theme for an essay — so my literary thanks 

 go out to them as well). The first item 

 comes from the very beginning, the sec- 

 ond from the middle, and the third from 

 the latest moment in the history of animal 

 life. The three seem just as different in sub- 

 ject — for the first examines evolutionary 

 rate; the second, interaction among organ- 

 isms; and the third, biogeography, or place 

 of origin for a key species. 



But the three stories are linked at a level 

 sufficiently abstract to evoke the underly- 

 ing attitudes so basic to one's particular 

 being that popular culture speaks of a per- 

 son's "philosophy of life," or "worldview." 

 Scholars have also struggled with this no- 

 tion of a personal or social model so per- 

 vasive that all particulars are judged in its 

 light. Being scholars, they may use a fancy 

 German term like Weltanschauung, which 

 sounds complex but only means "outlook 

 upon the world." In the most celebrated 

 use in a social sense, T. S. Kuhn referred 

 to the shared worldview of scientists as a 

 paradigm (see his classic 1962 book. The 

 Structure of Scientific Revolutions). Such 



paradigms, in Kuhn's view, are so con- 

 straining, and so unbreakable in their own 

 terms, that fundamentally new theories 

 must be imported from elsewhere (in- 

 sights of other discipUnes, conscious radi- 

 calism of young rebels within a field) and 

 must then triumph by rapid replacement 

 (scientific revolution), rather than by in- 

 cremental advance. But the most eloquent 

 testimony to the power and pervasiveness 

 of worldviews was surely provided by 

 Gilbert and Sullivan's Private Willis (in 

 lolanthe), as he mused on guard duty out- 

 side the Victorian House of Commons: 



I often think it's comical 



How Nature always does contrive 



That every boy and every gal 



That's bom into the world alive 



is either a Uttle Liberal 



Or else a little Conservative! 



Nothing is more dangerous than a dog- 

 matic worldview — nothing more con- 

 straining, more blinding to innovation, 

 more destructive of openness to novelty. 

 But on the other hand, a fruitful worldview 



Soaxu 

 'Si 



'There they go on their annual migration, the 

 wildebeests and Professor Lippincott. ..." 



is the greatest shortcut to insight and the 

 finest prod for making connections — in 

 short, the best possible agent for a 

 Peircean abduction. So much in our mate- 

 rial culture is both alluring and dangerous 

 at the same time — try fast cars and high- 

 stakes poker for starters. Why shouldn't a 

 fundamental issue in our intellectual lives 

 have the same property? 



In short, I realized that my linkage of 

 the three issues, and my lack of surprise at 

 claims reported in newspapers as startling, 

 emanated from a worldview, or model of 

 reality, different in some crucial respects 

 from the expectations held by many scien- 

 tific colleagues and by the general public. I 

 do not know that my view is more correct; 

 I do not even think that "right" and 

 "wrong" are good categories for assessing 

 complex mental models of external real- 

 ity — for models in science are judged as 

 useful or detrimental, not as true or false. 



I do know that chosen models dictate 

 our parsing of namre and either channel 

 our thoughts toward novel insight or blind 

 us to evident and important aspects of re- 

 ality. Beauty must be in the eye of the be- 

 holder — and our minds are as varied as 

 our hairstyles. "For great is truth, and shall 

 prevail" — but we only get there along 

 pathways of our own mental construction. 

 Science is as resolutely personal an enter- 

 prise as art, even if the chief prize be truth 

 rather than beauty (although artists also 

 seek truth, and good science is profoundly 

 beautiful). 



1. Timing the Cambrian explosion: 

 How fast is fast? Paleontologists have long 

 known, and puzzled over, the rapid ap- 

 pearance of nearly all major animal phyla 

 during a short interval at the beginning of 

 the Cambrian period (a subject frequently 

 treated in these essays and in my book 

 Wondetful Life). The earth's fossil record 

 extends back 3.5 billion years to the earli- 

 est rock sufficiently unaltered by later heat 

 and pressure to preserve traces of ancient 

 organisms. But with the exception of some 

 multicellular algae that play no role in the 

 genealogy of animals, all life, including 

 the ancestors of animals, remained unicel- 

 lular for five-sixths of subsequent history, 

 until about 550 million years ago, when an 

 evolutionary explosion introduced all the 

 major groups of animals in just a few mil- 

 lion years. 



When geologists use die word explo- 

 sion, you must take this expression with a 

 grain of salt and recognize that, in our 

 world, explosions have very long fuses. 

 No one has ever doubted that the Cam- 

 brian explosion must be measured in mil- 



16 Natural History 2/94 



