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The first scientist to give us a systematic explanation of the concept of evolution was Charles Darwin

Human appendix is the remnant of caecum which is functional in the digestive tract of herbivorous animals like rabbit. Cellulose digestion takes place in the caecum of these animals. Due to change in the diet containing less cellulose, caecum in human became functionless and is reduced to a vermiform appendix, which is vestigial.

According to Darwin, the fitness of an organism is measured by its reproductive ability. Also the appearance of new forms is linked to the lifespan of an organism. The greater its lifespan, the more it can reproduce and hence, greater new forms would appear. This can be observed in the development of dark-winged moths due to industrial melanism.

Excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/ cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. These are examples of evolution by anthropogenic action.

Structures that are of no use to the possessor, and are not necessary for their existence are called vestigial organs. Vestigial organs may be considered as remnants of structures which were well developed and functional in the ancestors, but disappeared in course of evolution due to their non-utilization. 

E.g: Human appendix.

1. Platypus and some species of anteaters are exceptions to the characteristics of mammals. 

2. Though they lay eggs, they suckle their young ones. 

3. Therefore, they are considered mammals.

The characteristics of most of the mammals are as follows:

1. Growth of the baby in the mother’s womb, sometime before birth. 

2. The baby is fed on the mother’s milk for sometime after birth.

1. Apes are somewhat like humans in appearance 

2. They mostly lived on trees. Those species of apes which continued to live on trees retained their original ape like form. 

3. Some ape species found in grasslands were forced to move on the ground. 

4. These species evolved gradually, giving rise to the human species. 

5. This happened first on the ‘African continent’.

1. human 

2. primitive 

3. the first

The first systematic explanation of the concept of evolution was given by Charles Darwin.

There are two stages of evolution of animals. They are: 

1. Invertebrates: These are animals without a backbone. 

2. Vertebrates: Animals which have a backbone are vertebrates. Aquatic animals, amphibians, birds, reptiles and mammals are all vertebrates.

1. Life on earth began with unicellular organisms known as protozoa. 

2. These unicellular organisms gave rise to multicellular living things.

3. Multicellular organisms evolved gradually and thus various classes of plants and animals came into being

Mammals are the most evolved animals among vertebrates

1. birds 

2. multicellular 

3. invertebrates 

4. Vertebrates 

5. Amphibians

1. Dinosaurs became extinct because of some sudden natural disaster or environmental change 

2. Fossils of dinosaurs with wings have been discovered 

3. It is thus believed that some species of two legged and winged dinosaurs evolved into birds.

Unicellular organisms gave rise to multicellular organisms which in turn gradually evolved into various classes of plants and animals.

Amphibians live in water and also on land.

1. evolution 

2. physical 

3. extinct 

4. original 

5. Charles Darwin

The species that cannot adapt to environmental changes become extinct in the process of evolution

Fossils of dinosaurs with wings have been discovered. Hence, it is supposed that some species of two-legged and winged dinosaurs evolved into birds.

Dinosaur means a ‘terrible lizard’.

The first human appeared on the African continent.

In the process of survival by adapting to environmental changes, certain internal physical changes occur in some species of animals. Over a period of time, these changes become inherited characteristics seen in all subsequent generations. Thus, in the course of time, a new species with characteristics different from the original species is created.

Some sudden natural disaster or environmental change is believed to be responsible for the extinction of dinosaurs.

The species of dinosaurs, which were enormous in size, suddenly became extinct, because –

1. According to Darwin, the species that cannot adapt to environmental changes become extinct in the process of evolution. 

2. Some sudden natural disaster or environmental change is believed to be responsible for the extinction of enormous dinosaurs.

When DDT was used for the first time, maximum mosquitoes died but few survived due to variation in the population. These mosquitoes showed resistance to DDT and survived to reproduce successfully in the presence of DDT and gradually such mosquito population became DDT resistant due to natural selection.