October 10, 2008

Three Facets of Evolution

I'd like to put up this excellent short piece by the late Stephen Jay Gould, the renowned palaeontologist and evolutionary biologist. It was originally published in How Things Are: A Science Toolkit for the Mind by John & Katinka Brockman (1996), and it outlines evolution theory and the bare basics of how to deal with some of the current controversies.


Three Facets of Evolution

§ - What Evolution Is Not.

Of all the fundamental concepts in the life sciences, evolution is both the most important and the most widely misunderstood. Since we often grasp a subject best by recognising what it isn't, and what it cannot do, we should begin with some disclaimers, acknowledging for science what G. K. Chesterton considered so important for the humanities: 'Art is limitation; the essence of every picture is the frame.'

First, neither evolution, nor any science, can access the subject of ultimate origins and ethical meanings. (Science, as an enterprise, tries to discover and explain the phenomena and regularities of the empirical world, under the assumption that natural laws are uniform in space and time. This restriction places an endless world of fascination within the 'picture'; most subjects thus relegated to the 'frame' are unanswerable in any case.) Thus, evolution is not the study of life's ultimate origin in the universe or of life's intrinsic significance among nature's objects; these questions are philosophical (or theological) and do not fall within the purview of science. (I also suspect that they have no universally satisfactory answers, but this is another subject for another time.) This point is important because zealous fundamentalists, masquerading as 'scientific creationists,' claim that creation must be equated with evolution, and be given equal time in schools, because both are equally 'religious' in dealing with ultimate unknowns. In fact, evolution does not treat such subjects at all, and thus remains fully scientific.

Second, evolution has been saddled with a suite of concepts and meanings that represent long-standing Western social prejudices and psychological hopes, rather than any account of nature's factuality. Such 'baggage' may be unavoidable for any field so closely allied with such deep human concerns (see Part 3 of this statement), but this strong social overlay has prevented us from truly completing Darwin's revolution. Most pernicious and constraining among these prejudices is the concept of progress, the idea that evolution possesses a driving force of manifests an overarching trend towards increasing complexity, better biomechanical design, bigger brains, or some other parochial definition of progress centered upon a long-standing human desire to place ourselves atop nature's pile - and thereby assert a natural right to rule and exploit our planet.

Evolution, in Darwin's formation, is adaptation to changing local environments, not universal 'progress.' A lineage of elephants that evolves a heavier coating of hair to become a woolly mammoth as the ice sheets advance does not become a superior elephant in any general sense, but just an elephant better adapted to local conditions of increasing cold. For every species that does become more complex as an adaptation to its own environment, look for parasites (often several species) living within its body - for parasites are usually greatly simplified in anatomy compared with their freeliving ancestors, yet these parasites are as well adapted to the internal environment of their host as the host has evolved to match the needs of its external environment.

§ What Evolution Is.

In its minimalist, 'bare bones' formulation, evolution is a simple idea with a remarkable range of implications. The basic claim includes two linked statements that provide rationales for the two central disciplines of natural history: taxonomy (or the order of relationships among organisms), and palaeontology (or the history of life). Evolution means (1) that all organisms are related by ties of genealogy or descent from common ancestry along the branching patterns of life's tree, and (2) that lineages alter their form and diversity through time by a natural process of change - 'descent with modification' in Darwin's chosen phrase. This simple, yet profound, insight immediately answers the great biological question of the ages: What is the basis for the 'natural system' of relationships among organisms (cats closer to dogs than to lizards; all vertebrates closer to each other than any to an insect - a fact well appreciated, and regarded as both wonderful and mysterious, long before evolution provided the reason). Previous explanations were unsatisfactory because they were either untestable (God's creative hand making each species by fiat, with taxonomic relationships representing the order of divine thought), or arcane and complex (species as natural places, like chemical elements in the periodic table, for the arrangement of organic matter). Evolution's explanation for the natural system is so stunningly simple: Relationship is genealogy; humans are like apes because we share such a recent common ancestor. The taxonomic order is a record of history.

But the basic fact of genealogy and change - descent with modification - is not enough to characterise evolution as a science. For science has two missions: (1) to record and discover the factual state of the empirical world, and (2) to devise and test explanations for why the world works as it does. Genealogy and change only represent the solution to this first goal - a description of the fact of evolution. We also need to know the mechanism by which evolutionary change occurs - the second goal of explaining the causes of descent with modification. Darwin proposed the most famous and best-documented mechanism for change in the principle that he named 'natural selection.'

The fact of evolution is as well documented as anything we know in science - as secure as our conviction that Earth revolves about the sun, and not vice versa. The mechanism of evolution remains a subject of exciting controversy - and science is most lively and fruitful when engaged in fundamental debates about the causes of well-documented facts. Darwin's natural selection has been affirmed, in studies both copious and elegant, as a powerful mechanism, particularly in evolving the adaptations of organisms to their local environments - what Darwin called 'that perfection of structure and coadaptation which most justly excites our admiration.' But the broad-scale history of life includes other phenomena that may require different kinds of causes as well (potentially random effects, for example, in another fundamental determinant of life's pattern - which groups live, and which die, in episodes of catastrophic extinction).

§ Why Should We Care?

The deepest, in-the-gut, answer to the question lies in the human psyche, and for reasons that I cannot begin to fathom. We are fascinated by physical ties of ancestry; we feel that we will understand ourselves better, know who we are in some fundamental sense, when we trace the sources of our descent. We haunt graveyards and parish records; we pore over family Bibles and search out elderly relatives, all to fill in the blanks on our family tree. Evolution is this same phenomenon on a much more inclusive scale - roots writ large. Evolution is the family tree of our races, species, and lineages - not just of our little, local surname. Evolution answers, insofar as science can address such questions at all, the troubling and fascinating issues of 'Who are we?' 'To which other creatures are we related, and how?' 'What is the history of our interdependency with the natural world?' 'Why are we here at all?'

Beyond this, I think that the importance of evolution in human thought is best captured in a famous statement by Sigmund Freud, who observed, with wry and telling irony, that all great scientific revolutions have but one feature in common: the casting of human arrogance off one pedestal after another of previous convictions about our ruling capacity in the universe. Freud mentions three such revolutions: the Copernican, for moving our home from center stage in a small universe to a tiny peripheral hunk of rock amid inconceivable vastness; the Darwinian, for 'relegating us to descent from an animal world'; and (in one of the least modest statements of intellectual history) his own, for discovering the unconscious and illustrating the nonrationality of the human mind. What can be more humbling, and therefore more liberating, than a transition from viewing ourselves as 'just a little lower than the angels,' the created rulers of nature, made in God's image to shape and subdue the earth - to the knowledge that we are not only natural products of a universal process of descent with modification (and thus kin to all other creatures), but also a small, late-blooming, and ultimately transient twig on the copiously arborescent tree of life, and not the foreordained summit of a ladder of progress. Shake complacent certainty, and kindle the fire of intellect.

No comments:

Post a Comment