The Tree (6 page)

I can’t resist one last example. The British tend to feel that cedars are conifers of the genus
Cedrus,
relatives of the pines in the family Pinaceae. But in America a whole range of lovely trees are called “cedar,” including various members of
Calocedrus, Thuja, Chamaecyparis,
and especially
Juniperus,
from the Cupressaceae, the family of the cypresses and junipers. West Indian cedar is
Cedrela,
from the Meliaceae, another relative of mahogany. Thus the common names may flit not only from family to family but also leap the enormous gulf between conifers and broadleaves.

THE PROS AND CONS OF LATIN AND GREEK

The formal scientific names of living creatures are often called “Latin.” There is truth in this. The medieval naturalists who laid the foundations of modern nomenclature were classical scholars first—and we should be grateful that they were: the formal names can seem very long, but they have an elegance that would be difficult to achieve in most languages. Of course, though, they are not strictly Latin. They are compounded primarily of Latin plus Greek, but in their modern forms they also incorporate bits of scores of other languages, from Swahili to Inuit, plus the names of people and places, as in
Taiwania
and
cunninghamii.
Above all, the “Latin” names are consistent. Each name is mooted by whoever first describes the creature in question, and then must be approved by committees of specialist taxonomists, who decide what is appropriate.

Even so, there are snags.

First, in recent years the specialist taxonomists who look after plants decided to rename many of the families. In the old days, most plant families ended with the suffix “-aceae,” as in Fagaceae (the family of the oaks and beeches) and Betulaceae (the family of the birches). But some plant families, for historical reasons, had different endings, as in Leguminosae (the pea, bean, laburnum, and acacia family) and Compositae (the family of daisies and thistles). But a few years ago the powers that be decreed that
all
plant families must end in “-aceae,” and so the ones that didn’t were renamed. The Leguminosae became Fabaceae. Compositae became Asteraceae. Palmae, the palms, became Arecaceae. Gramineae, the grasses, became Poaceae. Labiatae, the family of mint, basil, and some surprising trees (which in the interests of suspense I will discuss later) became Lamiaceae. The family of carrots and celery, traditionally known as the Umbelliferae, after its umbrella-shaped inflorescences, became the Apiaceae. (Incidentally, “-aceae” should be pronounced with all three syllables:
ace-ee-ee.
)

Second, as briefly explained in this chapter and as will become apparent in Part II, taxonomy as a whole (the craft and science of classification) has upped its game of late. New techniques have come on board: notably, the discipline of cladistics; direct investigation of DNA; and the use of the computer, which has vastly increased the amount of data that taxonomists are now able to take account of. These new techniques have given rise to a flurry of reclassification in recent years as older ideas, based mostly on the skill and experience of specialist individuals, have succumbed to new rigor. Worse: when DNA studies first became possible in the 1970s, biologists tended to assume that they would provide the royal road to truth. In reality, those studies have caused at least as much controversy as the traditional classifications did.

Perhaps (with luck) the worst of the turmoil is over. The new classification, based on the new techniques, is beginning to settle down. Even so, there is still a lot of shuffling. Many species are still being transferred from family to family. Some families are currently being split into more than one, and others are being fused. All of this to-ing and fro-ing is liable to entail some name changes.

Finally, the Latin names can be rather long, and sometimes too similar for comfort. If you’re sitting up late with a 40-watt bulb it’s easy to confuse, say, the Myrtaceae, Myricaceae, Myrsinaceae, and Myrsticaceae. But then, many languages that people use every day are enormously polysyllabic—like German and some of those of Sri Lanka. Gardeners love to dazzle their employers with polysyllables, and small children revel in the names of European football teams and dinosaurs. If you can say Mönchengladbach and
Tyrannosaurus rex,
you can say
Sequoiadendron.
The only trouble is that at present you cannot be sure that
Sequoiadendron
will still be called
Sequoiadendron
in ten years’ time. But it probably will. Though the Latin names have their drawbacks, they are worth it, and we should be grateful to the old-time biologists who first began to put them in place.

