Tffls View of Life 



Hooking Leviathan by Its Past 



Two tales of tails confirm the theory of the whale's return to the sea 

 by Stephen Jay Gould 



The landscape of every career contains 

 at least a few crevasses, and usually a 

 more extensive valley or two — for every 

 Ruth's bat, a Buckner's legs; for every lop- 

 sided victory at Agincourt, a bloodbath at 

 Antietam. Darwin's first edition of Origin 

 of Species contains some wonderful in- 

 sights and magnificent lines, but this mas- 

 terpiece also includes a few notable clink- 

 ers. Darwin became most embarrassed 

 about the following passage, curtailed and 

 largely expunged from following editions 

 of his book: 



In North America the black bear was seen 

 by Heame swimming for hours with widely 

 open mouth, thus catching, like a whale, in- 

 sects in the water. Even in so extreme a case 

 as this, if the supply of insects were con- 

 stant, and if better adapted competitors did 

 not already exist in the counUry, I can see no 

 difficulty in a race of bears being rendered, 

 by natural selection, more aquatic in their 

 structure and habits, with larger and larger 

 mouths, till a creature was produced as 

 monstrous as a whale. 



Why did Darwin become so chagrined 

 about this passage? His hypothetical tale 

 may be pure speculation and conjecture, 

 but the scenario is not entirely absurd. 

 Darwin's discomfort arose, I think, from 

 his failure to follow a scientific norm of a 

 more sociocultural nature. Scientific con- 

 clusions supposedly rest upon facts and in- 

 formation. Speculation is not entirely 

 taboo, and may sometimes be necessary 

 faute de mieux. But when scientists pro- 

 pose truly novel and comprehensive theo- 

 ries — as Darwin tried to do in advancing 

 natural selection as the primary mecha- 

 nism of evolution — they need particularly 

 good support, and invented hypothetical 

 cases just don't supply sufficient oomph 

 for crucial conclusions. 



Natural selection (or the human ana- 



logue of differential breeding) clearly 

 worked at small scale — in the production 

 of dog breeds and strains of wheat, for ex- 

 ample. But could such a process account 

 for the transitions of greater scope that set 

 our concept of evolution in the fiillness of 

 fime: the passage of reptilian lineages to 

 birds and mammals; the origin of humans 

 from an ancestral stock of apes? For these 

 larger changes, Darwin could provide little 

 direct evidence, for a set of well-known 

 and much lamented reasons based on the 

 extreme spottiness of the fossil record. 



Some splendid cases began to accumu- 

 late in years following the Origin of Spe- 

 cies, most notably the discovery in 1861 of 

 Archaeopteryx, an initial bird chock-full 

 of reptiUan features, and the first findings 

 of human fossils late in the nineteenth cen- 

 tury. But Darwin had little to present in his 

 first edition of 1 859, and he tried to fill this 

 factual gap with hypothetical fables about 

 swimming bears eventually turning into 

 whales — a fancy that yielded far more 

 trouble in easy ridicule than aid in useful 

 illustration. Just two years after penning 

 his bear-to-whale tale, Darwin lamented in 

 a letter to a friend (James Lamont, Febru- 

 ary 25, 1861), "It is laughable how often 1 

 have been attacked and misrepresented 

 about this bear." 



The supposed lack of intermediary 

 forms in the fossil record remains the fun- 

 damental canard of current antievolution- 

 ism. Such transitional forms are scarce, to 

 be sure, and for two sets of good rea- 

 sons — geological (the gappiness of the 

 fossil record) and biological (the episodic 

 nature of evolutionary change, including 

 patterns of punctuated equilibrium and 

 transition within small populations of lim- 

 ited geographic extent). But paleontolo- 

 gists have discovered several superb ex- 

 amples of intermediary forms and 



sequences, more than enough to convince 

 any fair-minded skeptic about the reality 

 of life's physical genealogy. 



The first "terrestrial" vertebrates re- 

 tained six to eight digits on each limb 

 (more like a fish paddle than a hand), a 

 persistent tail fin, and a lateral Une system 

 for sensing sound vibrations underwater. 

 The anatomical transition from reptiles to 

 mammals is particularly well documented 

 in the key anatomical change of jaw artic- 

 ulation to hearing bones. Only one bone, 

 called the dentary, builds the mammalian 

 jaw, while reptiles retain several small 

 bones in the rear part of the jaw. We can 

 trace, through a lovely sequence of inter- 

 mediates, the reduction of these small rep- 

 tilian bones and their eventual disappear- 

 ance or exclusion from the jaw, including 

 the remarkable passage of the reptilian ar- 

 ticulation bones into the mammalian mid- 

 dle ear (where they become our malleus 

 and incus, or hanmier and anvil). We have 

 even found the ti"ansitional form that cre- 

 ationists often proclaim inconceivable in 

 theory — for how can jawbones become 

 ear bones if intermediaries must have un- 

 hinged jaws before the new joint forms? 

 The fi-ansitional species maintains a dou- 

 ble jaw joint, with both the old articulation 

 of reptiles (quadrate to articular bones) 

 and the new connection of mammals 

 (squamosal to dentary) already in place! 

 Thus, one joint could be lost, with passage 

 of its bones into the ear, while the other ar- 

 ticulation continued to guarantee a prop- 

 erly hinged jaw. 



Still, our creationist incubi, who would 

 never let facts spoil a favorite argument, 

 refuse to yield, and continue to assert \ht 

 absence of all transitional forms by ignor- 

 ing those that have been found and contin- 

 uing to taunt us with admittedly frequent 

 examples of absence. Darwin's difficulty 



8 Natural History 5/94 



