Chapter One

The Evolution of Purpose

We evolved. We have only to look at the pouting face of a young chimpanzee to laugh at its reflection of ourselves. We know that more than 98 percent of our genes are shared with the chimpanzee, but we feel the kinship directly when the furry baby puts up its arms to be held.

Still, we are very reluctant to credit chimps with that most human quality, a sense of purpose. Surely no ape ever asked why it is here, what it evolved for ? Somewhere in the progress from ape to human, the first philosopher appeared. Every human society we know of has asked, and offered some answer to, the question "What for?" Chimps do not puzzle over that question, but, strangely, they help us confront an even more abstruse one: Why do we ask what for? Why do we feel that the world and our own existence must have a purpose?

When we were evolving human minds, the environment posed many challenges. We had to find, recognize, and remember foods that were growing erratically about the savanna. We invented tools to smash nuts, dig for roots, and hurl at prey. We dodged saber-tooth cats and competed for food with troops of gigantic baboons. However, similar challenges confronted other primates. All animals have predators, competitors, and prey. What was different for us?

The difference was that we lived in social groups of creatures just about as smart as ourselves. Our minds were honed in a social nexus generation by generation. We outsmarted rivals of our own sex by forming alliances with our friends against other networks of allies. Both males and females chose mates from a range of suitors. One way to be chosen was to be smart--smart at providing food, or distracting rivals, or wooing with primeval forms of music and rhetoric. Endearments--and insults--may have been among the earliest parts of speech. At some much disputed period we developed rights and commitments to particular mates, and affection and obligations toward both of our parents. Juggling relationships is the stuff of soap operas, but it made us smarter. Captive chimpanzees and bonobos love watching soap operas.

The pressure of others' intelligence drove our minds in a forward spiral. We gained advantages for ourselves and our children whenever we could predict the actions of others, both friends and foes. The efficient way to predict a live creature's actions is not to do abstract, billiard-ball deductions about where it came from or which way it is headed but to ask what the chimp or dog or baby wants . In the long (Darwinian) run, we all want to survive and reproduce. All animals have developed a baroque collection of subroutines en route to this end. I want to eat a carrot or a chocolate chip cookie that is tempting me now, not because it builds vitamin-rich tissue or energy to bring up the kids. We enjoy sex for its own sake, now, not to make a baby nine months down the line.

A primate does not need to go beyond these immediate subroutines to sense that a rival "wants" to dig up the root I spotted, she "wants" to take the last cookie on the tray, she "wants" to cuddle up to the male I had my eye on. If a more subtle ape sees these things a little more clearly than the next ape, she may be a little more likely to turn the tables and gain her own ends. Then, somewhere along the trail of the generations, she becomes able to detach herself enough to think of her own behavior in such terms. At this point we drop the scare quotes; these are real goals, not just felt desires. Eventually the goals become Machiavellianly explicit: "He'll never see what I'm up to behind the bushes," or "I'll encourage her to grab that gooey cookie so he will see that I am pure but generous and she is a selfish slob," or "OK, I'll bite the cookie with gusto, and eye him over the top so he'll imagine enjoying other pleasures."

The chimp and its society tell us that our minds are shaped by the world of our ancestors. In that world, other ape-people were filled with purposes. From the purposefulness of our fellow humans we leap to the assumption that everything has a purpose. Richard Dawkins says, "It is almost as if the human mind has been designed to misunderstand Darwin." Too right. We have evolved a social primate's mind that looks for purpose in everything.

The thought that nature itself might have no purpose was anguish in the nineteenth century, as it is to many today. The extinction of species raised the sacrilegious prospect of humanity itself as one more transient life form. Would we too be cast off by nature's indifference? Alfred, Lord Tennyson distilled that anguish in his elegy In Memoriam , which became so famous that even Queen Victoria kept it by her bedside. Man, last of nature's creations, so full of hope and splendid purpose,

Who trusted God was love indeed

And love Creation's final law--

Tho' Nature, red in tooth and claw

With ravine, shriek'd against his creed--

even Man might become shards of fossil bone, finally left to

Be blown about the desert dust,

Or seal'd within the iron hills.

Darwin's Decision

Charles Darwin hesitated for twenty years before publishing his theory of evolution through natural selection in 1859. He was not idle, nor indifferent, nor unconscious. His early notebooks spelled out the whole theory in 1838. He occupied eight of the intervening years with prodigious labor on the anatomy of barnacles. Barnacles!--with the theory that would change humanity's view of itself already written, with instructions to publish if he should die. He hid his blasphemous idea in part because of the anguish it would cause to believers, including his own wife, if he could successfully explain the evolution of living forms without recourse to divine purpose. He also hid through fear of revenge on his social position and scientific respect.

Then in 1858 Alfred Russel Wallace wrote a short letter from Indonesia outlining the principle of natural selection in a few pages. It finally catapulted Darwin into publishing a 500-page "preliminary sketch" of evidence for his theory.