Naming, however, is only the first step. Classification requires another order of endeavor.

GETTING SORTED

Classification at its most basic is an exercise in convenience; and if convenience is all we are interested in, then any of us is free to carve up the world as we choose. So it is that fishmongers and chefs recognize the category of “shellfish,” which includes anything that lives in water and is crunchy on the outside and soft on the inside—in practice, an astonishingly mixed bag of crustaceans (such as shrimps and crabs) and mollusks (such as whelks and oysters). Timber merchants label all conifers “softwoods” and all broad-leaved trees “hardwoods.” They do this even though some conifers are a lot harder than many hardwoods, and the softest woods of all are in truth “hardwoods.”

But there seems to be an innate order in nature; and at least some—perhaps most—of the terms by which most peoples classify living things do seem to reflect that underlying order, something more than mere convenience. Thus in English as surely in most languages we recognize the category of “insect” and on the whole take “insect” to be different from “spider.” “Birds,” “horses,” “dogs,” and, indeed, “conifers” and “flowers” (meaning flowering plants) are vernacular categories but, again (unlike “shellfish”), they do seem to reflect some real quality of nature: a true orderliness. In short, deep in the human psyche (and deep in the psyche of animals, too, as can be shown in laboratory trials) is the belief that nature
is
orderly, at least to some extent. Behind the terms “robin,” “duck,” “eagle,” and “canary” lies, very clearly, the broad general concept of “bird.”

This simple musing raises a series of deep questions—deep enough to have kept philosophers and biologists occupied for thousands of years. First, is the order that we think we perceive “real”? Intuitively it seems obvious that shrimps and oysters are very different, even if they are lumped together as “shellfish,” while ducks and robins really are variations on a single theme that we might as well label “bird.” But can we trust our intuition? Might it not be that all creatures are entirely independent of one another, and that ducks in reality are no more similar to robins than shrimps are to oysters? Intuition tells us that there is indeed order; but we know that our intuitions can be wrong.

Second, if the order is “real,” not just a trick of our minds, how do we pin it down? Insects, for instance, are immensely various, so why do we call them all “insects”? By what criteria do we place butterflies and beetles and grasshoppers in the same grand category, which we take to be different from the grand category of spiders? Are those criteria valid?

Then, third, there’s the issue that has especially exercised theologians (and a great many biologists) over the past two hundred years:
why
should nature be orderly? Where does the order come from? Is it orderly simply because it is the creation of God (as Genesis tells us), and God has a tidy mind? Or are there other feasible or indeed necessary explanations?

If
the order in nature is “real,”
if
it reflects some deeper underlying intent or force, then it would (would it not?) be very good to reflect this in the classification. A classification based purely on convenience (shellfish, softwood, hardwood) is just a temporary device, a throwaway thing, that meets the needs of particular trades at particular times. A classification that reflects the true order of nature—a “natural” classification—provides true insight: insight, so many philosophers have opined, into the mind of God; or insight, so others have insisted, into forces that have brought order into being, whether inspired by God or not. Thus, the idea of providing a truly “natural” classification has engaged philosophers since, well, at least since the beginnings of philosophy.

Plato and his pupil Aristotle are commonly taken as the twin founders of modern Western philosophy, and they had different ideas about where “order” comes from—and both ideas have been reflected in the attempts of later biologists to provide a natural classification. Thus Plato thought that everything on earth is merely a copy, and a flawed one at that, of some “ideal” counterpart that exists in what might be called “heaven.” These ideals were in fact more “real” than the things we see around us. Plato’s ideas were absorbed into Christianity, and Christianity has been a driving force in Western science, so biologists until well into the twentieth century were wont to think, Platonically, that all earthly things and creatures are ideas of God. Thus in the late nineteenth century Louis Agassiz, then an extremely influential professor of biology at Harvard, declared that each separate species is a “thought of God.”

