Evolution throughout the Earth's history
Evolution is the way in which an organism changes over many generations,resulting in a species that is very much different from its early ancestors.
Most scientists believe that the first simple organism appeared on earth over 3,000 million years ago and as time progressed all plants and animals have arisen by a slow gradual change. This process which is constantly happening from one generation to the next, is known as evolution. Species with qualities that help them adapt to harsh environments live on while others become extinct.
History and origin of theories of Evolution
The idea of evolution was brought forth some 2500-3000 years ago. The Greeks were the first to propose the theory of evolution mostly influenced by the stories and legends of their Gods.
However, the first convincing theory of how evolution works was put forth in the middle of the 19th century by an English Naturalist Charles Robert Darwin (1809-1882). After travelling to the Galapagos Island located in the Pacific Ocean in the year 1831 in his HMS Beagle and studying the animals and birds of that island, he proposed the "theory of the survival of the fittest". He saw that plants and animals produce lots of offspring but that only a small number survive. He concluded that only the individual with the most useful features can survive in what he called the struggle for existence.
The example he put forward were the beaks of finches living on the island. Though they were the same species, they had different beaks to suit their food needs like a long beak for eating insects and hook like beak for cracking nuts . All these were influenced by the environment these birds were in . Therefore with this brought up the "theory of Natural selection".
Another theory was put forward by a French Biologist Jean Baptiste Lamarck (1744-1829) who believed mistakenly that animals evolved during their own lifetimes like for example Giraffes. They evolved by stretching and elongating their necks probably to get hold of leaves hanging high up on the trees.
Survival of the fittest
Individuals that are not well suited to their surroundings die out, leaving only the fittest ones to breed and pass the useful characters onto their offspring. This is called the " survival of the fittest". It explains the great variety of plant and animal life throughout the world, because the conditions vary from place to place, so animals adapt to fit.
The beginning of time
The reading of the oldest meteorite found on Earth is around 4.45 billion years old. Therefore scientists estimate the age of the Earth to be around that time. All life forms probably started from a single celled sea organism. From there on, evolution branched out in different directions. A group of fishes evolved into amphibians and gave rise to reptiles.
Archaeopteryx, which is said to have both avian and reptilian features lived around 150 million years ago. It had the wings and feathers of a bird and teeth of reptiles indicating an evolutionary stage between the two.
The most famous example of evolution is the evolution of the modern day horse from the size of a dog some 55-40 million years ago.
Evolution of horse
Step by step
With each new generation, the struggle for existence continues, with the result that plants and animals gradually change and become better adapted to their surroundings. These changes may almost be invisible but it takes place over millions of years and it makes a big difference.
Theory of natural selection
Conditions are not the same everywhere, so an advantageous variation in one region may be less useful in another. Species spread out may evolve or change over a long time into different species. Since this is a natural process where the less efficient individuals are wiped out and the fittest ones take its place, Darwin gave it the theory of natural selection.
Fossils in Sedimentary rock layers
Fossilized evidence in rocks
Fossilized rocks formed from layers of sand and mud on ancient sea beds have been found containing remains of plants and animals. Each layer of sedimentary rock showed organisms slightly different from the ones below suggesting changes over time.
Fossilized Amber rock
A common Ancestor
The bone structure of living beings also gives certain clues to evolution. A human arm,a bird's wings and a whale's flipper all look quite different and have different uses. But when looked more closely, their bone structures are very similar. This often suggests that these beings all evolved from a common ancestor. Since these creatures are in different environments, their hands got adapted to doing different jobs.
Structure of hand through evolution
The evolution of humans
Theory of Evolution in Man
Evolution process has also led to the evolution of modern age man. The modern theory in the evolution of man derives the belief that both man and ape has an ape-like ancestor that lived millions of years ago.
The different stages in the evolution of Man include:
1) Ramapithecus- This creature lived about 14 - 8 million years ago
2) Australopithecus ramidus- 4.4 million years ago
3) Australopithecus afarensis- 4 -2.8 million years ago
4) Australopithecus africanus- 3 - 2 million years ago
5) Australopithecus robustus- 2 -1.5 million years ago
6) Australopithecus boisei- 1.8 million years ago
7) Homo habilis- 2- 1.5 million years ago
8) Homo erectus- 1.6 million years ago - 2,00,000 years ago
9) Neanderthals - 4,00,000 to 40,000 years ago
10) Homo Sapiens- 40,000 to present
One of the evolutionary stages- The Neanderthal presently extinct were believed to have evolved in the old age Eurasia or otherwise the modern day African subcontinent . The Closest relatives appeared very similar to modern day humans and developed the process of thinking .They lived in the Pleistocene Enoch. Evidence of spiritual development was noticed in this stage.
Though they were shorter and stockier with angled cheekbones, prominent brow ridges, and wide noses, they were thought of as dumb brutes. Scientists have discovered that they used tools, buried their dead and controlled fire, among other intelligent behaviors.
The Neanderthals and the homo sapiens started mixing around 1,00,000 years ago until they went extinct. This was thought so because of the presence of Neanderthal DNA in humans. This piece of evidence strengthened the fact that Neanderthals and homo sapiens shared the Earth during their time.
Evolution in present ages
Evolution is a continuous process which occurs throughout the history and life of Earth. Life on Earth has developed from a single organism back in the mists of time, and perhaps even from one single common ancestral cell.The most recent common ancestor of all current life on Earth is estimated to have lived some 3.5 to 3.8 billion years ago.Life on Earth has suffered occasional mass extinctions like the Cretaceous - Palaeogene extinction event, Triassic - Jurassic event, Permian -Triassic event ,Late Devonian extinction and Ordovician-silurian events . But these mass extinctions has often accelerated the evolution of life on Earth. The worst extinction event was the Permian -Triassic which is said to have wiped off 90% of its species.
Recently researchers has concluded the presence of an ongoing mass extinction-the Holocene event mainly caused as a result of human activity.
Evolution is hidden and still ongoing among the living population. It is a process that can never be ceased. As life on Earth becomes harsher each day, so does the process of evolution.
© 2016 Stephy Varghese Thazhone
sikha on June 20, 2016: