June 6, 2012 7:27:34 AM
Creationists who think themselves clever sometimes spout this argument: "If evolution is true, and humans came from monkeys, then why are there still monkeys?" There is just too much wrong in this question for an easy science-oriented response. The creationist who wanted to come closer to asking an intelligent question might think of asking, "If evolution is true, then why are there still horseshoe crabs?" After all, horseshoe crabs have hung around and look about the same as their fossils from 450 million years ago (of course, a strict reading of the Bible precludes any such age); if evolution has been at work, where are their changes? Richard Fortey has the answer in Horseshoe Crabs and Velvet Worms: The Story of the Animals and Plants That Time Has Left Behind (Knopf). He seems to have a special affection for horseshoe crabs because they have some similarities to the trilobites that were the focus of his paleontological research (and about which he wrote in Trilobite! Eyewitness to Evolution). However, less well-known animals like velvet worms are here, and mounds of stromatolites (formed by blue-green bacteria), sponges, ginkgoes, lungfish, lampreys, platypuses, cockroaches, and many more. Fortey has tried to get to see most of these animals in their natural habitat, so the book is a bit of a travelogue, too, brightly written with genuine affection for his fellow researchers and for the animals he gets to see.
This time the paleontologist is writing about living creatures rather than fossilized ones. These animals are often called "living fossils," with an appreciation of just how contradictory such a paired-word term is. Fortey explains at the beginning that it is a colorful oxymoron, but misleading. For instance, current horseshoe crabs are not identical to the fossil varieties, although the similarities are easy to see while the differences require true expertise. There have been changes; no creatures survive for millions of years unchanged. The ancient DNA would be considerably different (if we could find it) from the current DNA, even though the differences do not show up in the appearance of the organism. The ancients certainly do not occupy the same ecological niche as the present ones; for instance, when there were first horseshoe crabs, there were no birds to feed upon their eggs, but the eggs are an important feast for birds now. There is, however, a special significance in these specimens: "What can be said without demur is that the ancient survivor and its other living - and more evolutionarily advanced - relatives will have shared a common ancestor, and that the features of the living fossil will be close to those of the ancestor. The discovery of ancient fossils more or less similar to the survivor will date the appearance of the whole animal group to which they belong, and point up the changes that must have happened through geological time along the subsequent branches of the evolutionary tree." It is this sort of descent that Fortey repeatedly traces in these remarkable creatures.
Fortey starts with an orgy on the Delaware beach (that ought to pull in the readers). He went to see the nocturnal spring mating rituals of thousands of gathered horseshoe crabs "with my notebook and a fluttering heart." It is hard not to share his enthusiasm in this and his other expeditions. Readers will learn plenty about each animal visited. The horseshoe crabs are not really crabs, but like his beloved trilobites, are a different sort of arthropod. He notes that to call the horseshoes living fossils seems to be insulting them, "as if the poor old organism was just about tottering along on its last legs." The animals described in these pages are healthy individuals, although indeed many of the species have populations threatened by human encroachment. Here is a public service announcement for biological research that might otherwise be ridiculed, and a good use of taxpayer money for it: there is a component of horseshoe crab blood that can detect minute quantities of bacterial poisons. Ironically, this put the survival of the horseshoes at risk from the pharmaceutical companies, as they had been from fertilizer companies the years before. (This is far from a fretful book, but Fortey often digresses about realistic concerns that the species he describes, having lasted so many millions of years with minimal changes, will succumb to the great die-off brought about by our own most invasive species muscling in everywhere.) As Fortey describes each of these survivors, he gives a short course in their particular biology. For horseshoe crabs, the most interesting part of their physiology is that they are literal bluebloods. Their blood is not based, as that of us mammals, on iron, but on copper. Also, they have a diffuse circulatory system compared to ours, with the blood sloshing around rather than being directed by arteries and capillaries. Going along with this system is a fast means of clotting, sealing off any injuries or infections. It is an admirable system (and is what makes the horseshoe's blood an indicator for bacteria in the lab), and it is part of what has helped this strange beast survive. Throughout this book, Fortey's tone is one of admiration, and he communicates it well. Looking at an inverted horseshoe crab, he notes the pincers at the ends of its feet: "I am reminded of the manual toolkit owned by the eponymous hero of the movie 'Edward Scissorhands.'"
Fortey's worldwide rambles have allowed him to reflect on just how these particular species survived so long without changing. He recalls with amusement that when a member of a community reaches a hundredth birthday, the local media will make a story of it, and the subject will be asked how such longevity had been achieved. One centenarian will claim it is avoiding strong drink, another will say it is enjoying a nip now and then, another will say it's a life of hard work, another will say it is religious faith, and so on. (My favorite reply: "I don't rightly know, but I can tell you if I had known I was going to live so long, I sure would have taken better care of myself.") "In general," says Fortey, "it is difficult to talk about survivorship except in terms of human virtues." The oldsters will seldom credit the randomness of good genes and the general randomness of life. In the oldster species he gives us here, they can't claim any virtuousness, but mere happenstance. Somehow Fortey's dear trilobites all died out, perhaps because of lack of oxygen 250 million years ago, and maybe, by chance, the horseshoe crabs had an affinity for shallower waters with more oxygen when the change took place. If horseshoe crabs had any sense, they would bless their good fortune that they made it through. We, whose forebears were of course struggling along in their own way at the time, changed instead of keeping our old forms, and if horseshoe crabs can't be grateful for the particular way they bumbled though, we ought to be grateful for our own.
Fortey is a wise and amiable companion on this tour. He comes home and finds that there has been an invasion of cockroaches, and while he might be disgusted, he can't refrain again from admiration ("they must earn a grudging respect for their durability and lack of fussiness"). Cockroaches are survivors, with some of the characteristics of other species included here; they are relatively long lived and they can go for long periods without nutrition. They scurry away fast when light hits them, but they are otherwise sedentary; as he writes when describing the lungfish, "As an American might say, they take life real slow." Even when writing about cockroaches, Fortey writes in summary, "It has been a privilege to get to know every animal and plant in this book." It's the sort of scientific affection that comes through on every page. It will be hard for any reader not to feel it, nor to feel affection for this friendly and broadly informed tour guide.
4. A Stone's Throw: Beware COLUMNS