Aristotle was on the whole more down-to-earth and rejected Plato’s “ideals.” Instead he spoke of “essence”: there is no ideal insect, of which beetles and butterflies are reflections; what we see is what there is. Nonetheless, all insects share some “essence” of insecthood. Aristotle, unlike Plato, was a naturalist; he liked to look at nature. And he was the first philosopher that we know about who tried to devise a “natural” classification that truly reflected the essences of different forms. In doing so, he set out the most basic rules of taxonomy—and identified some of the key problems. Thus, he said, if we really want to see who belongs with whom, then we have to see what features they have in common. More specifically, the taxonomist must pick out particular “characters” (the biologist’s term for “characteristics”) of each of the creatures in question, and then see which and how many of those characters they share with other creatures.

This is fine as far as it goes. Feathers are a very clear character of birds, and all living creatures with feathers may reasonably be classed as birds. But what about, say, number of legs? That is a clear character, too. But birds have two legs, and so do humans. Do birds and people belong together? Everything else about humans seems to suggest that we are closer to dogs, monkeys, and other mammals: like them we have hair rather than feathers, and we produce live babies rather than eggs, and women suckle their babies as other female mammals do and birds do not. So what do we make of our two-leggedness? Well, the broad generalization is that in seeking the true order of nature, some characters are more informative, or less deceptive, than others. Feathers are a good guide. Number of legs is a less good guide. Or at least this is true in this instance. When it comes to telling insects from spiders, the number of legs is a very good guide indeed.

From the time of Aristotle, and with many a diversion, the art and craft of taxonomy shuffled along, as naturalists and apothecaries, and anyone else with an interest in nature, tried to classify the creatures they dealt with, and to some extent at least tried to create systems of classification that were “natural” and reflected the true order of nature. The medieval herbalists made great progress, describing an impressive variety of plants, with Latin (or Latinesque) descriptions to match. In the Middle Ages emerged the idea that different species of similar plants could be grouped together into genera (singular: “genus”), and this thinking is reflected in the names they gave to their plants. They did not have enough data; communications were not good, and they tended to work semi-independently; and they had few robust principles to guide their thinking. But they did a lot of vital groundwork nonetheless.

The seventeenth century saw the birth of recognizably modern science, both in method and philosophy. The method included close, repeatable, quantified observation and orderly experiment. The philosophy included the final acknowledgment of the idea that the universe is indeed orderly. It was run, so Galileo and Newton and other great seventeenth-century physicists averred, according to natural “laws,” an idea that is still with us, at the heart of science. Naturalists quickly got in on the act. Living creatures are far more various in form and in their behavior than are the planets, or the mechanical devices that the physicists and engineers played around with. But even so, the naturalists felt, biology should have its “laws” too. This general feeling reinforced the idea that the apparent orderliness of nature, which is reflected in general terms like “bird” and “insect,” did indeed have deep origins.

John Ray was outstanding among the seventeenth-century naturalists who sought to broaden the scope of classification, to include many more creatures than the herbalists had, and to devise ground rules for finding the true order of nature that lies behind appearances. Notably, in our present context, he distinguished two great categories of flowering plants—a distinction that still persists. Some flowering plants, he pointed out, have long, narrow leaves, like lilies and grasses; others have broad leaves. More than a century later the French taxonomist Antoine-Laurent de Jussieu pinned down the deep difference that lies behind this distinction. The embryos of all flowering plants, still within their seeds, have leaves, known as “cotyledons.” The embryos of narrow-leaved flowering plants, such as lilies, grasses, and palm trees, have only one cotyledon. The embryos of broad-leaved plants, like oak trees and daisies, have two cotyledons. Hence the two great groups of flowering plants: monocots and dicots (much more of this in Chapter 6). Jussieu’s discovery illustrates another great principle, in line with Aristotle’s musing over the number of legs: that the characters that really count, and really show who is related to whom, are often ones that are
not
particularly obvious; indeed, they are “cryptic.”