UPSC Prelims 2026Question 11Ancient History

Consider the following assertion:
In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa.
Which of the following is/are the basis of the above assertion ?
1. The Nadi-Sukta of the Rigveda
2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
3. The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below:

Options

(a)1 only
(b)2 only
(c)1 and 2
(d)3 only

Correct answer: d

Decision rule

A geological claim needs physical or biological evidence; hymns, and scholars famous for a different field, are decoys however familiar their names sound.

Explanation

Correct Answer

(d) 3 only

Explanation of the Correct Answer

The assertion relates to a geological / palaeo-hydrological hypothesis: at some point in the Pleistocene period, river systems in north-western India may have changed course, causing a connection or river capture between the Indus and Ganga-Yamuna systems.

The strongest basis for this assertion is:

3. The presence of the same species of dolphins in both the Indus and the Ganga river systems

The Indus river dolphin and the Ganga river dolphin are closely related freshwater dolphins.
Their presence in two now-separated river systems suggests that, in the past, there may have been a hydrological connection between the Indus and Ganga river systems.
Such a connection could have occurred through river capture or shifting of tributaries like the Yamuna or Sutlej.
This biological evidence supports the idea that one river system may once have been connected with the other.

Therefore, only statement 3 is the correct basis.

Why Other Options Are Incorrect

Option	Verdict	Explanation
(a) 1 only	Incorrect	The Nadi-Sukta of the Rigveda mentions rivers, including Saraswati, but it is a literary source, not a geological basis for Pleistocene river shifting.
(b) 2 only	Incorrect	Robert Bruce Foote is mainly associated with prehistoric archaeology and the discovery of Palaeolithic tools in India, not with establishing this river-shift hypothesis through exploration of the Sutlej and Yamuna.
(c) 1 and 2	Incorrect	Neither the Rigvedic Nadi-Sukta nor Robert Bruce Foote’s work forms the main scientific basis for this specific assertion.
(d) 3 only	Correct	The presence of the same or closely related freshwater dolphin species in both the Indus and Ganga systems is biological evidence suggesting an earlier connection between the two river systems.

Relevant Supplementary Information

Basis of the River-Shifting Hypothesis

Evidence / Claim	Nature of Evidence	Relevance to Assertion
Same dolphin species or closely related dolphins in Indus and Ganga systems	Biological / zoological evidence	Suggests earlier river connection or exchange between river systems
River capture	Geomorphological process	Explains how one river or tributary may be diverted into another basin
Pleistocene river changes	Geological time-scale evidence	Indicates that river systems were not always fixed in their present courses
Sutlej-Yamuna shifts	Palaeo-channel hypothesis	Used to explain past links among Indus, Saraswati, Yamuna, and Ganga systems
Nadi-Sukta	Literary evidence	Useful for cultural geography, but not sufficient for this geological assertion

Important River Systems Mentioned

River / System	Present Association	Relevance in This Question
Indus	Flows mainly through Tibet, India, and Pakistan into the Arabian Sea	One of the two river systems compared
Ganga	Major river system of northern India flowing into the Bay of Bengal	Other major river system compared
Yamuna	Presently a major tributary of the Ganga	Hypothesized to have had earlier links with the Indus system
Sutlej	Presently a tributary of the Indus system	Hypothesized to have once shifted course or connected with Yamuna/Saraswati systems
Saraswati / Ghaggar-Hakra system	Palaeo-channel debate in north-west India	Often discussed in relation to river shifts, though not the direct answer here

Key Takeaways from the Tables

The question is about scientific basis, not merely literary reference.
Dolphin distribution is important because freshwater dolphins cannot easily move between isolated river systems today.
Their presence in both the Indus and Ganga systems suggests a possible ancient connection.
River capture and course shifting are common explanations for such biological distribution.
The Nadi-Sukta may help in reconstructing ancient cultural geography, but it does not prove Pleistocene river changes.

Point	Explanation
Dolphin evidence is central	Similar dolphins in Indus and Ganga systems support the idea of an earlier connection.
Nadi-Sukta is not enough	It is important for Vedic river references but not a scientific basis for Pleistocene river changes.
Robert Bruce Foote is not the key basis here	He is mainly associated with prehistoric archaeology in India.
River systems can shift over time	Tectonics, sedimentation, climate change, and river capture can alter river courses.
Sutlej-Yamuna-Ghaggar debates are interdisciplinary	They involve geology, archaeology, hydrology, biology, and textual studies.
Biological distribution can preserve river history	Freshwater species can indicate ancient links between now-separated river basins.

