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Geography question from UPSC CSE-Prelims, 2026

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

Last updated Jun 5, 2026
Correct Answer: Option D — 3
The correct answer is (d) 3.

Why Statement 3 is the Correct Basis
The assertion describes a massive, prehistoric geological reorganization of the river systems in northern India during the Pleistocene epoch. The primary biological evidence for this interconnectedness is the presence of very closely related (historically considered the same or sister species) river dolphins in both the Indus and the Ganga river systems.

The Biological Mystery: The Indus and Ganga-Brahmaputra river basins are currently separated by a massive, dry land divide in Punjab and Haryana. Marine/river dolphins cannot travel across land.

The Geological Explanation: The presence of the Platanista dolphins (the Indus river dolphin and the Ganges river dolphin) in two completely separate, unconnected modern river systems proves that at some point during the Pleistocene period, these rivers were connected.

The River Capture: Tectonic uplifts and changing topography forced rivers like the Yamuna and Sutlej to radically shift their courses. At one point, they shared a common channel or tributary system, allowing the dolphins to migrate between what we now know as the Indus and Ganga basins before tectonic shifts permanently cut them off from each other.

Why the Other Options are Incorrect
Statement 1 is incorrect: The Nadi-Sukta (Hymn of Rivers) in the Rigveda is a text composed much later (Bronze Age/Iron Age) than the Pleistocene epoch. While it mentions rivers like the Sarasvati, Ganga, Yamuna, and Sutlej, it describes the geography of the Vedic period, not the deep-time geological shifts of the Pleistocene.

Statement 2 is incorrect: Robert Bruce Foote is famously known as the "Father of Indian Prehistory" for his groundbreaking discovery of Paleolithic stone tools (like the Pallavaram handaxe). He did not conduct the foundational geological or hydrological explorations regarding the Pleistocene course-shifting of the Sutlej and Yamuna to support this specific hydro-biological theory.

Therefore, the biological evidence of the river dolphins is the key basis for this geological assertion.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.

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UPSC CSE 2026 Prelims

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Exam UPSC CSE
Stage Prelims
Year 2026
Subject Geography
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