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UPSC Prelims 1993 · Environment · Nature’s Machinery
Which one of the following does provide the best estimate of world's biological diversity?
- (a) Of about ten million species probably alive today, some 20 species are lost every day, most of them unknown because no more than half a million have yet been actually identified by scientists
- (b) Of about thirty million living species, some 50 are lost every day, most of them unknown because no more than one million have been actually identified
- (c) Of about forty-five million living species, some 100 are lost every day, most of them unknown because no more than 1.5 million have been actually identified
- (d) Of about seventy-five million living species, some 500 are lost every day, most of them unknown because no more than 3 million have been actually identified
Show the answer and explanation
Answer: (c) Of about forty-five million living species, some 100 are lost every day, most of them unknown because no more than 1.5 million have been actually identified
About 1.5 million identified is the accepted count of named species; tens of millions in total and around a hundred lost a day matched the estimates of the time.
The idea
Nobody knows how many species exist; that part of each option is a guess. The one number scientists can count is how many species have been named and described. Use that to judge the options.
Named species in the early 1990s: about 1.5 million → Only one option has that figure → Answer (c)
Why the others are wrong
(a) “Only half a million identified” is far too low — scientists had named about 1.4–1.5 million species by the 1990s.
(b) One million identified is still below the real figure.
(d) 3 million identified is double the real count.
The trap
The totals are guesses, so don’t judge on them. Judge on the one hard number — species already described (~1.5 million then; ~2.1 million today).
Also know
A widely quoted 2011 study estimated about 8.7 million species in all, which means most are still unnamed. More than half of all named species are insects. India has about 7–8% of the world’s recorded species and is one of 17 mega-diverse countries.
🔒 Named species ≈ 1.5 million (1990s), ~2.1 million today; the total is estimated at ~8.7 million (2011) or more.