Grade 10 Biology (ICSE)

1. HUMAN EVOLUTION

2. What is evolution?
• Evolution is a slow and continuous process whereby complex forms of
life have emerged from simpler from through millions of years

3. Theories of evolution
1.Lamrckism/inheritance of acquired characters
-jean baptiste Lamarck
-advantageous changes influenced by the environment are passed on to their offsprings
2. Theory of natural selection
-Charles Darwin, English scientist
-completetion
-struggle for existence
-in a species, there is variation between individuals
-some individuals are more likely to adapt and survive than others- survival of the fittest
-these individuals more likely to survive and pass on their good qualities to the offsprings
-this process is called natural selection
-nature selects the fittest and rejects the weaker

4. Lamarck’s theory of inheritance of acquired
characters
1. Use and disuse
-parts of the body that are used extensively become larger and stronger
and those that are not used deteriorate
-explained by example of giraffe,he suggested that:
• giraffes evolved from ground feeding herbivores
• At later stage, area fell short and thus giraffes fed from trees
• Constant stretching of neck and fore limbs over many generations resulted
• in these structures becoming longer and stronger
2.Inheritance of acquired characters
-stated that organisms pass its modifications to its offsprings

5. Vestigial organs
1. Wisdom teeth
-last molars on each side of both the jaws
-appear at age of 17-20
2.Vermiform appendix
-projects from blind end of caecum(part of large intestine)
-narrow worm like tube
-functionless organ in humans
-corresponding organ in herbivores is helpful in digesting cellulose
3.Pinna
-we cannot move pinna to gather sound waves which is its main function in other
mammals(elephants)

6. Darwin’s theory of natural selection
The theory of natural selection or Darwinism is based on certain observable facts:
1. Overproduction
• Oysters lay60-80 million eggs in a single spawn
• Paramecium divides at the rate of three times in 48 hours
• Elephant is the slowest breeder , it produces 6 young ones in its lifetime of 90 years
2. Struggle for existence
-individuals multiply in geometric ratio whereas food and space remain constant
-this leads to struggle for existence and competition
-competition may be interspecific or intraspecific
3.Variation
-may be harmful or advantageous
4.Survival of the fittest
-nature selects those variations that are suitable
-this is what Darwin termed as natural selection
Speciation – origin of new species by gradual modification

7. Industrial melanism- an example of natural selection
• Before industrial revolution
-Lighter variety abundant because they camouflaged
-Well with lichen covered trees
-Darker variety rare because they were easily visible and
hence eaten up by birds
• After industrial revolution
-Lichen on trees died and tree darkened due to soot
-Now the dark variety was better hidden and not easily picked by
birds
-Lighter variety visible and hence their number declined
Biston betularia
Biston carbonaria

8. Lamarck vs Darwin
Lamarck s theory Darwins theory
1.Theory of inheritance of acquired characters 1. Known as the theory of natural selection
2.Use and disuse of organs . Parts used or changes
acquired get transmitted to next generation
. 2. Believes that since variations exist in individuals,
only the fittest survive in the struggle for existence.
Darwin is still
. 3. New species evolve after a long period of time
after many generations by acquiring new characters.
3. New species evolve due to accumulation of
favourable variations over a long period of time
neo darwinism:
• darwin was unable to explain source of variations
• modern genetics has revealed sources of variations
• darwins original theory of natural selection was modified.this theory is termed as neo darwinism

9. HUMAN EVOLUTION
• Karl Linnaeus gave man the scientific name Homo sapiens
• Homo sapiens or modern man belongs to the order Primates.
• Ramapithecus – the prehumen ancestor
• Ramapithecus walked erect on its hind feet, only had few teeth
and some fragments of jaw.

10. HUMAN EVOLUTION
• Going from an ape-like form to human form required many major
changes.
• These changes includes the following:
• Bipedal locomotion, increase in cranial capacity, reduction in the size
of canines, loss of jaw power, development of chin, development of
fore head and brow ridges, increase in height, erect posture by the
development of the lumbar curve, reduction in body hair.

11. HUMAN EVOLUTION
Human ancestors
Australopithecus
• small stature (3.5-4 ft tall)
• cranial capacity- 450-600cc
• vertebral column with lumbar curve, broad
pelvis
• man-like teeth
• Semian gap( A gap present in apes between
incisors and canines on either side of the jaw)
absent.
• Prognathous (Protruding outward)
face, chin absent
• eyebrow ridges projected over eyes

12. HUMAN EVOLUTION
Human ancestors
Homo habilis
• first man like ancestor
• 4.5-5 ft tall
• cranial capacity- 680-735 cc
• hairy body
• small canines like modern man.
• bipedal locomotion

13. Homo erectus
• 5-5.5 ft
• cranial capacity-800-1125 cc
• 1st ancestors to hunt animals and use fire
• walked fully upright
• pelvis was more bowl shaped
• stood erect
• proportions of arms and legs resembled that of modern man
• receding forehead, projecting jaw, chin absent
Neanderthal man
• 5.5 ft
• cranial capacity- 1450cc
• absolute bipedalism
• large head broad-flat and sloping forehead, prominent brow ridges, almost no chin and less
hair on the body.
• The classical Neanderthals were found in Western Európe, North Africa and Asia
• Homo sapiens is believed to have arisen from the main Neanderthal population and
developed into Cro-Magnon.

14. 5.cro-Magnon
• 30,000 years ago
• in europe
• more advanced than neanderthal
• 180 cm (5-5-6 feet) in height
• cranial capacity about l450 cc-1600 cc.
• large skull, broad face, rounded forehead and a prominent chin.
• They lacked eyebrow ridges , body Was less hairy, face was perfectly Orthognathous.
• Orthognathous- straight and strong jaw.
• with man-like dentition
• They were swift footed and cave-dwelling beings.
• Cro-Magnon made tools from finely chipped stones.
• They were good hunters and knew how to use the hide of animals, but did not know
agriculture and domestication.

15. Homo sapiens sapiens (modern man)
Man of today first appeared about 11000 years ago in the region around the
caspian and mediterranean sea
They possessed the following characters:
1. bipedal locomotion
2. 4 reversed curves in the spine
3. upright head, binocular vision
4. cranial capacity- 1450-1600 cc
5. straight limbs. shorter forelimbs, longer hindlimbs
6. steep forehead, reduced brow ridges
7. well developed,prominent chin
8. reduced body hair
9. entirely erect posture
10. Thoracic region flatenned into broad chest by flattening of sternum
11. logical and syllabic speech for communication