Charles Darwin showed that extinction of a species is part of the evolutionary process. There is no reason at all to be concerned about a vanishing species. In fact, a steady rate of extinction is a normal process in the course of evolution, and is called the background rate of extinction. Species have always evolved and disappeared throughout geologic time because of climatic changes and the inability to adapt to survive competition and predation.
The Dodo Bird
A lesson in extinction. First sighted around 1600 on Mauritius, an island in the Indian Ocean, the Dodo was extinct less than eighty years later due to the influx of sailors, who destroyed their natural habitat, the forest.
But in making this argument, one very important fact is overlooked: since the 1600s, humans have rapidly accelerated the rate of extinction because of population growth and resource consumption. Today, most of the world's habitats are changing faster than most species can evolve or adapt to such changes. The current global extinction rate is estimated at about 20,000 species per year, many times greater than the background extinction rate. Many biologists believe that we are in the middle of the greatest mass extinction episode since the disappearance of the dinosaurs 65 million years ago.
From what is known about present-day populations and from evolutionary theory, the change in either the physical or the biological environment is the key to extinction. But vulnerability also depends on many factors, such as its total population size, geographical distribution, reproductive ability, ecological relations with other species, and genetic characteristics. For example, there is more concern for species that reproduce slowly as opposed with those that reproduce rapidly. Other factors, such as food availability, may make even fast reproducers more endangered than slowly-reproducing species. It does not matter how fast a certain species can reproduce if its food source dies out first.
It has been estimated that, in all of earth's history, 0.5 billion species have lived. Those species that live today are only 2% of those that have ever evolved. The other 98% have died out or evolved into new species.