UPSC Prelims 2026 Q11: Pleistocene River Shifts — Indus & Ganga
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
- 1 only
- 2 only
- 1 and 2
- 3
Answer: (d) 3
Statement-wise explanation
- 1: incorrect — The Nadi-Sukta (also called Nadistuti, Rigveda Book 10, Hymn 75) is a hymn in praise of rivers. It names them roughly from east to west: Ganga, Yamuna, Sarasvati, Shutudri (Sutlej), Parushni (Ravi) and so on, ending with the Sindhu (Indus). It records the rivers as Vedic people knew them in the 2nd millennium BCE. The Pleistocene ended about 11,700 years ago, long before any text existed, so the hymn cannot tell us about river courses in that period.
- 2: incorrect — Robert Bruce Foote was a geologist with the Geological Survey of India. He is called the father of Indian prehistory because he found the first Palaeolithic hand-axe in India in 1863, at Pallavaram near Madras (Chennai). Most of his fieldwork was in south India. He made no exploration of the Sutlej and the Yamuna that showed these rivers had shifted, so this statement is invented.
- 3: correct — Blind river dolphins of the genus Platanista live in both the Indus and the Ganga–Brahmaputra systems. They cannot survive in the sea, so the only way they could be in both basins is through an old freshwater link between the two systems. In 1919 the geologists Pascoe and Pilgrim used this as biological evidence that the Indus and Ganga drainages were once joined and later split. The two populations were then treated as one species. Today the IUCN lists them as two species: Platanista gangetica in the Ganga and Platanista minor in the Indus.
How to eliminate
Start with time. The Pleistocene ended about 11,700 years ago, and the Rigveda was composed around 1500–1000 BCE. A text cannot record river courses from thousands of years before it was written, so statement 1 goes out. That removes the two options that include it. You are left with 'Foote's explorations' or 'dolphins'. Ask which one could prove that two river basins were once connected. An animal that lives only in fresh water and is found in two basins now separated by land is the standard evidence for an old river link or river capture. If you also remember Foote only as the man of the Pallavaram hand-axe (1863), statement 2 falls away too. Facts to remember: Platanista river dolphins live in both the Indus and the Ganga, and Pascoe and Pilgrim proposed the Indo-Brahm river in 1919.
Know more
The Indo-Brahm (Shiwalik) river and how it broke up
NCERT (Class 11, India: Physical Environment, Ch. 3) describes a huge river, the Shiwalik or Indo-Brahma. It flowed along the whole length of the Himalaya from Assam to Punjab and into Sind, and emptied into the Gulf of Sind during the Miocene, about 5–24 million years ago. The evidence is the continuous Shiwalik deposits of sand, silt, clay, boulders and conglomerate. In the Pleistocene, uplift in the western Himalaya, including the Potwar Plateau (Delhi Ridge), broke this river into three systems:
| Part | Present system |
|---|---|
| West | Indus and its five Punjab tributaries |
| Centre | Ganga and its Himalayan tributaries |
| East | Brahmaputra in Assam and its Himalayan tributaries |
Why dolphins matter. River dolphins cannot live in the sea, so they cannot swim around the coast from one basin to another. Finding them in both the Indus and the Ganga points to an old freshwater link between the two. Pascoe and Pilgrim (1919) used this point when they proposed the Indo-Brahm river.
| Ganges river dolphin | Indus river dolphin | |
|---|---|---|
| Scientific name | Platanista gangetica | Platanista minor |
| Range | Ganga–Brahmaputra–Meghna systems (Ganga, Yamuna, Chambal, Gandak, Ghaghara, Kosi, Brahmaputra) | Indus in Pakistan; a small population in the Beas, Punjab |
| IUCN status | Endangered | Endangered |
| India | National Aquatic Animal | Very small, isolated population |
The two populations were long treated as subspecies of a single species. That is why older texts speak of the 'same species'.
The Yamuna and the Sutlej as border rivers. Both rise close to the Indus–Ganga water divide. Geologists think the Sutlej may once have flowed east and the Yamuna west into the lost Sarasvati/Ghaggar system before each was captured by its present basin. This is why the Sarasvati debate keeps coming back.
NCERT Concepts to Revise
- Indus river: The assertion asks whether the Indus system once exchanged rivers with the Ganga system, so it helps to know the Indus basin and its Punjab tributaries, including the Sutlej.