IB Biology HLProtecting BiodiversityPaper 1 & 2~10 min read
Causes of Extinction
Extinction is normal. What is not normal is the current rate, and the fact that one species is behind most of it. This page is about extinctions caused by humans — and about the three case studies you are expected to be able to discuss.
📚 What you need to know
Extinction caused by human activities is called anthropogenic extinction.
Scientists believe we are currently experiencing a mass extinction event, with human activities playing a large role.
There have been five mass extinction events in the past, so the current round could be the sixth.
Case study 1: the North Island giant moa — a large, flightless, herbivorous bird in New Zealand, hunted to extinction by humans by 1300.
Case study 2: the Caribbean monk seal — docile, easy to hunt on rocks, killed for its oil and meat, declared extinct in 2008.
Case study 3 is your own choice: a species from a local or familiar region that went extinct due to human activities.
You do not need Latin names in an exam.
Anthropogenic extinction
Definition
Anthropogenic extinction is extinction that has been caused by human activities
“Anthropogenic” simply means “made by humans”. Extinctions have always happened without us — the fossil record is full of them — so the word is there to separate the background rate from the extinctions we caused.
Scientists believe we are currently living through a mass extinction event, and that human activities are playing a large role in it. There have been five mass extinction events in the past, which is why this one is often called the sixth.
Case study 1: the North Island giant moa
The North Island giant moa was a large, flightless, herbivorous bird that lived in New Zealand until about the year 1300.
Humans arrived in New Zealand between 1200 and 1300.
It is thought that the moas were hunted to extinction by humans by 1300 — within roughly a century of people arriving.
The gap between the first two markers is the whole story. A species that survived for millions of years lasted about a century once people arrived.
A classification aside. The North Island giant moa was once thought to be several different species, because females were much larger than males and the size difference was mistaken for a species difference. It is a neat reminder that classification involves judgement, and that judgement affects extinction counts too.
Case study 2: the Caribbean monk seal
Caribbean monk seals lived in the oceans around the Gulf of Mexico and the Caribbean.
They were declared extinct in 2008, although it is believed they may have died out some time before that date.
Their docile nature and their habit of lying out on the rocks made them very easy for European colonists to hunt.
They were killed for their oil and meat.
The two species lived on opposite sides of the world and were nothing like each other. The list of reasons they died out is nearly identical.
If you can, add one line like this to a case study answer: these species evolved without human hunters, so they had no behavioural defence against one. It turns a list of facts into an explanation, which is what “discuss” questions are looking for.
Case study 3: your own choice
You need a third case study, chosen and researched by you. Use these criteria.
Requirement
What it means in practice
From a local or familiar region
Pick something from your own country or somewhere you know well, so the detail sticks
Extinct due to human activities
A natural extinction will not answer an anthropogenic extinction question
Same level of detail
Where it lived, what it was like, what humans did, roughly when it died out
Examples of extinct species from different parts of the world include the baiji (a river dolphin), the passenger pigeon, the paradise parrot, the golden toad, and the St Helena darter, a species of dragonfly.
🧠
Four facts per case study
Where it lived — What it was like — What humans did — When it went. Four W’s, three case studies, twelve facts. That is the whole revision job for this page.
Worked examples
WE 1
Explaining an anthropogenic extinction
Using a named example, explain what is meant by anthropogenic extinction. (3 marks)
Point 1: the definition
Anthropogenic extinction is extinction caused by human activities.
Point 2: the example
The North Island giant moa was a large flightless bird in New Zealand. Humans arrived between 1200 and 1300.
Point 3: the human cause
The moas were hunted for meat and were extinct by 1300, so their extinction was caused directly by human hunting.
Definition first, then a named species with a date and a human activitya named example means you must name the species — “a bird in New Zealand” will not score
WE 2
Why some species are more vulnerable
Suggest why the Caribbean monk seal was particularly vulnerable to hunting. (3 marks)
Point 1: behaviour
The seals were docile and showed no fear of humans, having evolved without human hunters.
Point 2: where they were
They hauled out on rocks in the open, in predictable places, so they were easy to find and to catch.
Point 3: the incentive
They were a valuable source of oil and meat for European colonists, so hunting continued at a high rate.
Easy to find, easy to catch, worth catching“suggest” means you can reason from the information; you do not need a memorised fact for every mark
💡 Exam tips
Prepare three case studies: moa, monk seal, and one of your own.
For each, know where, what, what humans did, and when.
Use the word anthropogenic and define it as caused by human activities.
Mention the five previous mass extinctions and that this could be the sixth.
Explain why a species was vulnerable, not just that it was hunted.
Latin names are not required; common names are fine.
⚠ Common mistakes
Choosing a third species that went extinct naturally. The question is specifically about human causes.
Picking a species with no available detail. You need enough facts to match the two given case studies.
Writing that extinction is always caused by humans. Extinction is a natural process; anthropogenic extinction is the human-caused subset.
Giving dates without a cause. A date on its own does not explain anything.
Wasting time memorising Latin names. They are not needed.
Up next: Ecosystem Loss — why losing a habitat does more damage than losing a single species, and the case studies to learn for it.
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