<P> The coelacanth, a fish related to lungfish and tetrapods, was considered to have been extinct since the end of the Cretaceous Period until 1938 when a specimen was found, off the Chalumna River (now Tyolomnqa) on the east coast of South Africa . Museum curator Marjorie Courtenay - Latimer discovered the fish among the catch of a local angler, Captain Hendrick Goosen, on December 23, 1938 . A local chemistry professor, JLB Smith, confirmed the fish's importance with a famous cable: "MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED". </P> <P> Far more recent possible or presumed extinctions of species which may turn out still to exist include the thylacine, or Tasmanian tiger (Thylacinus cynocephalus), the last known example of which died in Hobart Zoo in Tasmania in 1936; the Japanese wolf (Canis lupus hodophilax), last sighted over 100 years ago; the ivory - billed woodpecker (Campephilus principalis), last sighted for certain in 1944; and the slender - billed curlew (Numenius tenuirostris), not seen since 2007 . </P> <P> As long as species have been evolving, species have been going extinct . It is estimated that over 99.9% of all species that ever lived are extinct . The average lifespan of a species is 1--10 million years, although this varies widely between taxa . There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species . "Just as each species is unique", write Beverly and Stephen C. Stearns, "so is each extinction...the causes for each are varied--some subtle and complex, others obvious and simple". Most simply, any species that cannot survive and reproduce in its environment and cannot move to a new environment where it can do so, dies out and becomes extinct . Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unliveable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors . Extinction may occur a long time after the events that set it in motion, a phenomenon known as extinction debt . </P> <P> Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on nature and nurture . The question of whether more extinctions in the fossil record have been caused by evolution or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction, argues for a mathematical model that falls between the two positions . By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause . When concerns about human extinction have been raised, for example in Sir Martin Rees' 2003 book Our Final Hour, those concerns lie with the effects of climate change or technological disaster . </P>

Which of the following is a cause of background extinction