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Grandeur in this story of life

Posted on: Tuesday, 19 August 2003, 06:00 CDT

To misquote Darwin only slightly, there is grandeur in this story of life - and more than a little wonder, too. Which is itself sort of wondrous: as questions (and, here and there, actual answers) about the origin, evolution, diversity, and even the meaning of life on Earth have moved from the realm of theology and philosophy into astronomy, geology, and biology, they have lost none of their ability to inspire awe - or, in the stubbornly curmudgeonly, at least a sense of grudging respect for what nature has wrought.

As scientists explore the conditions necessary to life, they are seeing hints that life, particularly the intelligent variety, may not be a mere accident of serendipity on one insignificant, wet little world out in the boondocks of a not-especially-special galaxy. Instead, they cannot help but be struck by the fine-tuning required; that is, fundamental quantities in nature such as the expansion rate of the universe, the relative strength of gravity, and the nuclear binding force have exactly the values needed to create structure in the cosmos and to produce stable atoms (you know - planets for life to live on, stars to warm them, and matter to build living things). If the nuclear binding force were .007 instead of .006, for instance, we would have a universe composed of nothing but hydrogen. No matter how devoutly you believe (with the chaotician in Jurassic Park) that "life will find a way," it's not immediately obvious how to get life out of nothing but hydrogen atoms. By one recent calculation, the chance that we'd wind up with the requisite values of these fundamental constants is 10 raised to the 220th power, which is larger than the number of atoms in the universe.

The life-giving coincidences of nature s numbers have led scholars like Christian de Duve to wonder whether inanimate matter has been deeply imbued with a life-forming blueprint. "Chance," he has written, "may produce life and mind obligatorily, not once but many times." Life, on Earth and very possibly elsewhere, he argues, is thus no mere accident but an inevitable child of the basic laws of the cosmos, "written into the fabric of the universe."

Yet, inevitability has its limits. Contingency, in the sense of being dependent on historical accident and chance, seems to have stepped in as life developed from single-celled organisms to multicellular ones and then exploded into the biodiversity that has marked life on Earth. The fossil record is a series of fits and starts - "punctuated equilibrium," Niles Eldredge and the late Stephen Jay Gould called it - in which species thrive with little morphological change and then suddenly try all sorts of anatomical experiments. "Anatomical change rarely shows up in the fossil record," notes Eldredge, but when it does, as when species go extinct, "it's because of environmental change." These evolution- nudging changes - the neighborhood got hotter, colder, wetter, drier - seem to affect many distantly-related organisms at once. "In South Africa 2.5 million years ago, pigs, birds, and grasses all went extinct simultaneously, after which we see the generation of new species in each of these clades," notes Eldredge. "That reflects changes in the environment." Even if life qua life is inevitable in the universe, the actual form it takes seems fundamentally contingent and unpredictable. That holds true for the emergence of Homo sapiens and our even older hominid ancestors. Our existence is contingent on climatic changes in Africa millions of years ago. If things had gone a bit differently, maybe porpoises would be the dominant intelligent life on the planet.

The diversity of life seems to have undergone a veritable explosion in the last 250 million years. Originally dismissed as an artifact of the fossil record, the leap in diversity - it seems to have doubled since the dinosaurs' demise 65 million years ago - now not only looks real, but may itself be a phoenix-from-the-ashes phenomenon. "You see these explosions of species after extinctions," notes Eldredge. The six mass extinctions of life on Earth (the first was at the end of the Cambrian 500 million years ago, and the last at the end of the Cretaceous 65 million years ago) wiped out as many as 90 percent of the species alive at the time. The causes of the extinctions are still the subject of lively debate, but whether asteroids or volcanoes or some combination thereof are to blame, nothing about them seems woven into the woof and weave of the universe.

Short of finding some alien being who was videotaping the whole thing, we will likely never know how life first emerged from abiotic ingredients (at best, we might figure out how it could have emerged), or what precise environmental shocks nudged it in this or that morphological direction. Unless . . . We may be approaching a point when scientists who study the origin and evolution of life will recognize that they have been using the fossil record much the way a drunk uses a lamppost: for support, not illumination. In search of the latter, researchers like Sean Carroll are studying evolution not through whatever shadows of life the sedimentary rocks might hold, but through embryological development. "Evo-devo," a term born in the mid-1990s, marries two approaches: studying the evolution of the genetic makeup of organisms, and studying how genes mastermind the development of an organism from conception onward. The conservation of genes across millennia - a DNA sequence that controls body plan, called Hox genes, seems to have persisted unchanged from organisms 700 million years ago to today - shows that once nature finds a solution she doesn't cast it aside anytime soon. Evo-devo might, finally, allow paleontologists to go beyond documenting changes in form as a result of evolution to inferring how those changes came about (even without ET's video). Surely, we have glimpsed only the tiniest fraction of the "grandeur in this view of life."

Sharon Begley is a science columnist for The Wall Street Journal.

Copyright Minnesota Monthly Publications Aug 2003

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