Co-extinction is the fourth cause in NCERT's "Evil Quartet." It means: when a species becomes extinct, the plant and animal species tied to it in an obligatory (must-have) way also become extinct. Memory hook: think of a host fish dying, so its unique parasites die too, and a plant losing its only pollinator, so the plant can no longer make seeds.
Co-extinction: when an obligate host (species A) goes extinct, the parasite (species B) that depends only on it also disappears. The same happens between a plant and its sole pollinator.
Your doubts, answered
What exactly does 'co-extinction' mean in NCERT?
NCERT gives one plain line: 'When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct.' So the extinction of one species drags a second species down with it, because the second one cannot survive without the first. The key word is obligatory: the two are locked together.
What is a good example of co-extinction?
Two classic NCERT examples: (1) When a host animal (like a fish) goes extinct, the parasites that live only on that host also go extinct with it. (2) In plant-pollinator mutualism where one animal pollinates only one plant, if one partner dies out, the other soon follows. If a plant loses its only pollinator, it cannot set seeds and dies out too.
Why does the parasite die when the host dies?
An obligate parasite can complete its life cycle on only one specific host. It has no other place to feed, breed, or grow. So the moment that host species disappears, the parasite has no home left and also disappears. This is why host-parasite pairs are the textbook co-extinction example.
Is co-extinction the same as alien species invasion?
No. These are two different causes in the Evil Quartet. Alien species invasion is when a new outside species is introduced and harms native species (like Nile perch in Lake Victoria, or Clarias gariepinus in the Yamuna). Co-extinction is when the loss of one native species automatically causes the loss of another tied to it. Do not mix them up in matching questions.
Is co-extinction the most important cause of biodiversity loss?
No. The most important cause is habitat loss and fragmentation, which NCERT states clearly. Co-extinction is a real cause but is listed as one of the four, not the biggest. NEET repeatedly tests this: the answer to 'most important cause' is always habitat loss and fragmentation, not co-extinction.
⚠️ The NEET trap ✗ Marking co-extinction as the most important cause of species extinction. ✓ Habitat loss and fragmentation is the most important cause. Co-extinction is only one of the four causes in the Evil Quartet. 🧠 When the question says 'most important cause,' the answer is always habitat loss and fragmentation, never co-extinction.
Real NEET questions
NEET 2024
These are regarded as major causes of biodiversity loss:
A. Over exploitation
B. Co-extinction
C. Mutation
D. Habitat loss and fragmentation
E. Migration
Choose the correct option:
A · A, B, C and D only
B · A, B and E only
C · A, B and D only ✓
D · A, C and D only
Solution: The major causes of biodiversity loss (the Evil Quartet) are habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions. Of the listed items, A (Over exploitation), B (Co-extinction) and D (Habitat loss and fragmentation) are real causes, while C (Mutation) and E (Migration) are not. So option 3 (A, B and D only) is correct.
NEET 2016 · NEET 2019
Which of the following is the most important cause of animals and plants being driven to extinction?
A · Over-exploitation
B · Alien species invasion
C · Habitat loss and fragmentation ✓
D · Co-extinctions
Solution: Of the four causes in the Evil Quartet, NCERT explicitly names habitat loss and fragmentation as the most important cause driving animals and plants to extinction. Co-extinctions is a real cause but is not the most important one, so option C is correct and D is the trap.
NEET 2022
Habitat loss and fragmentation, over exploitation, alien species invasion and co-extinction are causes for:
A · Population explosion
B · Competition
C · Biodiversity loss ✓
D · Natality
Solution: Habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinctions are the four major causes of biodiversity loss, together called 'The Evil Quartet.' They are not causes of population explosion, competition or natality, so the answer is biodiversity loss (option C).
Solved Biodiversity and Conservation NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
