The concept of evolution
Compare a giraffe's long neck with a goat's short neck. Over very long periods, animals slowly change to suit the place where they live. That slow change is called evolution.
Evolution (उत्क्रांती) means gradual and continuous change. Helpful changes pass on to the next generations and a new species (नवी प्रजाती) may form.
Rule 1: How a new species forms — While surviving by adapting to environmental changes, certain internal physical changes occur in some animals of a species. Over time these become inherited characteristics in all following generations. The new species is usually more evolved than the original.
In the figure : In the figure helpful changes pass on to the next generations and slowly a new species forms.
- Easy : Easy: Evolution means slow change.
- Medium : Medium: Only changes passed to the next generation count.
- Exam-type : Exam: A new species is usually more evolved than the original.
Rule 2: Survival and extinction — Species that can adapt to environmental changes survive. The ones that cannot become extinct (नष्ट). Sometimes the original species dies out, and sometimes more than one species evolves from it. The first scientist to explain evolution systematically was Charles Darwin.
- Easy : Easy: Adapting animals survive.
- Medium : Medium: Species that cannot adapt may become extinct.
- Exam-type : Exam: Darwin first explained evolution in a systematic way.
Evolution = slow change. Adapt and survive, or become extinct.
Thinking an animal changes in one lifetime to become a new species. It takes many generations.
Memory clue: "जुळवणारे टिकतात".
Spot the difference
| Term | Meaning |
|---|---|
| Evolution | Gradual, continuous change |
| New species | Formed from inherited helpful changes |
| Extinct | Species that cannot adapt |
Practice questions
- 1What is evolution?
- 2What may form when helpful changes pass on for many generations?
- 3What does extinct mean?
- 4Who first explained evolution systematically?
- 5Which species survive?
- 6Can more than one species evolve from one species?
- 7Why can an adaptation not appear in one day?
- 8Why is a change useful only if it is inherited?
Show answers (try them yourself first)
- 1Gradual and continuous change.
- 2A new species.
- 3The species has died out completely.
- 4Charles Darwin.
- 5Those that adapt to environmental changes.
- 6Yes.
- 7It builds up slowly over many generations.
- 8Only then can the next generations also have it and a species can change.
Dinosaurs
Children love dinosaurs in cartoons and museums, but no one has seen a living dinosaur. We know them only from fossils found in rocks.
Dinosaur (डायनोसॉर) means "terrible lizard" (Greek deinos = terrible, sauros = lizard).
Rule 1: Giants that vanished — Many species of dinosaurs lived in ancient times, and some were enormous. The huge species suddenly became extinct, probably because of a sudden natural disaster or environmental change. One explanation is that a giant rock from space struck the earth about 66 million years ago.
- Easy : Easy: Dinosaur means terrible lizard.
- Medium : Medium: Some dinosaurs were enormous.
- Exam-type : Exam: The enormous species became extinct, probably due to a disaster.
Rule 2: From dinosaurs to birds — Fossils of winged dinosaurs have been found. Some two-legged winged dinosaurs are believed to have evolved into birds (पक्षी). So birds are still living relatives of dinosaurs.
In the figure : In the figure some winged dinosaurs are believed to have evolved into birds.
- Easy : Easy: Fossils tell us about dinosaurs.
- Medium : Medium: Winged dinosaurs left fossils.
- Exam-type : Exam: Birds are believed to have evolved from some two-legged winged dinosaurs.
Dinosaur = terrible lizard. Huge ones became extinct; some evolved into birds.
Saying all dinosaurs turned into birds. Only some winged two-legged ones are believed to have.
Memory clue: "मोठे गेले, पंखवाले उरले (पक्षी)".
Spot the difference
| Point | Dinosaurs |
|---|---|
| Meaning of name | Terrible lizard |
| Fate of huge ones | Became extinct |
| Link to today | Birds |
Practice questions
- 1What does dinosaur mean?
- 2From which Greek words does it come?
- 3What happened to the enormous species?
- 4Give a possible reason.
- 5Which living animals are believed to have evolved from winged dinosaurs?
