Evo/Devo and the lungfish: the last gasp of intelligent design
Gerald Weissmann, Editor-in-Chief
The fishes of the early and middle Devonian found themselves forced to choose between the invading salt water marshes and the isolated fresh-water pools which periodically contracted into stagnant swamps or hard mud flats... The more advanced of the fishes, however, in order to survive in the stagnant waters of the continents, took to swallowing air and thus invented lungs and prepared the way for the evolution of the terrestrial vertebrates.
Homer Smith (1)
The scientists used state-of-the-art statistical and molecular methods to unravel the evolution of the hormone aldosterone. They resurrected the ancestral receptor gene—which existed more than 450 million years ago, before the first animals with bones appeared on Earth... The experiments showed that the receptor had the capacity to be activated by aldosterone long before the hormone actually evolved.
Bridgham, et al. (2)
This weekend at the New York Auto Show, the taxicab of the future will be on display. Designers say the cab is so futuristic that the driver will be from a country that doesn’t even exist yet.
Conan O’ Brien (3)
EVO/DEVO AND THE CONQUEST OF LAND
Creationists, fans of "intelligent design" and other flat-earth zanies have been playing defense since December 2005 when Judge Jones of Dover, Pennsylvania, ruled that intelligent design (ID) had no place in science classrooms. After Dover, bills designed to subvert the teaching of evolution failed to pass even in such conservative states as Kansas, Utah, and South Carolina.
Meanwhile, newer studies in evolutionary and developmental molecular biology (Evo/Devo) have left the favorite notions of intelligent design in Devonian mud. At Dover, the ID apologists advanced the concept of "irreducible complexity," i.e., some systems are so complex that they had to be designed in one flash by one intelligence—guess Who (4) ? It turns out that molecular genetics can reach into the Devonian seas of 400—500 million years ago to explain "Aldosterone and the Conquest of Land (5) ." Evo/Devo has puzzled out a system as "irreducibly" complex as the human kidney and its hormonal regulation. Random mutations, over time, in marine creatures adapted a system that responded to stress in the sea (via cortisone) to one that retained salt and water when lungfish crawled ashore (via aldosterone). Genes for the cortisol receptor anteceded those of the aldosterone receptor and the p450 enzyme required to make the salt-and-water hormone. The receptor was there before the ligand existed (2 , 5) . As Conan O’Brien quipped, the taxi was there before the country was invented (3) .
ONTOGENY RECAPITULATES PHYLOGENY (SORT OF)
But don’t count the faithful out. The pulpits have sharpened their attacks on Darwin and company, while presidential candidate Sam Brownback blames human embryonic stem cell research for "the destruction of young human lives (6) ." Unlike the intelligent design folks, creationists like Brownback et al. take particular offense at the notion of Evo/Devo, the academic discipline based on interactions between evolution and developmental biology. They take straight aim at Ernst Haeckel, whom they hold accountable for having launched Evo/Devo in the first place. Creationists have joined their belief that Darwin contradicts scripture to the conviction that Haeckel is the devil incarnate—wasn’t he the German who claimed that little human embryos look like fish or larval salamanders? Creation magazine points the finger:
Most people have heard of or been taught the idea that the human embryo goes through (or recapitulates) various evolutionary stages, such as having gills like a fish, a tail like a monkey, etc., during the first few months that it develops in the womb. The idea ... has not only been presented to generations of biology/medical students as fact, but has also been used for many years to persuasively justify abortion. Abortionists claimed that the unborn child being killed was still in the fish stage or the monkey stage, and had not yet become a human being. This idea (called embryonic recapitulation) was vigorously expounded by Ernst Haeckel from the late 1860s to promote Darwin’s theory of evolution in Germany, even though Haeckel did not have evidence to support his views. [7 ]
Not quite. First of all, the early human embryo does look like a little fish (almost) with a tail and branchial clefts under the chin, just where gills develop in lower forms (more or less). Haeckel himself argued that recapitulation doesn’t imply identity (7) . Second, Haeckel expanded Darwin’s description of natural selection to include the rest of nature. It’s no accident that Joe Thornton, who made the aldosterone discovery, works at Oregon’s Ecology and Evolutionary Biology Center. Haeckel coined the word "ecology" in 1866 to describe the study (logos) of the house (oikos) of nature: Darwinian selection takes place in a changing environment. Finally, Haeckel’s phylogenetic drawings have been re-examined and found to be more illustrative than evidentiary. Nevertheless, their heuristic value is now generally accepted:
Haeckel recognized the evolutionary diversity in early embryonic stages, in line with modern thinking. Haeckel’s much-criticized embryo drawings are important as phylogenetic hypotheses, teaching aids, and evidence for evolution ... Despite his obvious flaws, Haeckel can be seen as the father of a sequence-based phylogenetic embryology (7) .
