Maharashtra Board Class 5 EVS Part II Chapter 4 Evolution PDF Download

4. Evolution

4.1 The Concept Of Evolution

The word 'evolution' is generally understood to mean 'gradual and continuous change'. Evolution in the plant and animal world can be explained in the following manner: In the process of survival by adapting to environmental changes, certain internal physical changes occur in some animals of a species. Over a period of time, these internal changes become inherited characteristics seen in all following generations. Thus, a new species with characteristics different from the original may be created. Such a species is usually more evolved than the original one. Sometimes, the original species dies out or becomes extinct. Sometimes, more than one species evolve from the original one. The first scientist to give us a systematic explanation of the concept of evolution was Charles Darwin.

Species which are capable of adopting to environmental changes are able to survive. The ones that cannot do so, become extinct in the process of evolution.

In ancient times, there were many species of a type of animal called dinosaur. 'Deinos' in Greek means 'terrible' and 'sauros' means 'lizard' or reptile. Dinosaur means a 'terrible lizard'.

Teacher's Note

Evolution means animals change slowly over many years. Just like how your great great grandmother looked different from you, animals also changed over time.

Exam Trick

Remember: Evolution = slow change over time. Animals that can adapt to change survive. Those that cannot adapt become extinct like dinosaurs.

Points to Remember

Evolution means gradual and continuous change in living things.
Animals adapt to environmental changes to survive.
Species that cannot adapt become extinct.
Charles Darwin gave the first explanation of evolution.
Dinosaurs were ancient animals that became extinct.

4.2 The Stages Of Evolution Of Animals

We have learnt in the previous lesson that life on earth began with unicellular organisms known as protozoa. These unicellular organisms gave rise to multicellular living things. The multicellular organisms evolved gradually and various classes of plants and animals came into being.

The following are the stages of evolution of animals:

1. Invertebrates

Animals without a backbone are called 'invertebrates', for example, a snail.

2. Vertebrates

Animals which have a backbone are called 'vertebrates'. Look at the ones given below:

Aquatic animals: Example, fish.

Amphibians: Animals which live in water and also on land, for example, a frog.

Birds

Teacher's Note

Invertebrates are animals without bones, like snails. Vertebrates have bones, like fish and birds. We also have a backbone so we are vertebrates too.

Exam Trick

Remember: Invertebrates = no backbone (like snails). Vertebrates = have backbone (like fish, birds, cows). You can feel your own backbone in your back.

Points to Remember

Life started with single cell organisms called protozoa.
Invertebrates are animals without a backbone.
Vertebrates are animals with a backbone.
Fish live only in water.
Amphibians can live in water and on land like frogs.

Reptiles

Animals which crawl, for example, a snake.

Mammals

Mammals are the most evolved animals among vertebrates. The following are the characteristics of most of the mammals:

1 Growth of the baby in the mother's womb for some time before birth.

2 The baby is fed on the mother's milk for some time after birth.

The platypus and some species of anteater are exceptions to this. They are considered mammals because even though they lay eggs, they suckle their young ones.

Teacher's Note

Mammals are animals like cows and dogs. They feed milk to their babies. Your mother also gave you milk when you were a baby.

Exam Trick

Remember: Mammals = milk. All mammals feed milk to their babies. This is the main thing that makes them mammals.

Points to Remember

Reptiles crawl and move on the ground like snakes.
Mammals are the most evolved vertebrates.
All mammals feed milk to their babies.
Babies grow inside mother's womb before birth.
Platypus and anteater lay eggs but feed milk to babies.

4.3 Apes

Apes are somewhat like humans in appearance. They mostly lived on trees. Those species of apes which continued to live on trees retained their original apelike form. However, in grasslands, some ape species were forced to move around on the ground. These species evolved gradually and in time, gave rise to the human species. This happened first on the African continent. The first human species is called the 'primitive man'. 'Primitive' means 'the first'. In the next lesson, we shall learn more about the evolution of the human species.

Teacher's Note

Apes look like humans but they are covered in hair and live in trees. Long long ago, some apes came down from trees and slowly changed into humans over many years.

Exam Trick

Remember: Apes evolved into humans. Some apes stayed in trees and stayed as apes. Others came to ground and slowly became humans over many, many years.

Points to Remember

Apes look similar to humans in appearance.
Apes mostly lived on trees in forests.
Some apes came down to live on the ground.
Apes on ground slowly evolved into humans.
The first human was called the primitive man.

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