I Have Landed

Natural History, Dec, 2000 by Stephen Jay Gould

In the final essay of this twenty-seven-year series, the author reflects on continuity--from family history to the branching lineage of terrestrial life.

As a young child, thinking as big as big can be and getting absolutely nowhere for the effort, I would often lie awake at night, pondering the mysteries of infinity and eternity and feeling pure awe (in an inchoate, but intense, boyish way) at my utter inability to comprehend. How could time begin? For even if a God created matter at a definite moment, then who made God? An eternity of spirit seemed just as incomprehensible as a temporal sequence of matter with no beginning. And how could space end? For even if a group of intrepid astronauts encountered a brick wall at the end of the universe, what lay beyond the wall? An infinity of wall seemed just as inconceivable as a never-ending expanse of stars and galaxies.

I will not defend these naive formulations today, but I doubt that I have come one iota closer to a personal solution since these boyhood ruminations so long ago. In my philosophical moments--and not only as an excuse for personal failure, for I see no sign that others have succeeded--I rather suspect that the evolved powers of the human mind may not include the wherewithal for posing such questions in answerable ways (not that we ever would, should, or could halt our inquiries into these ultimates).

However, I confess that in my mature years, I have embraced the Dorothean dictum: yea, though I might roam through the pleasures of eternity and the palaces of infinity (not to mention the valley of the shadow of death), when a body craves contact with the brass tacks of a potentially comprehensible reality, I guess there's no place like home. And within the smaller, but still tolerably ample, compass of our planetary real estate, I would nominate as most worthy of pure awe--a metaphorical miracle, if you will--an aspect of life that most people have never considered but that strikes me as equal in majesty to our most spiritual projections of infinity and eternity, while falling entirely within the domain of our conceptual understanding and empirical grasp: the continuity of etz chayim, the tree of earthly life, for at least 3.5 billion years, without a single microsecond of disruption.

Consider the improbability of such continuity in the conventional terms of ordinary probability: Take any phenomenon that begins with a positive value at its inception 3.5 billion years ago, and let the process regulating its existence proceed through time. A line marked zero runs along below the current value. The probability of the phenomenon's descent to zero may be almost incalculably low, but throw the dice of the relevant process billions of times and the phenomenon just has to hit the zero line eventually.

For most processes, the prospect of such an improbable crossing bodes no permanent ill, because an unlikely crash (a year, for example, when a healthy Mark McGwire hits no home runs at all) will quickly be reversed, and ordinary residence well above the zero line reestablished. But life represents a different kind of ultimately fragile system, utterly dependent upon unbroken continuity. For life, the zero line designates a permanent end, not a temporary embarrassment. If life had ever touched that line for one fleeting moment at any time during 3.5 billion years of sustained history, neither we nor a million species of beetles would grace this planet today. A single handshake with voracious zero dooms all that might have been, forever after.

When we consider the magnitude and complexity of the circumstances required to sustain this continuity for so long--and without exception or forgiveness in each of so many components--well, I may be a rationalist at heart, but if anything in the natural world merits designation as "awesome," I nominate the continuity of the tree of life for 3.5 billion years. Earth experienced severe ice ages but never froze completely, not for a single day. Life fluctuated through episodes of global extinction but never crossed the zero line, not for one millisecond. DNA has been working all this time, without an hour of vacation or even a moment of pause to remember the extinct brethren of a billion dead branches shed from an ever growing tree of life.

When Protagoras, speaking inclusively despite the standard translation, defined "man" as "the measure of all things," he captured the ambivalence of our feelings and intellect in his implied contrast of diametrically opposite interpretations: the expansion of humanism versus the parochialism of limitation. Eternity and infinity lie too far from the unavoidable standard of our own bodies to secure our comprehension, but life's continuity stands right at the outer border of ultimate fascination: just close enough for intelligibility by the measure of our bodily size and earthly time but sufficiently far away to inspire maximal awe.

Moreover, we can bring this largest knowable scale further into the circle of our comprehension by comparing the macrocosm of life's tree to the microcosm of our family's genealogy. Our affinity for evolution must originate from the same internal chords of emotion and fascination that drive so many people to trace their bloodlines with such diligence and detail. I do not pretend to know why the documentation of unbroken heredity through generations of forebears brings us so swiftly to tears and to such a secure sense of rightness, definition, membership, and meaning. I simply accept the primal emotional power we feel