About the origin of life, several hypotheses have been put forth. Some of them, with their short explanation, are given below.
Theory of special creation
According to this theory, on the earth, life was created by supernatural power, the god. This theory has no scientific evidence; therefore, it is not widely accepted.
Theory of spontaneous generation
According to this theory, life originated on the earth from the non-living things spontaneously. It was believed that the mud of Nile River could give rise to living creatures like frog, toad, snake and crocodile; when warmed in sun.
Modern concept of origin of life
Modern concept was suggested by opera in 1930 AD. According to this theory, the first living cell arose from simple elements. Micro-molecules like carbon, hydrogen, oxygen, nitrogen etc. united to produce macro-molecules like proteins, carbohydrates, enzymes, nucleic acids etc. Then they interact to produce the first living cell by a process called abiogenesis. Abiogenesis means development of living things from non-living matter.
The series of related and gradual changes in plants and animals which occur due to the continuous variation is called organic evolution.
The major evidences that support the theory of organic evolution are listed below:
a) Evidences from the study of fossils or paleontological evidence.
b) Evidences from comparative morphology and anatomy.
c) Embryological Evidences.
d) Evidences from the study of vestigial organs.
e) Evidences from the geographical distribution of organisms.
f) Evidences from the connecting links.
Evolution is defined as the series of changes which occur, each step depending on what has gone before.
Or, Evolution can be defined as the descent with the modification.
Homologous organs are those organs which have a similar embryonic origin and basic plan but different function. The forelimbs of whale, horse, man, bat and bird are homologous organs.When the wings of a bird or bat are compared with the wings of an insect, it is found that they have similar functions but different in basic plans, such organs are analogous organs.
Fossils give the information about the past organisms that came into existence on the earth as fossils are the remnants of them. Now technologies like carbon dating and uranium dating help to know their age also. Thus, we can find out time period at which they existed, the climatic condition of that period etc. By studying fossils scientists have traced the evolutionary history of animals like horses, dog, cats, camels and human beings too. So, fossils are the strongest evidences of evolution.
All animals and plants cannot be fossilized. They need to have the following properties for fossilization:
a) The organisms should have hard parts in their body.
b) The remains of organism should be buried quickly under a thick layer sediments over millions of years.
The first step in organic evolution is ______.
presence of lightning and UV radiation
formation of organic molecules from inorganic molecules
none of these
the creation of prokaryotic cells
When was the opera suggested the Theory of Modern concept?