To the legions of the faithful, however, Haeckel remains bad news. From a website aptly named "Apologetics Press" comes the old canard:
Dr. Haeckel was an accomplished artist, as well as an anatomist. He used his art talent to falsify some of the drawings that accompanied his research articles on animal and human embryos, in order to make it appear as if embryonic recapitulation were true—when, in fact, it was not (8) .
Scores of high-tech websites and amateur blogs point the fickle finger of shame at Haeckel. Folks who insist that the fossil record "proved the Bible and God right and evolution wrong (9) " and who cite junk science to explain that "the only way we know for a DNA to be altered is through a meaningful intervention from an outside source of intelligence (10) ," also complain that schools and churches have been subverted by "academics kowtowing to every pronouncement made by Darwin and his God-hating successors"—like Haeckel (11) . The dells are alive with the sound of malice.
FROM FISH TO PHILOSOPHER
Haeckel’s notion of the phylogenetic law received early approval from Darwin. In his The Descent of Man (1871) Darwin chimed in with:
He who wishes to see what ingenuity and knowledge can effect, can consult Dr. Haeckel’s work ... As the class of fishes is the most lowly organized and appeared before the others we may conclude that all the members of the vertebrate kingdom are derived from some fish-like animal, for they [all] have much in common, especially in their embryonic stage (12) .
The clearest example of "having much in common in their embryonic stage," i.e. phylogeny recapitulating ontogeny, is that of the human kidney. Homer Smith’s classic The Evolution of the Kidney (1942) puts it neatly:
In the ontogenic development of the human embryo, the glomerulus is not brought into conjunction and connected with the tubule of the metanephros until some time after the tubule has been formed ... this interval between the development of the tubule and the glomerulus is an ontogenic recapitulation of the phylogenetic interval which separated their evolution (1) .
Smith, Professor of Physiology at NYU School of Medicine, was as broadly cultivated, as fine an artist (albeit in prose) and as influential in his own field as Haeckel; he was recognized as the "dean of renal physiology" at mid 20th century (1) . His contributions included the introduction of inulin to measure glomerular filtration rate, the use of dyes, such as p-aminohippurate to measure renal blood flow, and development of the concept of Tm, the maximal rate at which a substance is taken up by the kidney from blood or tubules. Together with Herbert Chasis and William Goldring, he showed that much of human hypertension is due to peripheral vasoconstriction; an observation that made possible today’s treatments for high blood pressure.
Smith was also a skeptical thinker, whose many essays, lectures, and books echoed the humanist tradition of the first chair of Physiology at NYU, John William Draper (History of the Conflict Between Religion and Science, 1874). In praising the joys of here and now over the promise of pie in the sky, he’d repeat Isak Dinesen’s jibe "What is man, when you come to think upon him, but a minutely set, ingenious machine for turning, with infinite artfulness, the red wine of Shiraz into urine (13) ?" Smith had a still higher view of renal function: "Superficially it might be said that the function of the kidneys is to make urine; but in a considered view one can say that the kidneys make the stuff of philosophy itself (14) ."
