Species extinction is a natural part of the evolutionary process. Due to human activities, however, species and ecosystems are more threatened today than ever before in recorded history. The losses are taking place in tropical forests -- where 50 - 90 per cent of identified species live -- as well as in rivers and lakes, deserts and temperate forests, and on mountains and islands. The most recent estimates predict that, at current rates of deforestation, some two to eight per cent of the Earth's species will disappear over the next 25 years. While these extinctions are an environmental tragedy, they also have profound implications for economic and social development. At least 40 per cent of the world's economy and 80 per cent of the needs of the poor are derived from biological resources. In addition, the richer the diversity of life, the greater the opportunity for medical discoveries, economic development, and adaptive responses to such new challenges as climate change. The variety of life is our insurance policy. Our own lives and livelihood depend on it.
In 2001, paleontologists reported that evolution does not accelerate quickly in response to rapid bursts of extinction, and that the Earth needs, on average, about 10 million years to recover from global extinctions, whether they involve the loss of most life on Earth or wipe out far fewer species. This is much longer than previously believed. One possible explanation for why diversification takes so long to speed up after an extinction is that extinction eliminates not merely species or groups of species, but removes ecological niches: the roles which organisms play within ecosystems. Recovery becomes more complicated because specialized roles, such as parasites that live on just one species, or animals that consume just one kind of food, do not evolve until their hosts are already well established.
2. Extinction is not like knocking chess pieces off a chessboard, with the empty squares ready for you to plunk down new pieces. Extinction is more like knocking down a house of cards. You only have places to put new cards as you rebuild the structure of the house.