Evolution is as old as time itself: species adapt to cope with a changing environment, and new species emerge while the least adaptable ones die out. There were at, least five great mass extinctions in prehistory. The most recent – a mere 65 million year- ago – is the best known, for it wiped out all those impressive dinosaurs. In more recent times – for the past 50,000 years or so – the process of extinction has continued with more than a little active assistance from the burgeoning human race. In this context it is estimated that 99.9 per cent of all species that ever lived have become extinct.
Extinction is defined as the moment when the last living specimen dies, though in practice a species is doomed when the breeding population is reduced below a sustainable level. This can happen for many reasons, including climate change and failure to compete as more effective species evolve over time. But the pace with which human activity has already contributed to the extinction of species since the start of the 19th century is truly horrifying and, even more worryingly, species extinction appears to be happening at an ever-increasing rate.
Much to the dismay of conservationists, wholesale habitat destruction and global warming threaten imminent mass extinctions. On a practical level, many endangered species are now subject to controlled captive breeding programs in the hope of ensuring their survival. And experiments are being carried out to roll back the clock and reverse earlier extinctions by cloning. DNA from the remains of an extinct species is used to create a laboratory embryo that can be implanted into a similar host species; it was the stuff of fiction in Jurassic Park, but attempts to re-create the extinct Pyrenean ibex have already been made. Other target species are the Tasmanian tiger (Thylacinus cynocephalus), a relatively recent casualty, and the much more ancient woolly mammoth.
When: From about 1800 onwards
Death toll: It is estimated that in addition to countless species that have become extinct over time – many in recent centuries as a result of human activity or predation – one half of all species of life on earth will become extinct within the next 100 years if the destruction of Earth’s biosphere continues at its present rate.
You should know: One extinction that is almost guaranteed is that of the Geochelone abigdoni tortoise. There is just one left in the world – Lonesome George, the last remaining Galapagos giant tortoise of a species once found on the isolated island of Pinta. But many of 100-year-old George’s genes may live on as attempts have been made to mate him with a similar but different subspecies of tortoise and scientists hope that DNA will help them identify other pure-bred specimens on the neighboring island of Isabela. The quest to save his species has made George a potent conservation icon.