The crapshoot of history

Originally published 6 November 1989

Stephen Jay Gould has writ­ten his best book yet.

Won­der­ful Life: The Burgess Shale and the Nature of His­to­ry is the sto­ry of some remark­able fos­sils from the moun­tains of west­ern Cana­da, and a spright­lier intro­duc­tion to the his­to­ry, meth­ods, and phi­los­o­phy of sci­ence would be hard to imag­ine. Sim­ply put, Won­der­ful Life is won­der­ful — required read­ing for any­one who wants to under­stand the nature of science.

But “the nature of his­to­ry”? Ah, that’s some­thing else. Gould’s ambi­tious sub­ti­tle promis­es more than the book deliv­ers. Sure enough, he dish­es up the Burgess Shale in all its won­der­ful detail, but the nature of his­to­ry proves tan­ta­liz­ing­ly elusive.

The Burgess Shale is a mud­stone quar­ry in the Cana­di­an Rock­ies that in 1909 yield­ed a trea­sure trove of fos­sils to Charles D. Wal­cott, head of the Smith­son­ian Insti­tu­tion and one of the great­est pale­on­tol­o­gists of his time. The muds were deposit­ed dur­ing the Mid­dle Cam­bri­an peri­od of Earth his­to­ry, 530 mil­lion years ago, near a reef on the floor of an ancient sea. The fos­sils are pre­served with pho­to­graph­ic fideli­ty. They reveal a bizarre zoo of sea-dwelling ani­mals, typ­i­cal­ly an inch or two long, includ­ing five-eyed Opabinia, spike-legged Hal­lu­ci­ge­nia, and pineap­ple-shaped Wiwax­ia, all now extinct.

Improbable animals

The sep­a­rate parts of these ani­mals look vague­ly famil­iar, but jug­gled into wild­ly improb­a­ble com­bi­na­tions, like one of those chil­dren’s toys where by turn­ing the seg­ments of a cylin­der one cre­ates fan­tas­tic ani­mals — a giraf­fe’s head on a horse’s body with ele­phant legs. What to make of these “weird won­ders,” so unlike any­thing seen before or since? Wal­cott found a place for each of the crea­tures (a cou­ple of dozen alto­geth­er) with­in con­ven­tion­al branch­es of the tree of life — worms or arthro­pods. For all their strange­ness, Wal­cott con­sid­ered all the Burgess ani­mals ances­tral­ly relat­ed to present forms of life.

As Gould makes clear, Wal­cott “shoe­horned” the Burgess ani­mals into tra­di­tion­al cat­e­gories because he was con­vinced that evo­lu­tion is a path­way of nec­es­sary progress lead­ing from our most prim­i­tive ances­tor to our­selves, the fittest form of life on Earth and the crown of cre­ation. It did­n’t occur to him that the major­i­ty of ani­mals in the Burgess sea might be evo­lu­tion­ary dead ends, alter­nate designs for life that some­how did­n’t work out. And that’s where mat­ters stood until the late 1960s when Har­ry Whit­ting­ton of Cam­bridge Uni­ver­si­ty decid­ed to take a fresh look at the fos­sils that had gath­ered dust for 50 years in lab­o­ra­to­ry cabinets.

As Whit­ting­ton and his col­leagues Derek Brig­gs and Simon Con­way Mor­ris painstak­ing­ly recon­struct­ed the Burgess ani­mals an aston­ish­ing truth emerged: Many of these crea­tures are so fun­da­men­tal­ly dif­fer­ent from any­thing alive on Earth today as to require the cre­ation of entire­ly new phy­la (cat­e­gories) of life — and give a strange new twist to the sto­ry of evolution.