- 6How do we know about dinosaurs?
- 7Why are birds called living relatives of dinosaurs?
- 8Why is it hard to say exactly why dinosaurs vanished?
Show answers (try them yourself first)
- 1Terrible lizard.
- 2deinos (terrible) and sauros (lizard).
- 3They suddenly became extinct.
- 4A sudden natural disaster or environmental change.
- 5Birds.
- 6From fossils found in rocks.
- 7Some winged dinosaurs evolved into birds.
- 8It happened millions of years ago and we have only fossils and rocks as clues.
Invertebrates and vertebrates
A snail has no bones but a fish has a backbone. We can sort all animals into two groups just by asking: does it have a backbone?
Life began with one-celled protozoa (प्रोटोझोआ). Invertebrates (अपृष्ठवंशी) have no backbone and vertebrates (पृष्ठवंशी) have a backbone.
Rule 1: First life — Life on earth began with unicellular organisms, the protozoa. Over time they gave rise to multicellular living things, which became more and more varied.
In the figure : In the figure life on earth started with one-celled organisms and became more varied over time.
- Easy : Easy: Protozoa have one cell.
- Medium : Medium: Multicellular organisms came later from unicellular ones.
- Exam-type : Exam: Life began with unicellular organisms.
Rule 2: Two groups of animals — Invertebrates have no backbone: snail, worm, mosquito. Vertebrates have a backbone: fish (aquatic), frog (amphibian, lives in water and on land), snake (reptile, crawls), birds and mammals such as the cow.
In the figure : In the figure animals are grouped by whether they have a backbone or not.
- Easy : Easy: A worm has no backbone.
- Medium : Medium: A frog is an amphibian.
- Exam-type : Exam: Fish, frog, snake, bird and cow are all vertebrates.
Invertebrate = no backbone. Vertebrate = backbone (fish, amphibian, reptile, bird, mammal).
Calling a snail a vertebrate. It has no backbone.
Memory clue: "कणा आहे = पृष्ठवंशी, कणा नाही = अपृष्ठवंशी".
Spot the difference
| Group | Backbone | Examples |
|---|---|---|
| Invertebrates | No | Snail, worm, mosquito |
| Vertebrates | Yes | Fish, frog, snake, bird, cow |
Practice questions
- 1With which kind of organisms did life begin?
- 2What is an invertebrate?
- 3What is a vertebrate?
- 4Give two examples of invertebrates.
- 5Name the five groups of vertebrates in the lesson.
- 6Why is a frog called an amphibian?
- 7Sort: snake, mosquito, cow, snail.
- 8Which is more varied now, life today or the first life? Why?
Show answers (try them yourself first)
- 1Unicellular organisms (protozoa).
- 2An animal without a backbone.
- 3An animal with a backbone.
- 4Snail and mosquito (or worm).
- 5Fish, amphibians, reptiles, birds and mammals.
- 6It lives both in water and on land.
- 7Vertebrates: snake and cow. Invertebrates: mosquito and snail.
- 8Life today, because unicellular life slowly gave rise to many multicellular forms.
Mammals
A calf drinks its mother's milk and a puppy does too. Milk-feeding is the sign of the most evolved group of vertebrates, the mammals.
Mammals (सस्तन प्राणी) are the most evolved vertebrates. The baby grows in the mother's womb and drinks her milk after birth.
Rule 1: Two signs of mammals — Most mammals have two features: (1) the baby grows in the mother's womb for some time before birth, and (2) the baby is fed on the mother's milk after birth.
In the figure : In the figure a mammal baby grows in the mother's womb and drinks her milk after birth.
- Easy : Easy: A cow is a mammal.
- Medium : Medium: A mammal baby drinks milk.
- Exam-type : Exam: A mammal baby grows in the womb before birth.
Rule 2: Egg-laying mammals — The platypus (प्लॅटिपस) and some kinds of spiny anteater lay eggs. They are still mammals because they feed their young with milk.
- Easy : Easy: The platypus lays eggs.
- Medium : Medium: Milk-feeding makes it a mammal.
- Exam-type : Exam: Egg-laying does not stop an animal from being a mammal.
