Eight Little Piggies (43 page)

Agassiz used
Cephalaspis
as a primary illustration of his embryological vision for geological history. As a representative of the oldest fishes,
Cephalaspis
fulfilled all expectations for a primordial creature in Agassiz’s vision of differentiation as the guiding principle of history. Agassiz located two different supports for his theory of differentiation in “the bizarre characters of this genus” (
les caractères bizarres de ce genre
). First, he viewed the single solid head shield (not divided into separate cranial bones linked by sutures) and the few, simple scales covering the body as marks of a primitive generality—a source for later differentiation of separate bones and more complex scales. Second, he twisted to his advantage the old bugbear of superficial resemblance between the shield of
Cephalaspis
and the head of trilobites—for this similarity indicated that the major trunks of animal life did draw closer to a common simplicity at life’s source.

Finally, Agassiz delighted in the great age of
Cephalaspis
, for its antiquity proved that all four trunks lived simultaneously at the dawn of life. The most complex group of vertebrates did not arise later as a possible evolutionary descendant (heaven forfend) of a simpler trunk.

Agassiz’s theory of a God ordering his creation by embryological rules of differentiation was clearly not an interpretation logically entailed by objective facts of nature. It was a vision rooted in a cultural context still unable to embrace evolution, and in the personal psychology of Agassiz’s own interests and training. Agassiz imposed his theory upon
Cephalaspis
and highlighted only those facts most congenial with his preferred views. Yet his use of
Cephalaspis
cannot be read as a vindication of relativism. Agassiz may have exploited
Cephalaspis
in the interests of his vision, but he also unearthed the primary fact that fueled all later discussion. He proved that
Cephalaspis
was a vertebrate by discovering the body of a fish behind a head shield that had confused all earlier observers.

When William Patten used
Cephalaspis
as the centerpiece of an important theory eighty years later, the context of science had changed irrevocably. Evolution had triumphed, and
Cephalaspis
would now be invoked in the interest of genealogical claims. Our cardboard relativist might argue that since
Cephalaspis
had played no notable part in fomenting this great revolution in thought, any evolutionary interpretation must be viewed as a new convention impressed upon old information—a new set of rules like the annual revision of Mah-Jongg hands imposed upon the same old tiles. But a realist would rightly reply that the tiles had changed as well. Agassiz had not resolved the anatomical status of
Cephalaspis
among the fishes; he could only affirm that the genus was both old and aberrant. Several of the greatest nineteenth-century evolutionists then studied
Cephalaspis
—including T. H. Huxley, E. R. Lankester, and E. D. Cope. From all their arguments and disagreements, one strong theme emerged:
Cephalaspis
and the ostracoderms were not just a grab bag of peculiar fishes. They formed a coherent group, with a large and consistent set of features all pointing to an anatomically primitive status among fossil vertebrates.
Cephalaspis
therefore became a prime candidate for theories about the ancestry of higher vertebrates. Evolution set the context, but new information about
Cephalaspis
fueled the debate.

Patten presented the most sophisticated case for the oldest theory of vertebrate origins—the attempt, dating to Geoffroy Saint-Hilaire in the early nineteenth century, to derive vertebrates from an inverted annelid or arthropod, a “worm that turned,” so to speak. Arthropods run their main nerve cords along their ventral (bottom) surface. The gut lies above, and the esophagus must therefore pierce through nervous tissue to end in a ventral mouth. In vertebrates, on the other hand, the main nerve tract, the spinal cord, is dorsal (on top), and the gut lies below. Turn an arthropod upside down, and you get the right order for vertebrates—nerves above guts. You also obtain a set of additional correspondences that some scientists have read as superficial and analogical, and others as deeply meaningful signs of evolutionary affinity.

But this act of inversion also produces some horrendous problems for the theory of arthropod ancestry. In particular, the vertebrate mouth does not pierce the brain and open on top of the head—though the old arthropod mouth would take this path in its supposedly inverted position. Proponents of the arthropod theory must therefore argue that this original mouth atrophied, and that vertebrates opened a new ventral version below the brain. No one has ever provided a good explanation for how such a topological transformation might plausibly occur.

A drawing from Patten’s 1912 book showing the superficial resemblance of a head shield of an ostracoderm fish (left) to a trilobite (right).
Courtesy of Department of Library Services, American Museum of Natural History
.