Context and Current Relevance

The question connects geomorphology, biology, and ancient river systems.
It is relevant to debates on the shifting courses of the Sutlej, Yamuna, Saraswati/Ghaggar-Hakra, and their relationship with Harappan settlements.
It shows how biological evidence, like river dolphin distribution, can help reconstruct ancient environmental history.

Table: Evidence Used to Reconstruct Ancient River Course Changes

Evidence Type	Example	What It Indicates	Limitations / Caution
Biological evidence	Similar freshwater dolphins in Indus and Ganga systems	Possible ancient hydrological connection between the two river systems	Needs support from geological and genetic studies
Geomorphological evidence	Palaeo-channels, abandoned river beds	Old river courses and river migration	Dating and interpretation can be complex
Sediment analysis	Sand, silt, mineral composition	Source region of ancient river deposits	Requires laboratory-based confirmation
Remote sensing	Satellite imagery of buried channels	Traces of dried or shifted river courses	Must be verified by field studies
Archaeological distribution	Harappan settlements along Ghaggar-Hakra region	Human settlement patterns near ancient water systems	Settlement distribution alone does not prove perennial river flow
Textual evidence	Nadi-Sukta of Rigveda	Cultural memory of rivers and river importance	Not sufficient by itself for geological reconstruction
Zoological distribution	Species found in separated basins	Earlier river connection or river capture possibility	Species similarity may need genetic confirmation
Tectonic evidence	Uplift, subsidence, faults	Possible cause of river diversion	Needs correlation with river history

Table: Key Rivers in the Indus-Ganga River-Shifting Debate

River / System	Present Course	Role in River-Shifting Debate
Indus	Flows through Tibet, Ladakh, Pakistan into Arabian Sea	One major river system compared with the Ganga system
Ganga	Flows through northern India into Bay of Bengal	Major eastern river system compared with the Indus
Yamuna	Presently joins the Ganga at Prayagraj	Hypothesized by some scholars to have once flowed westward or had connections with the Indus/Saraswati system
Sutlej	Presently joins the Indus system through Punjab	Hypothesized to have once contributed to the Ghaggar-Hakra/Saraswati system or shifted course
Ghaggar-Hakra	Seasonal river / dry channel system in India and Pakistan	Often linked with palaeo-channel and Saraswati debates
Saraswati	Mentioned in Vedic literature; debated identification	Often connected with Ghaggar-Hakra and ancient river-course discussions
Beas	Tributary of Sutlej/Indus system	Important in north-western river network changes
Drishadvati	Vedic river, uncertain identification	Often discussed with Saraswati in ancient geography

Table: Dolphin Evidence and River Connection

Point	Explanation
Freshwater dolphins are river-bound	They generally cannot move freely across land or isolated basins.
Same or closely related dolphins in two river systems	This may suggest that the river systems were once connected.
Indus and Ganga systems are now separate	Their present separation raises the question of how similar dolphins occurred in both.
Possible explanation	Earlier connection through river capture, shifting tributaries, or palaeo-channels.
Why this matters	Biological distribution becomes indirect evidence of ancient river history.

Table: Literary vs Scientific Evidence

Evidence	Nature	Usefulness	Caution
Nadi-Sukta of Rigveda	Literary / textual	Gives names and cultural importance of rivers	Cannot by itself prove Pleistocene river shifts
Archaeological sites	Material evidence	Shows where ancient people lived and used resources	Does not automatically prove exact river courses
Dolphin distribution	Biological evidence	Can suggest ancient water connectivity	Needs scientific correlation
Palaeo-channel mapping	Geographical / geological	Helps trace old river beds	Requires dating and field verification
Sediment studies	Geological	Can identify source rivers and flow history	Technically complex and context-dependent
Oral / mythic traditions	Cultural memory	May preserve old geographical associations	Not reliable as independent scientific proof

Table: Related Concepts

Concept	Meaning	Relevance
Pleistocene Period	Geological epoch before the Holocene, marked by climatic fluctuations	Period during which major river changes may have occurred
River capture	One river diverts the flow of another river into its own basin	Explains how tributaries may shift from one river system to another
Palaeo-channel	Abandoned or ancient river channel	Helps identify former river courses
Drainage basin	Area drained by a river and its tributaries	River shifting changes basin boundaries
Tectonic activity	Earth movements due to faults, uplift, or subsidence	Can alter river courses
Alluvial plain	Flat land formed by river deposits	River migration is common in such plains
Endemism	Species restricted to a particular region or river system	Useful for reconstructing biological history
Biogeography	Study of distribution of species	Helps infer past geographical connections

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