Scientists name about 18,000 new species each year. This colorful tarantula, Typhochlaena costae, was recently discovered in Brazil.

In recent years, newfound species have included brilliant blue tarantulas from Brazil, a polka-dotted Pacific Oceannudibranch, and a pink, spiny millipede from Thailand. And who would not coo over a chubby, lumbering Peruvianwater bear or a translucent green glass frog from Ecuador? (See "An Ode to the Odd and Obscure.")

I understand the appeal of species like birds and primates that, with beautiful plumage or similarities to ourselves, are relatively well known and attractive. What's more, discoveries of new species in these groups are increasingly rare events.

But the simple fact is that no two species are alike, and each has something unique to teach us about ecology or evolution.

Largely ignored by popular media, scientists name about 18,000 new species each year, and the nearly two million species named since the 1750s have only begun to reveal the biological diversity of our most remarkable planet. (Read "Building the Ark" in National Geographicmagazine.)

That's because scientists predict as many as ten million kinds of plants and animals await discovery, and that does not take into account the microbial world, which may well be even more diverse.

Now or Never: Count Our Species

Biodiversity is threatened on a scale never before witnessed by humans. By some estimates, species are going extinct a thousand times more rapidly than in recent geologic time, while the pace of species discovery is unchanged since the 1940s.

Unabated, the current rate of species extinction could lead within three centuries to the first mass extinction event on our planet in 65 million years and a loss of 75 percent of all species alive today.

A prudent first step would be to complete an inventory of species. Stated bluntly, if we do not know what kinds of plants and animals exist or where they live, how are we to detect invasions by foreign species, losses of species from ecosystems, or shifts in distributions due to climate change? Ignorant of more than 80 percent of the flora and fauna, we are flying blind into an unprecedented storm of extinction. (See "Pictures: Pygmy Sloth Among 100 Species Most at Risk [2012].")

While a comprehensive plant-and-animal inventory was only a dream a generation ago, it's now within reach. Technological advances ranging from DNA analysis to cyber infrastructure, combined with coordinated teamwork and a growing rank of citizen scientists, make a preliminary inventory possible within decades.

It's been estimated that such a large-scale taxonomic project would cost a billion dollars annually over 50 years.

That's a large sum compared to current expenditures on species exploration, but it's a bargain by other measures. Consider that the U.S. alone currently spends more than $130 billion per year dealing with invasive species.

The investment would be handsomely rewarded in at least three ways. I have already mentioned the obvious importance to ecology and conservation of creating baseline knowledge of what species exist to begin with and where they are found. To this we may add evidence of our origins and better access to species for biomimicry, a scientific field that uses nature to solve human problems.

For instance, every feature that we conceive of as uniquely human is modified from something in our early ancestors. Their characteristics, in turn, are traceable to even earlier mammals and so on, all the way back to the first living species. The story of our origins is told through details of evolutionary history only knowable through comparative studies of as many species as possible.

In order to find the most sustainable ways of meeting human needs, then, the ideal approach would be to spend thousands of years conducting every trial-and-error experiment we could imagine, stockpiling a massive number of alternatives and choosing among the very best to adapt to the world around us as it changes.

But natural selection has done the job for us. Working without rest for more than three-and-a-half billion years, it has created a lab notebook filled with billions of solutions to as many problems. We can learn these lessons by exploring and describing species, a process greatly enhanced by pausing to marvel at these discoveries as they happen.

Golden Age of Species Exploration

No future generation will ever have the opportunities that we do to explore the results—all 12 million of them—of billions of years of evolution. Earlier generations of taxonomists lacked the travel, communication, and data management tools to complete an inventory of life on a planetary scale, and future generations will live in a world in which much of the living diversity is gone. By expanding efforts to discover species and preserve evidence of them in museums, we hedge our bets against future losses. (See National Geographic's pictures of rare species.)

The more we learn about species, the more we will understand about our origins and the better prepared we will be to successfully sustain biodiversity in enough abundance to ensure that Earth's ecosystems are resilient to change and meet human needs.

If we play our cards right, the 21st century will be remembered as the golden age of species exploration. Citizen and professional scientists working together, combined with coordinated international inventories and strategic investments in infrastructure, can ensure that we preserve as much biological diversity as possible and at least some knowledge of the rest.

Discoveries of Earth-like planets increase the probability that life exists elsewhere, but their vast distances from our solar system are reminders that Earth may well be the one and only planet on which we can study the intricacies of evolutionary history and biosphere organization