The arthropod theory, though venerable, suffered another major impediment that Patten tried to remedy. This theory was little more than an abstract argument based on a theoretical transformation without hard evidence in the form of intermediary creatures from the fossil record. Patten therefore returned to the oldest folk wisdom about
Cephalaspis
—the basic observation that had been judged false and treacherous ever since Agassiz. Maybe that first idea about a relationship with trilobites had some validity after all. Maybe
Cephalaspis
looked like an arthropod because it wasn’t all fish, as its back end seemed to proclaim. Maybe the head shield truly possessed some arthropod characters. Maybe ostracoderms did represent that long-sought intermediary group between arthropods and vertebrates.

Patten eventually argued himself into this position. He identified the marine arachnids (eurypterids and horseshoe crabs) as arthropod ancestors, and he classified ostracoderms, not as primitive jawless fishes, but as a transitional group between the two great phyla. He wrote in 1912:

Patten was more than a vertebrate anatomist; he also fancied himself a philosopher and moralist. As such, he used his theory of vertebrate origins as a centerpiece for one of the widest (and wildest) claims ever made for the sweep of evolutionary theory. In a series of works, including published class notes for Dartmouth courses in the late 1920s and in his general book
The Grand Strategy of Evolution
(1920), Patten tried to establish evolution as the source of all morality, proper conduct, and good human relations. He therefore becomes a convenient foil for our cardboard relativist who wishes to see little of the external world (if such a concept be intelligible at all) and much of social context in the claims of science.

I could not be more out of sympathy with Patten’s wider effort. I have never read a more tendentious or vainglorious attempt to establish a preferred social morality as the pathway and dictate of nature. I have no particular quarrel with Patten’s beliefs—a compendium of unassailable apple-pie virtues, featuring the value of service to others and the wisdom of self-restraint in a world of temptation. But I’ll be damned if nature can validate, or even address, such cultural hopes and preferences.

Patten argued that nature could instruct us if we learned her patterns and followed them in all our beliefs and dealings. He wrote in 1920:

This universal growth occurs along three cosmic axes—time, space, and rightness. The three-dimensional result is linear and necessary progress:

The direction of evolution also sets a moral imperative, for it “compels man to accept nature’s constructive rightness as his ethical standard, and to adopt her constructive methods as his moral code.”

But if nature’s progress is the source of our morality, then we had better be able to find an unambiguous direction in evolution. Patten bravely surveyed the entire tree of life, with its complex and ramifying branches shooting forth in a thousand separate directions, and managed to realign this intricate meshwork, with bold upper case, as “The Great Highway of Organic Evolution which leads from the lower forms of animal life up to man.”

To produce this remarkable change, Patten had to extract one lineage from life’s tree and depict it as a straight, central highway. He then had to view all other groups as side roads leading to the dirt of nowhere. But how can a central artery be discovered (with humans on top) if, as generally held, vertebrates go back into the mists of time and do not arise directly from any other complex phylum (but share closest ties with the lowly echinoderms)? How can we specify a Great Highway if arthropods, representing some 80 percent of animal species and including the most structurally complex invertebrates, do not lie firmly upon this main route?

Obviously, then, the concept of a Great Highway demands a direct linkage of lower arthropod to higher vertebrate. And if no highway can be found, then we have no natural basis for morality and no primacy of evolution among the disciplines. Patten therefore called upon
Cephalaspis
and the ostracoderms to perform the greatest of all services—to form the link that would secure both the direction of life and the laws of moral conduct. Patten explicitly cited his arthropod theory of vertebrate origins as the key to his entire system:

Patten even thought that he had finally found a mechanism, in his theory of necessary progress, for that most improbable claim of the arthropod theory—the closure of the old mouth above the brain and the opening of a new version below. He argued that progress must be marked by increasing size of the brain, and that expanding nervous tissue would choke off the old brain-piercing esophagus, forcing construction of a new mouth:

An illustration of Patten’s Great Highway of animal evolution from his 1920 book. Note that he places ostracoderms between arthropods and vertebrates.
Courtesy of Department of Library Services, American Museum of Natural History
.

Our cardboard relativist may now exult. Patten’s personal need to find moral answers in evolution, and the early twentieth-century vogue among paleontologists for reading life’s history as a tale of linear progress, surely fueled his improbable interpretation of ostracoderms as transitional between arthropods and vertebrates. But our realist shouts “wait!” A factual question must still be resolved. People may believe correct things for the damnedest and weirdest of flawed reasons. We still have to know the zoological status of
Cephalaspis
—for this genus ranks somewhere in life’s genealogy no matter what cultural blinders we may wear at any moment. We still must find out whether Patten was right or wrong.