Dry Storeroom No. 1 (17 page)

Living lycopsids in New Zealand, showing a succession of vertical sporophytes, looking like little “brushes”

There is no danger of running out of new discoveries of fossils. I have been amazed by what has been prised from the rocks in China. As well as feathered dinosaurs and fossil flowers more ancient than any known previously, tiny fossilized embryos have been discovered in rocks still older than the Cambrian, the first direct evidence for animals in strata of this age. Seek hard enough, and finds shall be made; the book of the history of life must be continually rewritten. It could be argued that the recognition and naming of fossil species are less urgent than those of living animals and plants. They are not going anywhere from their sedimentary tombs—and, after all, most fossils belong to species already long extinct. This is to miss the point, for we are what history has made us. There are lessons to be drawn from the past extinctions and climatic crises that life has weathered—histories that may well equip us to cope better with the climate changes that are happening now. For example, the climatic warming of today marks a return to conditions on the “greenhouse earth” of mid-Tertiary times: suddenly the expertise of a palaeontologist who knows about this period will seem less arcane. Equally, the impoverished world that followed upon the great mass extinction at the end of the Permian period 248 million years ago provides a chilling prospect for humankind if we continue to degrade our planet in the way that we have been. This provides a pragmatic, sensible, utilitarian reason for studying the past, but one that is anthropocentric at root. I don’t want to reduce the fossil record to “lessons from history.” The real joy of discovery is to see the exuberance of life, those trilobites with tridents, or those great flying reptiles as big as gliders—organisms almost as exotic as the confabulations of Hieronymus Bosch, but thriving here on Earth long ago. To know about the wonderful excursions that life has taken is to be enriched, to be made aware of the fecundity of our small planet. This is what motivates palaeontologists to tap away for weeks on end at ungrateful rocks. This is the point of securing the booty recovered as testimony for generations of scientists to come in the drawers of the hidden museum.

4

Animalia

Zoology embraces all animals, not just the appealing furry or feathered varieties, so I will start with snails. Slugs and snails are regarded by some people as the least appealing of nature’s productions. As the nursery rhyme tells us, little boys are made of them, with added puppy dogs’ tails, to contrast with all that
sugar and spice and all things nice
that little girls are made of. But the Class Gastropoda is also one of the most diverse outside the insects and includes many miraculously beautiful coiled shells. One of the least spectacular, if most familiar, among the seashells are the little turreted winkles that one finds clustered on rocky shores. Sometimes they are found in such profusion as to make walking over the rocks a difficult business. Winkles are edible, although hard work. They are sold cooked in small tubs, and a traditional seaside delight was to “winkle” out the tough little morsels with a pin—hence the name of the pointy winklepicker shoes that enjoyed a brief heyday in the 1950s. A slightly more refined name for the little mollusc is periwinkle, but that is also the moniker of a plant, so I prefer the shorter version. David Reid in the Natural History Museum is devoted to winkles, and knows more about them than anyone. He is tall and thin, in early middle age, with a short, well-cared-for beard and glittering, intense eyes. David becomes extraordinarily animated when he talks about his favourite snails. He is to be found in the basement of the old building not far from the site of my first office. Almost all the other zoologists have moved to the new Darwin Centre, but the molluscs are still where they have always been. Such permanence is rather comforting, so when I visited David I could briefly imagine that I was still the young tyro strolling down the wide corridor with my life ahead of me. Winkles used to be placed in the single genus
Littorina,
the common (peri)winkle being
Littorina littorea,
which tells you all you need to know about its littoral—that is, shoreline—habitat. Nowadays, the winkles are divided into a number of different genera. “The great thing about them,” David enthuses, “is that you can collect them all over the world so easily. There is probably no better group to use to examine the relationship between geography and species.” Winkles do not run away when the scientist tries to catch them, they do not fall to pieces, nor do they have Threatened or Vulnerable status on conservation lists. Their flesh can be used to extract DNA readily enough. They are ideal subjects to winkle out the truth about evolution.

David Reid gathered together everything that was then known about
Littorina
in a huge monograph published by the Ray Society
^*7
in 1996, all 463 pages of it. The book is monumental. David tells me with characteristic self-deprecation that when it was published a Scandinavian colleague with less than perfect English wrote to him congratulating him on producing “a major millstone.” There must be hundreds of photographs of shells, and nearly as many of the radulae—the rasp-like “teeth” of molluscs—taken with the electron microscope, to say nothing of dozens of drawings of the penis, which is a critical character in winkles. There are details of the sculpture on the shells to help the reader identify a species in hand. It turns out that not only do winkles vary between species, but they also offer excellent examples of variation
within
species according to differences in habitat; winkles nestled among the barnacles will have different shells from those on more exposed rocks. In some localities there are a number of separate species on a single shore adapted to different heights above sea level. There are knobbly ones, ridged ones and nearly smooth ones. Some winkles have planktonic larvae, while others do not. In some species there is a good reason for a particular feature. For example, winkles living at high latitudes have the outer shell layer made of the form of calcium carbonate known as calcite, whereas the tropical ones tend to have the same layer made of its other form, aragonite. Calcite is less soluble in cold water than aragonite, so it makes sense to use this material in more arctic climates. Some species of winkle have to live on seaweeds; others refuse to do so. As more is learned it becomes clearer just why there are so many species of this lowly snail, and how they manage to coexist.