Mammals: womb + milk. Platypus lays eggs but is a mammal.
Thinking that all egg-laying animals are not mammals. The platypus is an exception.
Memory clue: "सस्तन = दूध पाजणारे".
Spot the difference
| Point | Mammals |
|---|---|
| Before birth | Grows in the womb |
| After birth | Drinks mother's milk |
| Exception | Platypus lays eggs |
Practice questions
- 1Which are the most evolved vertebrates?
- 2Where does a mammal baby grow before birth?
- 3What does a mammal baby drink after birth?
- 4Name two mammals.
- 5Which egg-laying animal is a mammal?
- 6Why is the platypus a mammal although it lays eggs?
- 7Is a snake a mammal? Why?
- 8A bat flies but feeds milk to its young. Is it a bird or a mammal?
Show answers (try them yourself first)
- 1Mammals.
- 2In the mother's womb.
- 3The mother's milk.
- 4Cow and dog (any two).
- 5Platypus.
- 6It feeds its young with milk.
- 7No, it is a reptile that lays eggs and does not give milk.
- 8A mammal.
Apes and Darwin
At a zoo you see a gorilla and a chimpanzee sitting like us with hands that grip. They look like distant cousins of ours. Scientists say humans and apes have a common ancestor.
Apes (वानर, ape) are somewhat like humans and mostly lived on trees. Apes forced to live on the ground in grasslands evolved gradually into humans, first in Africa.
Rule 1: Down from the trees — Apes that stayed on trees kept their apelike form. Species that moved to the ground in grasslands evolved gradually into humans. The first human species is called the "primitive man" ("primitive" means the first).
In the figure : In the figure apes that began to live on the ground slowly evolved into humans in Africa.
- Easy : Easy: Apes lived mostly on trees.
- Medium : Medium: Apes that moved to the ground evolved into humans.
- Exam-type : Exam: Humans first evolved in Africa.
Rule 2: Darwin's ideas — Charles Darwin (1809–1882) sailed round the world on the ship HMS Beagle (1831–1836) and studied animals and plants on the way. He explained his theory in On the Origin of Species (1859). Its first printing sold out quickly. In 1871 he published The Descent of Man. Carl Linnaeus had classified animals earlier. Darwin noted that the last bone of the spine is a vestige (leftover) of a tail and that wisdom teeth also point to evolution. He accepted that humans evolved from tailless apes like the gorilla and chimpanzee of Africa.
- Easy : Easy: Darwin wrote On the Origin of Species.
- Medium : Medium: It was published in 1859.
- Exam-type : Exam: The tailbone and wisdom teeth are signs of evolution.
Ground apes in Africa became humans. Darwin: 1859 and 1871 books.
Saying humans came from monkeys at the zoo. Humans and apes share ancestors.
Memory clue: "झाडावर वानर, जमिनीवर माणूस".
Spot the difference
| Person/event | Year |
|---|---|
| Beagle voyage | 1831–1836 |
| On the Origin of Species | 1859 |
| The Descent of Man | 1871 |
Practice questions
- 1Where did apes mostly live?
- 2Where did humans first evolve?
- 3Who proposed the theory of evolution in a book in 1859?
- 4Name the book Darwin published in 1871.
- 5What is a vestige? Give an example.
- 6Who classified animals before Darwin?
- 7Why did apes that moved to the ground change over time?
- 8Humans did not come from the apes in a zoo. Explain.
Show answers (try them yourself first)
- 1On trees.
- 2In Africa.
- 3Charles Darwin.
- 4The Descent of Man.
- 5A leftover of an organ; the last bone of the spine (tail).
- 6Carl Linnaeus.
- 7Life in grasslands needed walking and using the hands, so helpful changes were passed on.
- 8Humans and apes evolved from a common ancestor; present apes are our distant relatives.
Quick revision
- Evolution = gradual change; adaptation helps survival; others become extinct.
- Dinosaur = terrible lizard; some evolved into birds.
- Vertebrates have a backbone; mammals are the most evolved.
- Apes on the ground evolved into humans in Africa.