Evolutionary Biology
Life and its origin: There are various theories regarding origin of life.
Classical theories of the origin of life
- Special creation of life: It was proposed by Spanish priest father Saurez (1548-1671 AD). According to him the earth and different forms of life were created by supernatural power “the God”. According to Hindu mythology lord Brahma created the earth and living forms. The first man was Manu and the first woman is Shraddha. According to Christianity, first man is Adam and woman is Eve. How ever there are not enough scientific evidence for this theory.
- Cosmogeny origin of life: According to this theory, Life came on the earth from another planet in the form of small spores called panspermia. These panspermia could survive in high temperature. When the planet collided with the earth, panspermia came on the earth and developed in different form of life. As this theory has no scientific proof, this theory is not accepted.
- Spontaneous Generation of life: According to this theory, life could come from non-living things. Frogs, toads, snakes etc were believed to be created from mud. Parasites, beetles, flies etc arose from sweet and manures. Aphids and other insects arose under the influence of heat and moisture from plant juice. Fly maggots and some insects arose from flesh. Microorganisms arose spontaneously from air or water. It was also rejected when Pasteur’s theory was accepted.
- Theory of Biogenesis: It tells that the life was originated from the pre-existing life.
a)Redi’s Experiment: Francisco Redi (1626-1698 AD) determined that maggots (larva of housefly) could not be created from meat but the smell of meat could attracts the flies. For this, he performed an experiment by placing pieces of meats in 3 jars ‘A’ ‘B’ & ‘C’. Jar A was covered with a parchment paper, jar B was covered with muslin cloth and jar C was left uncovered. The meat start decaying in all jars but maggots appeared only in jars C. Thus, he demonstrated that maggots were not created by meat itself, they could be originated by the housefly who visited the Jar c.
Evolution of Life
Evolution: The process of formation of new organism or complex organism from the simple organism or pre-existing organism by the process of slow and gradual change is known as evolution. Due to the evolution, different varieties of living organism are present in this earth. For eg. formation of multi-cellular organism from simple unicellular organism or formation of more advance human species from the less developed animal like monkey.
Evidence of Evolution
1. Evidence of evolution from a comparative study of morphology and anatomy:
The comparative study of different organs of living organisms shows three types of morphology.
a. Homologous Organ: These organ which are internally similar but externally and functionally different are called homologous organ. Eg. Forelimbs of man, birds, reptile and frog are externally different but internally same. Presence of homologous organ in different organism provide the evidence of evolution.
b. Analogous Organ: Those organ which are externally and functionally similar but internally different are called analogous organ. For eg. Wings of butterfly, birds and bad. The wings of these animals perform the same function i.e flight but differ in their internal structure. Presence of analogous organ provides the evidence of evolution.
c. Vestigial organ : Functionally inactive but structurally reduced organs of the body are called vestigial organ. These organs were well developed and functional on their ancestor. In human, more than 100 of vestigial organs provide evidence of evolution. For eg. Canine teeth, ear muscles, abdominal muscle etc.
2. Evidence off evolution from paleontology:
The study of plants and animal fossils is known as paleontology. Study of fossils provides strong and direct evidence of evolution. For eg. fossils of ancestors of human indicate that modern man originated from a past monkey-like ancestor.
Types of fossils
Based on part of organism get preserved fossil are of following types:
a. Intact or entire fossil: The fossil preserved in the form of a whole body is known as an intact fossil. For eg. Fossil of a mammoth elephant is preserved in the ice of Siberia.
b. Petrified fossil: The fossil preserved in the form of a hard part of an organism is known as a petrified fossil. In this fossil, the soft part of the organism is lost but the hard part like bone is left behind.
c. Mould or cast: The fossil preserved in the form of the impression of an organism is known as mould or cast. Such fossils are formed only when the materials surrounding on the buried organism becomes hard.
d. Imprints (impression): The fossil preserved in the form of the footprint is known as an imprint.
3. Evidence of evolution from embryology:
The embryo is the developing stage of the zygote before the formation of a body structure. Study of embryos of different groups of vertebrates are similar in structure and process of development.
4. Evidence from biochemistry:
Different chemicals present in the body of all living organisms are the same and perform the same function. For eg. trypsin present in protozoa to mammalian is the same and performs same functions like growth and development. This similarity in chemicals indicates that they have the same ancestor and are different due to evolution.
5. Based on pattern of newly developing or degenerating character and their similarities and dissimilarities, they are classified into following types:
1. Convergent evolution
- The process where by organism that are originally dissimilar evolve similar character independently is known as convergent evolution.
- It takes place when different organisms have to adapt to a similar environment.
- Eg. Evolution of wings of butterfly, birds and bats.
2. Divergent evolution
- It refers to the evolutionary pattern in which a single or a common ancestor gradually develops into different lines of descendants. It is produced when a single parental stock adopt differently to the different new habitats
- For eg. Evolution of different animals of canidae family from a common canidean stock which includes tiger, lion, Wild cat etc.
Importance of fossils
1.Fossils record shows that certain species that existed in the past are now extinct.
- Some extinct species show similarities with the present day forms. For example mammoth existed ten thousand years ago were more or less similar with the present day elephant.
- Fossils helps to study the appearance of different species at different times.
- It also helps to construct the evolutionary history of organisms.
- It also helps to know the habits and behavior of extinct species.
- It also helps to study the form and structure of extinct animals.
Connecting link
- It refers to the organisms having intermediate characters between two or more than two groups.
- Eg. Archaeopteryx It is a fossils of reptiles bird recovered from the rocks of Jurassic period. It has the following characters:
i.It had a beak like bird but also had teeth and heavy jaw as a retiles
ii.It have forelimbs modified into wings like birds but at the tip of the wings it also had claws like reptiles.
