How Many Species Are There on Earth? IUCN and Robert May's Estimate
Biology · Biodiversity and Conservation · NEET
About 1.5 million plant and animal species have been described and named so far (IUCN, 2004). But many more are still not discovered, so scientist Robert May made a careful estimate that the total number of species on Earth is about 7 million. Memory hook: "1.5 known, 7 total (May)" — the small number is what we have counted, the big number is May's best guess.
Counted vs estimated species: IUCN (2004) has described about 1.5 million species, Robert May estimates about 7 million total, while extreme guesses reach 20-50 million. NEET tests the 1.5 million (described) vs 7 million (May's estimate) contrast.
Your doubts, answered
What is the difference between 1.5 million and 7 million species?
1.5 million is the number of species that have actually been discovered, described and named so far (IUCN, 2004). 7 million is Robert May's estimate of the total number of species that exist on Earth, including the ones not yet found. So 1.5 million = counted; 7 million = estimated total. This exact contrast is a favourite NEET question.
Who gave the estimate that there are about 7 million species on Earth?
Robert May. NCERT says his estimate is 'more conservative and scientifically sound' and places global species diversity at about 7 million. Remember the pair: Robert May -> 7 million. This is asked directly (NEET 2020) and in Match-the-column form (NEET 2024).
Why can't we know the exact number of species on Earth?
Because a very large share of unknown species live in the tropics, which are less fully studied than temperate regions. Scientists compare temperate-tropical species richness of a well-studied insect group and extrapolate that ratio to other groups. This gives only an estimate, not an exact count, so figures range widely.
What are the 20 to 50 million figures then?
NCERT calls 20 to 50 million the 'extreme estimates'. They are the high, less reliable guesses. Robert May's 7 million is the conservative, scientifically sound figure. In NEET, 7 million is the correct answer; 20 million and 50 million are distractors.
How does May's estimate connect to 'still waiting to be discovered'?
Since about 1.5 million are already recorded and May estimates about 7 million total, roughly 6 million species are still waiting to be discovered and described (NCERT states 'nearly 6 million species on earth waiting to be discovered'). This is why the tropics matter so much for undiscovered life.
⚠️ The NEET trap ✗ 1.5 million is the total number of species on Earth. ✓ 1.5 million is only the number described so far (IUCN 2004); the estimated total is about 7 million (Robert May). 🧠 NTA loves mixing 'described so far' with 'total estimate'. Read the question stem: 'described/recorded' -> 1.5 million; 'estimate of total/global diversity' -> 7 million (May). If the option list has 7 million AND 1.5 million together, they are testing exactly this trap.
Real NEET questions
NEET 2020
According to Robert May, the global species diversity is about
A · 50 million
B · 7 million ✓
C · 1.5 million
D · 20 million
Solution: NCERT states that a more conservative and scientifically sound estimate made by Robert May places global species diversity at about 7 million. 1.5 million (C) is the number described so far per IUCN 2004, and 20-50 million (A, D) are the extreme, less reliable estimates.
NEET 2024
Match List I with List II. A. Robert May B. Alexander von Humboldt C. Paul Ehrlich D. David Tilman | I. Species-Area relationship II. Long term ecosystem experiment using outdoor plots III. Global species diversity at about 7 million IV. Rivet popper hypothesis
A · A-III, B-I, C-IV, D-II ✓
B · A-I, B-III, C-II, D-IV
C · A-III, B-IV, C-II, D-I
D · A-II, B-III, C-I, D-IV
Solution: Robert May - global species diversity about 7 million (A-III); Alexander von Humboldt - species-area relationship (B-I); Paul Ehrlich - rivet popper hypothesis (C-IV); David Tilman - long-term outdoor plot experiments (D-II). Only option A matches all four.
Solved Biodiversity and Conservation NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
How many species are there on Earth according to NCERT?
About 1.5 million species have been described and named so far (IUCN, 2004), but Robert May's scientifically sound estimate puts the total at about 7 million.
Who is Robert May in biodiversity?
Robert May is the scientist who made the conservative, scientifically sound estimate that global species diversity is about 7 million. Remember: Robert May -> 7 million species.
What does IUCN stand for and what number did it give?
IUCN is the International Union for Conservation of Nature and Natural Resources. Per IUCN (2004), slightly more than 1.5 million plant and animal species have been described so far.
Why is 7 million called a conservative estimate?
Because extreme guesses range from 20 to 50 million. Compared to those, May's 7 million is a lower, more careful and scientifically defensible figure, so NCERT calls it conservative and scientifically sound.
How many species are still to be discovered?
With about 1.5 million recorded and about 7 million estimated total, nearly 6 million species are still waiting to be discovered, most of them in the tropics.
