Humans have been classifying life for as long as there have been humans. Since the mid-1700s, we have employed a standardized nested nomenclature for defining what is same and what is different: the word "species" denotes things that are the same-same, and the word "genus" groups things that are same-ish. Genera that are almost-but-not-quite the same are lumped together in the same "family", similar families are assigned to the same "order", and so forth. Today, the scientific interpretation of sameness is based on what we know about evolutionary history, such that assignations to species, genus, etc., reflect the degree of relatedness between two lineages. And our ability to sequence DNA enables us to determine just how related two organisms really are.
As biologists work at piecing together this story of life on earth, their minds continually drift to Major Unresolved Issues, which is an important-sounding way of saying "Impossible questions that your six-year-old daughter would ask you during a trip to the museum". For example, "How many species are there in the whole wide world?"
Reasonable question, and biologists have tried hard to come up with a reasonable answer. The most recent attempt was published recently in PLoS Biology, and estimated that the number was 8.7 million, plus or minus 1.3 million, for an upper bound of 10 million.
Such estimates beg another question, this one asked not by your six-year-old daughter, but by her annoying little friend: "Who cares how many?" The answer is that some people do, and some people don't. One argument in favor of caring was presented by Bob May in a short essay published alongside the recent PLoS Biology piece. May considers the new estimate plausible and argues that "if we are to meet the challenges facing tomorrow's world, we need a clearer understanding of how many species there are ... underpinning the structure and functioning of ecosystems." A contrasting and thought-provoking perspective is offered by University of Pennsylvania biologist Dan Janzen, and I publish it here with Dan's permission.
Ten million species? The real number is easily double that, since DNA barcoding is showing us that something like a third to a half of the species that we think are one species are actually two-or-more species that merely look (or act, smell, bite, taste) like the same thing. There are six species of giraffes, three species of orcas, and two species of African elephants. The list goes on and on and on and on. Who cares? Look at a pasture filled with burros, horses, zebras and quaggas, and tell me when the usable description is "grass dotted with equines". Malaria is carried by particular species of mosquitoes, not "mosquitoes".
People love metrics. They are so proud of their fingers that they have to count any time they can. But tallying the number of species is really, truly a waste of time -- an absurd thing to measure in most cases. It matters not a bit whether a tropical forest just cut down contained 100,000 species or 150,000 species or 300,000 species. The loss to humanity is that all those species gave us the ability to smell, see, think, feel, itch, wonder, hear and puzzle over. They moved us from primeval to the Homo sapiens we know and are; and we are busily trashing them off the planet, taking away the very things that fashioned us into being, knowing, feeling, and seeing that we are in something other than a dull white box. Humanity deserves more than alfalfa, parking lots, and comic books.
The species loss, and the loss of their interactions even more so, is not a tragedy because we cannot count them. It is a tragedy because they are gone, quite irrespective of whether there were 1 million, 10 million, or 30 million. And if you knew that there were at this moment, 27,538,258 species on planet Earth how would that help anything, anywhere, anytime? Not one bit. Turning it upside down, in order to save a significant block of species and all the wonderful (and painful) things that they do to and with each other and us, I do not need to know whether that forest contains 100,000 of them or 1,000,000 of them, or any number in between. What I need to know is what they do, how to tell one from another, where they are, and how to get a particular one to hand or eye at the moment that it happens to matter to me or to you. And what we all need to do is to get that information back into our hands and minds at the time you want it. In return, there just might be some chance of having some serious portion of that wild biodiversity (again) be welcome to at least some serious portion of society. In the face of ravenous Homo sapiens multiplying even faster than the proverbial rabbits, there is no other hope.
Please save us from the very human tendency to, in our frustration of watching and feeling our very own ancestral mold melt away, turn to counting. When the house is burning, you do not need a enumerated thermometer, you need a Fire Department.
Dan Janzen, Department of Biology, University of Pennsylvania, 11 September 2011