Pale­on­tol­o­gists have long rec­og­nized that some­thing remark­able hap­pened ear­ly in the Cam­bri­an peri­od of Earth his­to­ry, just pri­or to the depo­si­tion of the Burgess Shale. For 3 bil­lion years the Earth had been inhab­it­ed only by micro­scop­ic, sin­gle-celled organ­isms. Then sud­den­ly there appeared a vari­ety of mul­ti-celled crea­tures — sponges, trilo­bites, and jel­ly­fish, for exam­ple — includ­ing the remote ances­tors of all fam­i­lies of life present­ly on Earth.

Appar­ent­ly this Cam­bri­an explo­sion was even more pro­lif­ic than we had pre­vi­ous­ly imag­ined. The Burgess Shale con­tains not only the ances­tors of present life, but ani­mals with anatomies wild­ly dif­fer­ent than any­thing exist­ing today. For a time these improb­a­ble Burgess beasts shared the Earth with our more famil­iar ances­tors. Then occurred what Gould calls a “great dec­i­ma­tion,” and most of the Burgess ani­mals became extinct. We don’t know the nature of the dis­as­ter, or even how quick­ly it occurred. But nev­er again would life on Earth be so rad­i­cal­ly diverse.

Contingent on chance?

Now Gould draws his moral: Evo­lu­tion is a crap­shoot. The Burgess fos­sils give no indi­ca­tion that some of these ani­mals were more or less fit than oth­ers. When the great dec­i­ma­tion came, sur­vival depend­ed on luck, not fit­ness or design. Rewind the tape of evo­lu­tion back to the time of the Burgess Shale, play it again, and no crea­ture remote­ly like Homo sapi­ens would be like­ly to emerge. Con­cludes Gould: His­to­ry is con­tin­gent — upon a myr­i­ad episodes of chance. We are an acci­den­tal detail, not the pur­pose of creation.

I hap­pen to agree with Gould’s con­clu­sion, but I ques­tion whether the strict con­tin­gency of his­to­ry is a nec­es­sary les­son of the Burgess Shale. Many of us believed that his­to­ry is mod­i­fied by chance long before we ever heard of the Burgess dead-end ani­mals. Even Wal­cot­t’s tra­di­tion­al tree of life, dri­ven upwards by ran­dom muta­tions act­ed upon by nat­ur­al selec­tion (sur­vival of the fittest), gave ample rea­son to appre­ci­ate how force­ful­ly chance sifts and shuf­fles fate. But sure­ly one can accept con­tin­gency with­out aban­don­ing the idea of an order, or even direc­tion, for evolution.

Con­tin­gency, cat­a­stro­phe, and chaos are cur­rent­ly fash­ion­able in sci­ence, but I’ll opt for a healthy dose of good, old-fash­ioned deter­min­ism. If the tape of life were replayed from the time of the Burgess Shale, I would not be sur­prised if a crea­ture of a cer­tain opti­mum size, agili­ty, and mobil­i­ty, with ver­sa­tile sen­so­ry organs and intel­li­gence did­n’t again emerge out of the work­ing of Dar­win­ian nat­ur­al selec­tion, or any oth­er dynam­ic of evo­lu­tion that is not pure chance. That crea­ture would­n’t be us exact­ly, but an oth­er us, a walk­ing, talk­ing, think­ing descen­dant of unlucky, five-eyed Opabinia, per­haps, or pineap­ple-shaped Wiwax­ia. Not Homo, but cer­tain­ly sapi­ens, out there chip­ping fos­sils out of the moun­tain or sit­ting in Cam­bridge pon­der­ing their meaning.

His­to­ry is con­tin­gent, but it ain’t nec­es­sar­i­ly a crap­shoot. By deify­ing the roll of the dice Gould out-Wal­cotts Wal­cott, who imposed upon the Burgess fos­sils his own notion of design. Strict con­tin­gency, like the idea of fit­ness, is a mat­ter of faith, informed by expe­ri­ence per­haps, but not a nec­es­sary con­se­quence of the Burgess Shale or any oth­er fos­sils. Gould sim­ply makes his moral too grand for his sto­ry. But the sto­ry is mar­velous, and the moral not absurd.