THE LUNGFISH AND THE PADRE
By the age of 37, Homer Smith had become a national celebrity for his best-selling book Kamongo, or The Lungfish and the Padre (1932). An eloquent exercise in popular Darwinism, the book remained in print for 20 years. Smith had traveled to the papyrus marshes of eastern Lake Victoria to bring back living samples of the African lungfish (kamongo to the natives) in order to apply his inulin methods to a species in which glomerulus and tubules had not quite meshed. The lungfish has twin lungs and can breathe in both air and water, but must have air available or it will drown. Its lungs permit it to survive in times of drought or dust, when it encysts itself deep into soft mud:
When water drains away, the fish can at last breathe without moving, and it curls up with its tail across the top of its head, covering the eyes. Its body is coated with a slimy mucus secreted by the skin, and as this mucus dries it hardens into a brown, parchment-like, waterproof cocoon that envelopes the body closely, extending into all exposed crevices. The only opening is a short funnel where the cocoon extends between the lips and teeth, and through which the fish breathes (15) .
Lungfish can live in this chamber for up to four years in dry spells, but by and large the rains return within half a year. They drown in neat water, and dessicate in air. Perhaps that’s why their remnants occupy such a tiny niche in our vast eco-system.
Kamongo, the book, is cast as a dialogue between an American scientist, Joel, (Smith’s alter ego) and an Anglican missionary priest. The setting is the voyage home from East Africa north to the Suez Canal aboard the S.S. Dumbea [sic]. Joel and the priest talk of cosmic stuff and evolution. Joel tells the padre the story of the lungfish; a dead end in evolution, and the two have very different views of what the story means to mankind. Joel has concluded that the notion of any over-riding universal intelligence is an illusion. Man’s brain, argues Joel, may be like a kamongo’s lung, both ingenious developments, but neither leading to any ulterior end. Joel finishes his argument by calling life "an eddy in the Second Law of Thermodynamics." The priest, sympathetic throughout as a character, remains unconvinced and responds with an appeal to the ineffable, "miracles happen." The two travelers part, neither understanding the other.
Written only a few years after the Scopes trial, and while the teaching of Darwinian evolution was still illegal in several states, the book touched a public nerve. It was picked by the Book-of-the-Month Club in April 1932, the same year that Faulkner’s Light in August and James T. Farrell’s Studs Lonigan shared the honor.
EVO/DEVO AND EINSTEIN
In the public sphere not too much has changed since Kamongo; we’ve now had Dover, followed by Richard Dawkins on the best-seller list. But in the realm of Evo/Devo, more has happened. Jean Joss, of McQuarrie University in Australia, has suggested that Devonian lungfish probably included metamorphosis in their life cycle. They have an enormous genome, 132 pg/nuclear DNA vs. 3.4 for humans or other mammals (17) ; that brackets lungfish with the large genomes of larval salamanders (see Haeckel’s illustration, above). In this modern tree of life, the larval forms of Devonian lungfish became the direct ancestors of tetrapods and, needless to say, our ancestors as well. And in utero, our twin, fetal lungs begin as small paired pouches under the chin. Devo recapitulates Evo, as Haeckel predicted.
Finally, on the intelligent design front, I’d go along with Albert Einstein in his Introduction to Homer Smith’s last book:
Homer Smith’s Man and His Gods (1952) is a broadly conceived attempt to portray man’s fear-induced animistic and mythic ideas with all ... the boundless suffering which, in its end results, this mythic thought has brought upon man. This is a biologist speaking, whose scientific training has disciplined him in a grim objectivity rarely found in the pure historian. His historical picture closes with the end of the nineteenth century, and with good reason. By that time it seemed that the influence of these mythic, authoritatively anchored forces which can be denoted as religious, had been reduced to a tolerable level in spite of all the persisting inertia and hypocrisy (18) .
If we’re lucky, the influence of those mythic forces can be reduced to a tolerable level once more.
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The FASEB Journal. 2007;21:1623-1626. © 2007 FASEB.