99.9% of All Species Have Already Gone Extinct
From The Economist: "More species are under threat than ever before according to the World Conservation Union (see chart above). Its “Red List” gives warning that 16,306 species are now under threat of extinction, nearly 200 more than in 2005. This number has risen steadily since the first report in 1996."
Before you get too concerned, consider this: "Since life first appeared on Earth some 3.8 billion years ago, it has been estimated that more than 99.9% of all species have gone extinct. Billions of species have gone extinct throughout geologic history. Many of these went extinct during mass extinction events, the most famous and well documented of which took place some sixty-four million years ago at the end of the Mesozoic Era. This mass extinction event marked the end of the reign of dinosaurs."
And consider this from The Economist: "Nobody knows how many species occupy the planet. Most experts think 10 million is roughly correct, though they have only formally noted 1.4 million."
Suppose that half of the 16,000 threatened species went extinct, a highly, highly unlikely event. That would be less than a 1/10 of 1% extinction rate, meaning that more than 99.9% of all existing species would surve.
Question 1: Wouldn't a 0% extinction rate (100% survival rate) be undesirable because it would be too costly?
Question 2: Isn't is true that the optimal number of extinct species is probably NOT zero, assuming that it is costly to save some species; just like the optimal amount of pollution is NOT zero, the optimal amount of traffics deaths is NOT zero, etc.?
I would say Yes to both. Like all other decisions, we need to weigh the costs and the benefits.