It might be thought that after the production of such a work there would be nothing more to be said. But David Reid believes that the truth about winkles is emerging only now that studies of molecular sequences have been added to the equation. In the last ten years he has been working with S. T. Williams on tropical winkles. The phylogenetic trees produced from the sequence data revealed that species from Australia and Africa were evolutionarily quite separate—so much so that they might be separated into different genera, called
Austrolittorina
and
Afrolittorina,
respectively, for obvious reasons. The most startling fact I learned about these two genera is that the nine species now recognized as belonging to them were formerly thought of as but a single, highly variable species. Furthermore, there are species of
Austrolittorina
and
Afrolittorina
that are completely indistinguishable on the shape and ornament of their shells. Yet their molecules tell us that they had separate evolutionary origins. The shells alone could not reveal this story. There could scarcely be a more powerful example of cryptic species—their recognition would have been impossible before the “molecular age.” The similar demands of shore habitats in their widely separated localities determined that the winkle shells evolved into an identically similar shape. The arrangement of the continents and islands that allowed the species to evolve in separation was itself a consequence of geological processes, as the tectonic plates carry on their unseen business, in this case, the separation of Australia from Africa as their respective plates bore them away. So geology, and evolution, and habitat combine to specify what a winkle should look like. The world is a lot richer than one might imagine. The apparently esoteric activity of studying marine snails tells us much about how this richness came to be. Consider the snail and be wise.

Sea shells can look very similar but have separate evolutionary origins: the “winkles”
Afrolittorina
and
Austrolittorina.

A little farther along the basement corridor, John Taylor still works in the same office he walked into in 1965; it retains the richly patinated hardwood cupboards with the names of molluscan families on the doors, so like those in my own first office. His office is a cramped space at the western end of the old building, with low ceilings revealing the iron skeleton of the Museum, beams and bolts and all. Visitors have to sidle alongside cabinets to get to the inner sanctum where the computer and the scientist reside. John retired some years ago, but continues to come into work almost every day. This might surprise some people for whom work has been an obligation and a chore, and for whom working for nothing might seem a strange concept, but then after forty years John Taylor is still as fascinated as ever by his clams—his work is simply who he is. Besides, there is always something new and exciting to discover. Just at the moment, he is researching into clams that harbour colourless sulphur bacteria in their tissues. These clams are specialists in the molluscan world: they actually cultivate the bacteria in their gills, and many species are adapted to absorb nutrients directly from the “plants” in their anatomical garden. John and his colleagues have shown that this adaptation is widespread in many different habitats: in mangrove swamps, or on seafloors low in oxygen, or around those strange, deep-sea sulphurous vents that exhale hot water along the mid-ocean ridges. The clams get food, and the bacteria grow in a protected environment—indeed, some clams have developed behaviours that help to “feed” the bacteria with the sulphur they require. Both parties benefit. It is a classic case of symbiosis. Some of these special clams can live in marine habitats that are very low in oxygen, which actually helps some bacteria thrive. It is a marvellous demonstration of the vigour of life to colonize even the most unpromising environments. And it is possible that such apparently obscure species will be important in coping with the polluted seas to which we humans are contributing. Taylor has proved that this specialist life habit has evolved no fewer than five times independently in the clams, but especially in a group called lucinoids. Once again, new evidence from DNA helps to prove this. It seems like any trick good enough to earn a livelihood in nature is good enough to be copied. And again we run into the taxonomic underpinning of the Museum, because John and Emily, his partner, have discovered a host of new species of symbiotic clams, even in places that have been sampled several times before. Some of them are tiny, and you could imagine how they would be overlooked. One or two are quite large, and one, from the California coast, is a really substantial fistful of an animal, which John first recognized from a museum collection. They need names, of course, and once described and christened will add another small turret to the edifice of biodiversity. That’s how enduring knowledge of the natural world grows: little by little with the help of enthusiasts.

It is not surprising that the rich attractions of the mollusc collection have made it the target of unscrupulous collectors. There is a kind of disease that afflicts certain naturalists that gives them an irresistible compulsion to own their objects of study as well as understand them. Sometimes this results in collections of lasting value to science—I have already mentioned a number of these coming as bequests to the Museum. In other cases the collecting compulsion takes a pathological turn—they
have
to own an example of a desired species, whatever it takes. The shell collector Tom Paine was one of these. As a trusted amateur expert he was allowed access to the collections for many years. Eventually, staff became worried by a series of disappearances from the drawers that seemed to follow upon his visits. These absences even included some of the precious type specimens—not the holotype maybe, but some of the other specimens that were part of the type collection. He could never be caught red-handed, but he was eventually excluded from access to the London collections. In the meantime he had apparently made similar light-fingered visits to other museums all around the world. After his death in the 1990s he bequeathed a magnificent and enormous collection to the National Museum of Wales, but the origin of many of the specimens will probably never be sorted out. An even more blatant example was another visitor who raided the birds’ eggs. This is one of the more familiar obsessions, and one that I can understand, because as a young boy, before it became illegal, I briefly collected eggs myself, as had my countryman father before me. I am ashamed of it now, but I can recall the excitement of coming across an uncommon species; and birds’ eggs are fragile and beautiful objects. They are just the kind of thing to attract an oddball kleptomaniac. This particular thief appeared in a wheelchair; he secreted the desired birds’ eggs inside women’s tights that he then tucked into his trousers before making good his exit. He was discovered and prosecuted. It later transpired that the reason he was in a wheelchair in the first place was that he had had an accident stealing copper from electrical installations. Shells, eggs, fossils—it matters not—all intrusions into the collections are taken very seriously, and have to be reported to the Trustees by the Keeper of the department concerned.

One of John Taylor’s discoveries in Western Australia, which was named by him and Glover in 1997; a lucinid clam
Rasta thiophila
(thiophila means “sulphur lover”)