Biologists share a conundrum with astronomers these days. Most of what they study exists in forms they cannot see. For astronomers, it's an unknown substance they call dark matter, which nevertheless represents the bulk of cosmic material. For biologists, it's the microbes that swarm all over our planet.
Many known microbes haven't yet had any scrutiny. Also, microbiologists say they are convinced that many species remain undiscovered. Thus, when it comes to life on Earth, the majority of its organisms are as invisible for practical purposes as the astronomers' dark matter.
Sean Nee at the University of Edinburgh calls this the scandal behind the worldwide concern for biodiversity.
Ecologists rightly warn that we are losing species rapidly, Dr. Nee notes. Measures taken to slow that loss are important.
Yet these measures deal only with the visible world of higher plants and animals. In a commentary in Nature, he chides ecologists for talking about biodiversity without considering the invisible microbial world, which has far more diversity and many more species than what we see around us.
The latest twist in an ongoing puzzle illustrates the point.
Some biologists speculate that bacteria far smaller than any now known may exist. In 1998, Olavi Kajander and Neva Ciftcioglu at Finland's University of Kuopio claimed to find one. The evidence was weak. Critics discounted the claim.
Recently, John Lieske and colleagues at the Mayo Clinic in Rochester, Minn., reported that a four-year study of the suspect particles has produced "suggestive" evidence that they may be alive. They replicate themselves and appear to have DNA.
This is not solid proof. Particles may be only lifeless crystals, as critics maintain. Yet many skeptics said the same thing about virus particles 60 years ago. Now viruses are recognized as the most abundant life form on the planet.
There also is diversity in basic life processes. Take breathing for example.
Plants incorporate solar energy into food. Both plants and animals then "burn" that food with oxygen to release the energy for their life processes. Microbes are more diverse. Some "breathe" metals to sustain their lives. Some burn ammonia with nitrate.
Visible life depends on sunlight as its ultimate energy source. Many microbes can use the energy of inorganic chemicals instead.
Trying to understand earthly life without taking account of the invisible microbial world - poorly understood though it may be - is like trying to understand the stellar universe without taking account of equally inscrutable dark matter, which exerts dramatic gravitational pull throughout the universe.
Astronomers know better and are doing all they can to improve their knowledge. Nee urges life scientists to do likewise.
He says they should drop the bias that focuses largely on visible life and include the microbes to the fullest extent possible in their efforts to understand how the world's ecosystems actually work.