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NCERT Solutions for Class 9th Social Science Chapter 4 Fig. 4.6, Skulls of early humans and modern humans — LET'S EXPLORE

Book page 66 Updated on2026-09-08

Q1.
Do you notice any changes in the shape or features of the skulls across different ancestors?
Answer

Yes — and the changes run in a consistent direction across the four photographs (a) to (d). Working from the labels the figure prints and from what is visible in the pictures:

Fig. 4.6Who, and what the caption saysWhat you can see in the skull
aHomo habilis — Olduvai Gorge, Tanzania and Kenya, 2–6 million years ago; made chopper stone toolsThe smallest braincase of the four; a low, sloping forehead; the face and jaws push forward below the eyes; large teeth
bHomo erectus — Eastern African Rift Valley, 2 million years ago; made handaxes and cleaversA bigger but still long and low braincase; a heavy, continuous brow ridge like a bar above the eyes; a broad flat face; no chin
cHomo neanderthalensis — Europe and Southwest Asia, till about 40000 years ago; made Middle Palaeolithic flake toolsA large, long skull; strong arched brow ridges over each eye; a big nasal opening and a mid-face that projects forward; forehead still sloping back
dHomo sapiens — living humans, 'the only human species living today on earth'A high, rounded, dome-like braincase; a vertical forehead; brow ridges almost gone; a small, flat, tucked-in face; smaller teeth and jaws

The three trends to state as your answer:

  1. The braincase grows and changes shape — not just bigger, but taller and rounder, rising above the eyes instead of stretching behind them.
  2. The brow ridges shrink — a heavy bone bar in (b) and (c) becomes barely a swelling in (d).
  3. The face pulls back under the braincase — the projecting muzzle of (a) becomes the flat vertical face of (d), and the teeth and jaws get smaller with it.
Why the tool column matters as much as the skull column. Read the two together and the figure makes an argument, not just a display: chopper tools go with the smallest braincase, handaxes and cleavers with a larger one, flake tools with a larger one still, and 'complex technologies' — the chapter's phrase — with Homo sapiens. The chapter's claim is that all human ancestors were tool makers, but it was the Homo sapiens that developed complex technologies. The skulls and the toolkits change together.
Read the dates carefully. Fig. 4.6 prints '2-6 million years ago' for Homo habilis and '2 million years ago' for Homo erectus, so the two overlap. That is not a misprint in the argument — the running text says plainly that 'different kinds of human ancestors co-existed at this time'. Evolution here is a branching bush, not a single line of one species replacing another. Fig. 4.6's own caption calls it a 'sequence', but the text is the better guide.
Q2.
Can you observe a gradual straightening of the face?
Answer

Yes. Compare the four skulls in profile-sense — how far forward the face sits under the eyes — and the change is steady:

a Homo habilis — face and jaws project strongly forward, like a muzzle
b Homo erectus — still projecting, but the face is broader and flatter, under a heavy brow bar
c Homo neanderthalensis — the middle of the face (nose and cheeks) still pushes forward, the forehead still slopes
d Homo sapiens — the face is tucked in and nearly vertical, sitting below a forehead that rises straight up
Direction of change: from a projecting muzzle to a flat, upright face.

What is straightening, exactly. Two separate movements produce the impression:

  • The forehead becomes vertical. In (a) and (b) the skull slopes back sharply from the brow; in (d) it rises almost straight. This is the braincase expanding upwards and forwards.
  • The jaws retreat. The teeth and jaws get smaller and move back under the eyes, so there is less muzzle to project. A chin appears in modern humans, where none of the earlier skulls has one.
The connection to what the chapter has already told you. The chapter links these species to increasingly capable tools, and tools do part of the work that jaws used to do — chopping meat, cracking bone, digging tubers, scraping skin. It notes that tools acted as 'extra-corporal limbs', doing what hands alone could not. A face that no longer has to be a heavy-duty processing machine can afford to become smaller and flatter, while the space above it is taken by a bigger brain. That is the reasoning behind the picture. Note that it is inference from a pattern, not something the fossils state — the fossils show the change; the explanation is the argument built on it.
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