Species that are unable to survive or reproduce in their environment and an alternative environment is not available, will become extinct.

On the long geological time scale, extinction is not an unusual event, and several mass extinctions due to cataclysmic events, such as meteors, wiped out the majority of species alive at the time. Or extinction of a species may occur gradually over thousands or millions of years, as when another species better suited to the environment out-competes the previous species for resources.

It is true that over the course of evolution, in the last 3 billion years or so, most species of organisms that developed eventually died out. This means that all the life on earth today comes from only 1% of all the life that every existed!

Even though evolution is a constant process, and most species have died over the history of living organisms, the extinction events caused by human behavior is particularly astounding. Human technology has developed very quickly, with farming beginning less than 10,000 years ago. Humans have had a much more global and wide-ranging effect on all ecosystems than other organisms prior to us, and this means that the extinction of other species has sped up as well. Human development and population growth has eliminated many habitats for plants and animals, and environmental pollution and introduction of non-native species has also sped the rate of extinction to hundreds of times higher than before human influence. There are several reasons why effort should be made to conserve species, and to slow the current rate of extinction.

The effects of accelerated extinction are seen not just in the loss of the species, but also in the effect on the whole ecosystem. Each organism is linked to many others in a delicate balance within the ecosystem, and removal of one species may disrupt many more.

There is an economical benefit to a diversity of species, humans can use biodiversity for food and industry, tourism and recreation, and scientists have even found sources of medication from different species. If plants and animals go extinct before they have been discovered and studied, or just continue to perish, humans will lose these benefits too. Finally, there are more abstract reasons to conserve species, with some believing that it is morally wrong to voluntarily cause extinction, and with biodiversity playing a central role in some people's spiritual heritage.

So, though extinction is a natural part of evolution, it is occurring at unnatural rates due to human impact, and it will be beneficial and essential for the future to conserve species now.