks.

Explosion of life forms

505 to 438

Ordovician

First land plants, corals, Nautiloids

 

Ends in mass extinction

438 to 408 

Silurian.

First insects, vascular plants on land

 

408 to 360 

Devonian.

Amphibians, sharks, bony fish, ammonoids, and spiders. Many fish

 

360 to 280

Carboniferous 

Widespread coal swamps. First reptiles, winged insects.

 

280 to 245 

Permian.

Reptiles. Amphibians abundant.

Pangaea forms Ends with mass extinction.

245 to 208

Triassic

Mammals, dinosaurs, frogs, turtles, crocodyloformes

 

208 to 146

Jurassic

Abundant dinosaurs, first birds.

 

146 to 65

Cretaceous

First flowering plants, snakes, crocodilians.

Mass extinction,  kills dinosaurs,

65-24

Paleogene

Deer, cats, pigs, tapirs, and rhinos, elephants, horses, owls, shrews, hedgehogs, and rabbits evolve.

 

24-1.8

Neogene

Australopithecus. Sheep, cattle, whales, bears, mice, rats, apes, monkeys, dogs,  birds .

 

1.8 -today

Quarternary

Humans, mammoths, mastodons, saber-toothed cats.

 

 

REFERENCE

 1.   Evolution for dummies  by Greg Krokonis and Tracy Barr
2.   Darwin's Black box by Michael J Behe.
3.   Climbing mount improbable by Richard Dawkins
4.   Darwin's Ghost by Steve Jones.



  Bio U test.jpg

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