Official UPSC Format

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 :

⚡ Quick Recall Snippet

Geologists theorize that during the Pleistocene epoch, the Yamuna and Sutlej rivers shifted, breaking apart a massive ancient river (the Indo-Brahma) into the separate Indus and Ganga basins. A primary basis for this paleogeographical assertion is biology: the presence of nearly identical species of blind river dolphins trapped in both isolated river systems proves they were once physically connected.

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Detailed Solution & Authority Citations

Correct Answer is Option D
The assertion describes the geomorphological theory of the Indo-Brahma (or Shiwalik) River—a massive ancient river that geologists believe was broken apart into the modern Indus and Ganga systems due to tectonic uplift (like the Delhi Ridge) during the Pleistocene epoch.
Let's evaluate the evidentiary basis for this theory:
  • Statement 1 is Incorrect: The Nadi-Sukta of the Rigveda indeed names these rivers, but it was composed during the Holocene (recent human history, approx. 1500 BCE). The Pleistocene epoch ended over 11,000 years ago. Therefore, a human text cannot serve as the primary scientific basis for a pre-human geological event.

  • Statement 2 is Incorrect: Robert Bruce Foote is a legend in Indian archaeology, famous for discovering Paleolithic stone tools (handaxes) in 1863. He was not a paleogeographer focused on mapping the tectonic shifting of the northern Himalayan river systems.

  • Statement 3 is Correct: This is a classic example of biogeography validating geology. Freshwater river dolphins physically cannot cross land or survive in the salty ocean. Finding two closely related, highly specialized species of blind river dolphins (Platanista gangetica minor and Platanista gangetica gangetica) in two river systems that are currently completely physically isolated proves that, at some point in geological history, the Indus and Ganga basins were a single, continuous, connected waterway.
    • Conclusion: Only biological distribution (Statement 3) provides the scientific basis for the assertion.

    🚨 The Examiner's Trap

    The examiner uses chronological mismatching to trick candidates. Option 1 sounds plausible because the Vedas mention these rivers, but the Vedas are only 3,500 years old, whereas the assertion is about the Pleistocene epoch (millions of years ago). Option 2 uses a famous name (Robert Bruce Foote), but he studied stone tools, not river mapping.

    Active Recall Flashcard

    Tap to Flip

    What specific biological anomaly provides evidence for the geological theory that the Indus and Ganga river basins were once a single, connected river system?

    The presence of closely related species of blind river dolphins in both completely separated basins.

    Concept Flow Mapping

    Indo-Brahma River
    Separated Into
    Indus and Ganga Basins
    River Separation
    Occurred During
    Pleistocene Epoch
    Indus and Ganga Dolphins
    Provide Proof Of
    Past Geological Connection

    Logic Quest

    "Why does the dolphin prove geological history?"

    Not analyzing core concepts like Biogeographical Evidence for Paleogeography through the lens of Previous Year Questions is a serious miss-out. This PYQ engine is specifically designed to help you decode the examiner's mindset and master highly probable Physical Geography questions for your upcoming Prelims.