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Forelimb of whale is called as Flipper.

(a) One auricle one ventricle

(c) Hugo de Vries

When we see fish, turtle, chicken, human embryo’s, early stages in them appears almost identical. This proves that the ancestors of all the vertebrates were almost identical. This proves that ancestors of all vertebrates resemble with fish and their development is certainly in order. Haeckel Theory: According to this theory, ” Every organism, in its development, repeats its organic history”. This theory is known as Theory of Recapitulation.

Darwin added new approaches to his old doctrine and gave a new doctrine of neo – Darwinism. According to this, new species are originated due to gene variation into the members of the particular species. Only genetic variations are inherited and environmental characteristics ends when animal die.

Evidences from Geographical distribution:

Now a days, variations are found in the geographical distribution of plants and animals. For example, Platypus. Kangaroo and Eucalyptus plant is found in Australia only. Similarly, Giraffe is found only in Africa. According to scientists at a time, the continents were connected to each other. Later on they were separated by the sea. That’s why animals and plants found in one continent could not reach to another continent Due to different circumstances structures of them are changed according to different places. The geographical distribution is therefore also certifies organic evolution.

The formation ofprimitive protein occurred as a result of chemical reaction between amino acids and carboxylic acid.

Organic evolution refers to the slow and gradual process by which living organisms have changed from the simplest unicellular form to the most complex multi-cellular forms that are existing today.

Life originated on Earth about 3.5 billion years ago. Life originated as a result of very slow and gradual process. Initially, the atmosphere of earth was reducing. The conditions favorable for life were there at that time which are not present now. Some amino acids were formed as a result of some chemical reactions. Primary simple cell is formed by some combination of amino acids which gave rise to different individuals.

Initially, unicellular organisms developed on Earth.

1. Reptiles 

2. Fossils 

3. Skeleton

4. Africa 

5. Hugo de Vries

No, all organisms were not the same as they are today. A lot of variations takes place from the very past till now and this gave rise to new species

(c) Hugo de Vries

According to Lamarck, the organs which are frequently used were developed more whereas the organs which were used less frequently perish. For example, as a result of more use of neck and fore limbs of African giraffe, these organs increase in size.

The principle oflnheritance of Acquired traits was given by: Lamarck

Charles Robert Darwin’s gave a theory of natural selection for organic evolution.

Different phases of Darwin’s theory are as under: 

1. Production of off spring in living organisms: Each organism does production of off springs to maintain their race. Example, elephant produces 8 off springs in her life span. It is a slow breeder. A pair of elephant began to breed regularly and engender that all off springs are regularly breeding in the 750 years a pair will generate approximately 1.9 million elephants and number of elephants will be very high. But this does not happen.

2. The struggle for survival: Due to over production of off springs, the struggle for space and food for the growing number of offspring takes place. It is the struggle of survival. This struggle occurs in between animals of own species; and with other species also which is capable of the same shall live. Destruction due to struggle, the number of organisms will remains balanced and consistence in nature.

3. Natural Selection: In struggle of survival only those animals live who adapt them according to nature. If they are not able to do it, then they are destroyed.

4. Origin of new species: Inheritance of useful traits will continue from generation to generation and harmful traits gradually become extinct or remains as Vestigial organ. Sometimes, variations increase so that after new generation is more different from older generation and development of a new race goes.

For example, at the beginning dog, jackal and wolves, three were members of the same race but due to change in atmosphere to adapt themselves accordingly, changes in their size and physical characteristics occurred, After thousands of years dog, fox and wolf, three new species were developed.

Dinosaur is extinct animal

Most developed group is Mammals.

1. Tonsils

2. Appendix.

Heart of a fish has two valves where as heart of a frog has three valves.

The solid evidence of evolution is Fossils

Some organs are found in animals today which are present in the form of remains. But they were highly developed and functional in their ancestors. Examples are as follows:

In both of them, skeleton is made up of vertebrae.

Comparative study of hearts of fish, frog, snake and man shows that structure of fish is simplest of all and structure of human heart is more complex. This shows a certain order of evolution. 

The table represents the same as:

Archaeopteryx.

We can see that digestive tract of frog, birds, man etc., have a pharynx, stomach, small intestine. It includes liver, pancreas, digestive glands etc. Secretion of digestive juices and their function is also same. So this proves that these animals have evolved in a certain order.

Generally, skeleton is found in no to chord animals. They have back bone which is made up of small bones called vertebrae. The similarity in their bones of hands and leg and skeletal systems, shows that their ancestors would have been similar. Over the time, some differences appear due to change in conditions.

Professor Birbal Sahni.

Theory of Mutation:

Hugo de Vries gave the theory of mutation. When he tested some plant, he found that some of the plants produced are quite different from their species. These traits are inherited from generation to generation. These sudden variations in inherited characters are called Mutation.

Mutation in animals can be caused by the following: 

1. Change in number of genes 

2. Change in gene arrangement 

3. Change in gene structure. 

Means of mutation: Mustard gas, Nitrous acid, Phenol, X – rays, Beta rays etc.

Palaeobotanist who enchanted the world with interesting tidbits, Birbal Sahni was bom on November 14, 1891 at Bhera village, in the Shahpur District. He is the founder of Palaeobotanical research in India. Among st a large number of fossil plants described by him from Rajmahal Hills of Bihar, was his most remarkable discovery of a new group of fossils Gymnosperms, to which he gave the name ” Pentoxylae”. Sahni was greatly interested in archaeology and he published a number of papers in this filed. His work “on the Technique of Casting coins in the ancient India” set a new standard in archaeological research in India. He founded the institute of Paleobotany at Lucknow, which was later renamed as Birbal Sahni Institute of Paleobotany after his death.

On earth, firstly single celled organisms were formed. Then multicellular organisms were originated from them. Earlier, these were simple, but in gradual development became complicated. All animals were initially without a back bone. Fishes grew from them, by which amphibians were developed. From these evolved reptiles who ruled on the earth millions of years. Thereafter, some reptiles developed into birds and other in mammals. Animals from one class to another takes thousands of years to develop. Similarly, the evolution in plants also take place.

This theory was given by Jean Baptiste Lamarck in 1809. His theory is known as Theory of Acquired traits. According to Lamarck due to changes in environment, more frequently used organ strengthened and organ that was less frequently used disappeared. Giraffes are found in Africa. It has long legs and neck. It lives by eating the leaves of tall trees. According to Lamarck ancestors of giraffe were not so tall. They could easily eat weeds. Gradually, due to changes in the environment, desert extended and grassland perished.

To get the leaves of the tress which were at height, legs and neck had to use more frequently. That’s why its legs and neck become too long. These traits are inherited from generation and generation. Snakes live in holes. Due to inconvenience legs were use less and gradually disappeared. Drawbacks of Lamarck: Some scientists denied the theory of Lamarck. They said,”if the tail of a mouse is cut generation to generation, there is no chance of birth of a mouse with out tail. In the same manner, girls do not take with a prick in their earlobe even after girls are having it from generations.

Those organisms which shows characteristics of two groups are called connecting links. For example, Archaeopteryx serves as a connecting link between reptiles and birds. This animal had some features like beak, wings, structure of legs etc similar to aves (bird) and some characteristics beak, tail, scales on body etc similar to reptiles.

(b) Reptiles and Aves