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University of Bristol
Wellcome Trust
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Click to enlarge:
Tree fern from Honduran rainforest
– this has hardly changed since the
Jurassic period – you will have seen
them on ‘Walking with Dinosaurs’.


It is generally agreed that the natural life span for a species is between 2 and 10 million years, although many do last much longer before becoming extinct e.g. the crocodiles have hardly changed since the dinosaurs.

Extinction of a species is always a concern as it is irreversible, and the loss of a species will mean the loss of unique combination of diversity at gene and organism level.  Because all species will eventually become extinct, those species at risk are said to be ‘threatened’.  Many species become extinct (especially the small and uninteresting ones), without being noticed.

Extinction of a species may be sudden or extend over a longer period of time, often more than an average human lifespan. Accurate data for extinction rates are difficult but some are shown in Table 1.4 on this site.
 View webpage

Over geological time, the appearance of new species has far exceeded the extinction of species (biodiversity has increased). But in recent time, the known rate of extinction (especially for birds and mammals) is far higher than the appearance of new species – this has resulted in a high number of ‘threatened’ species.

24% (1130) of mammal species and 12% (1183) of birds are globally threatened (figures for 2000)

The IUCN website keep a detailed database about the most ‘threatened’ species.
 View webpage (click on Summary Statistics for the data tables)

Each threatened species has a category which ends in extinction.

Category Status

  • Extinct
  • Extinct in the wild
  • Critically Endangered
  • Endangered
  • Vulnerable
  • Lower risk
  • Data deficient
  • Not evaluated

Well known examples of extinction include the Dodo and the American Passenger pigeon. Using the two following websites, write a short article on each, saying what it was, where it lived and why it became extinct.

  Benefits to man

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