Evolution and Principles of Systematics (2+1) The Origin Of Life Dr. Shahzad Ali Assistant Professor Department of Wildlife and Ecology UVAS, Ravi Campus, Pattoki

EVOLUTION WHAT IS EVOLUTION All the changes that transforms the life on earth

Origin of Life IT IS QUITE NATURAL TO ASK: 1. How life appeared on the Earth? 2. What was the first form of life? 3. When and where did it originate? 4. Did it originate only once, or have repeated origins taken place? We do not know the answers of these questions. All we can do is to make intelligent guess about its characteristics. Because, the question of the origin of life is not simple. It is not possible to go back in time and watch how life originated; nor are there any witnesses.

Origin of Life There is testimony, in the rocks of earth (?], but it is not easily read, and often this record is silent on issues carrying out for answers. Perhaps the most fundamental of these issues is the nature of agency or force that led to the appearance of the first living organisms on earth…… the creation of life.

Theories for the origin of life The various theories that have been offered to explain the origin of the life are as under: 1. Theory of Spontaneous Generation 2. Theory of Special Creation 3. Theory of Cosmozoa 4. Theory of Panspermia 5. Theory of Chemosynthesis (Phase I-VI)

Theory of Spontaneous Generation Until about 200 years ago, it was commonly believed that life could arise spontaneously from non-living matter Epicurcus ( BC) suggested that worms and other animals were generated from the soil or manure According to Aristotle ( BC) living creatures are born spontaneously Thus common worms, bee larvae, wasps, ticks and various other insects are born from dew, dry wood, cowdung, and rotten meal For the thousands of years, Egyptians believed that crocodiles could be formed from the mud of Nile river, scorpion from the cowdung and bacteria by decomposition. Van Helmont ( AD) gave a recipe….. Grains of wheat and dirty shirt if kept in a dark container for 21 days… produces mice spontaneously

Theory of Spontaneous Generation This theory, however is no longer valid. The formation of bacteria by decomposing matter and origin of insects or maggots in rotten meat or cowdung has been refused by the experiments by Pasteur (Great contribution in science) and Radi (what do you know about Radi Experiments) The great French scientist Luis Pasteur in 1862 AD confirmed what many other has suspected. All life today, including microbes, arise only by the reproduction of pre- existing life. (Cell theory??)

Theory of Special Creation Until the middle of 19 th century, life was presumed to be created by some super natural power or creator once or at successive intervals. This theory holds that all life forms have been specially designed and created by the creator or God This view point, common to most religion, including Islam is the oldest hypothesis The Biblical story of creation of life and world within six days was given by Spanish monk Father Suarez ( AD). He described that earth and heaven were created on the first day and sky on the second day. Plants and animals originated on the third day, while the sun, the moon and stars were created on fourth day; the birds and fishes appeared on fifth day and finally men and beasts were created on sixth day. The woman was constricted on seventh day from the 12 th rib of man

Theory of Special Creation According to Hindu methology, the world was created by God Brahama. Gods, men and devils developed from the head; birds from chest; goats from his mouth and plants from the hairs of the body. The religious point of views are based on the faith and are linked with belief and some divine force. These are not testable. Furthermore, the facts of modern biology doest not allow us to accept the theory of special creation

Theory of Cosmozoa It explains the presence of life on our planet i.e. Earth, by assuming that it was brought from elsewhere from the universe, perhaps, incorporated in some falling meteorite. According to this theory given by Richer (1865 AD) the life is distributed throughout the cosmos or universe in the form of resistant spores of living forms, the COSMIZOA. These may have been carried accidently through space from some other planet to this one Evidence of life on other parts of cosmos came from the discovery of fossils of micro-organisms in 1961 AD.

Theory of Cosmozoa But the explanation is unsatisfactory It is unlikely that the living matter could survive extreme cold and intense irradiation of inter-planetary travel And even life could withstand the rigors of inter-planetary travel, the theory does not answer our basic question How life came to exist on the planet?

Theory of Panspermia Crick and Orgel have revived the theory of Panspermia They assume that there are more modern civilization on other planet; and that inhabitants of such planet decided some thousands of millions of years ago to experiment whether life can developed in new environment in the neighboring planet or not. So they infected some planets on our galaxy, including earth with some micro-organisms. This theory, however, meets the same objections as raised for Cosmozoa theory (??)

Theory of Chemosynthesis This is the most widely accepted theory today This theory holds that the first proto-cells were products of a chemical evolution Once a proto-cell arose, biological evolution would have begun Biological evolution depends on the presence of genes that can replicate, mutate and control the characteristics of life The evidence for such an evolution is based on our knowledge of the primitive earth and on the experiments that have been performed in the laboratories of a number of workers. The hypothetical sequence of events that might have led to the origin of the first living call may be as follow (Fig 3.1)

Fig 3.1 Origin of the first eukaryotic cell Primitive earth cooling Gases energy capture Small organic molecules such as, amino acids, glucose, nucleotides, etc polymerization Macromolecules, such as, proteins, nucleic acids, etc plasma membrane Protocell Self replication Cell; reproduction Photosynthesis Autotrophic cell gives off oxygen Aerobic respiration Animal like heterotrophics

Phase I The abiotic synthesis and accumulation of organic molecules (monomers) such as, amino acid, sugars, hydrocarbons, simple nucleotides, etc. Phase II The joining of these monomers into polymers forming macromolecules such as, proteins, nucleic acids, etc Phase III The aggregation of abiotically produced macromolecules, into droplets or so call protocells or protobionts Phase IV The origin of heredity i.e. development of DNA and RNA in the primitive aggregates Phase V Evolution of photosynthesis Phase VI Evolution of eukaryotic cell