On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life was far from the first book to propose the evolution of one form from another. Charles Darwin's grandfather, Erasmus Darwin, had done so, as had the French naturalist Lamarck and the Scot Robert Chambers. Evolution was in the air, along with the innovations and extinctions it implied. Tennyson's poem was published nine years before the Origin of Species . What Darwin did was give evolution a mechanism , a means of arriving at the diversity of living and fossil creatures without the intervention of conscious purpose. The philosopher Daniel Dennett calls this the difference between skyhooks and cranes. Evolution was no threat if a benevolent deity leaned over from on high with a skyhook to haul life upward for his own divine ends. When Darwin proposed instead a kind of crane, a physical means of building life's complexity from the ground below, it was horrifying.

Darwin was a proper Victorian gentleman. He aspired to the respect of the illustrious scientists who ran the Geological Society of London, men who damned Lamarck for his "gross and filthy" views on evolution. Biology in Darwin's time was almost exclusively natural history--gentleman's beetle collecting, the hobby that sent Darwin cycling round the countryside when he was supposed to be studying for the ministry at Cambridge University. Gentlemen belonged to the established Church of England. Their God personally designed every single species of beetle. As a theology student, Darwin read and reread Paley's Natural Theology, or Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature . Paley said that if, by chance, he kicked a stone on his path, he might assume it had lain there forever. If, however, he found a watch, he would know at once that someone had made it, and that its parts were put together for a purpose. Plants and animals, in turn, are far more complex and more beautiful than any watch. Therefore they must have arisen by divine design, not mere chance. Paley's God, the God of the scientific establishment, shared a major strand of Darwin's own character--delight in every fact and facet of living nature.

Darwin was not born a grand old man with a beard. During the voyage of the Beagle he rejoiced with a young man's gusto in riding off through South America toward the Andes in pursuit of discoveries (though he never got over being seasick on shipboard). When he came home to London he was a bachelor-about-town, seeing much of his brother Erasmus and Erasmus's friends, especially the literary lioness Harriet Martineau. Martineau overcame the handicaps of being female, single, ugly, and deaf to write immensely popular political fiction. One of her soap-opera morality tales explained Thomas Malthus's principle that human population grows at compound interest unless checked by famine, war, disease, or moral restraint. Meanwhile, mobs rioted in the streets against the Malthus-inspired New Poor Law of 1834, which sent the destitute to workhouses made as harsh as possible to discourage paupers from seeking aid. Parliament justified the new Poor Law by quoting Malthus: the superfluous poor should be checked from reproducing.

The idea of the theory of natural selection came to Darwin when he was reading Malthus "for amusement." He doubtless discussed Malthus's ideas with Martineau and others of their London circle. Their background, like his own family's, was mercantile, not aristocratic, These entrepreneurs dealt in the laws of gravity, steam power, and compound banking interest as well as compound population growth. Darwin became an increasingly explicit atheist. He turned from the God who sculpted each beetle carapace to the abstract grandeur of universal law.

Evolution itself called to the hopes of the rioting mob. The idea that species could arise one from another appealed to a working-class audience--men who went to public lectures and night schools in the hope of self-improvement. If species themselves were mutable, so might a working-class Englishman hope to rise in station. If the history of life was one long march of progress, even laborers, or society itself, could expect to advance toward a better life. This doctrine was revolting to the wealthy classes, with their vested interest in the status quo--revolting, and revolutionary. Darwin's friends repeatedly warned him that espousing evolutionary progress would ally him with riffraff that the gentleman scientists despised.

These three strands came together in the final theory: awe and delight at nature's diversity, explanation how that diversity of nature arose through a grand and simple law, and understanding that the law of natural selection at last explained evolution of new species and indeed the progress of life itself.

Natural selection is simple. Richard Dawkins remarks it is so simple that if we did not have a deep-seated distrust of mechanism we could hardly have waited millennia to come up with the idea. Indeed, Aristotle almost did, proposing that perhaps all possible forms had once existed, including monsters like "man-faced oxen." Then only those that were best fitted for life survived. Aristotle then veered away, seeing no way to produce the variety of such monsters in the first place. He concluded that all parts of living organisms arose both through mechanical "prior cause" and for a purpose "as leaves exist in order to shelter the fruit."

After twenty years of labor, Darwin could summarize the "prior cause," the actual mechanism of natural selection, in one paragraph. He kept the last paragraph of his masterpiece unchanged through all successive editions of the Origin :

It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance, which is almost implied by reproduction; Variability from the direct and indirect action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

Darwin's "Laws Acting Around Us"

Self-maintenance, growth, and reproduction.The most fundamental property of life is active self-maintenance. Living things work to stay alive. They take in nourishment, repair themselves, and grow. But as soon as some accident, predator, or disease destroys a living thing, it is gone. If it has left no descendants, its genetic information is gone. If it has influenced no others, its ideas are gone. Working to stay alive can work only for a finite time. Leaving extra copies of oneself guards against such total annihilation. The second fundamental property of life, then, is reproduction. Life began, by definition, when the first chemical molecules that could make copies of themselves condensed from the primordial ooze.

This fact that living things have the potential to grow and reproduce is what is wrong with the Gaia hypothesis that Earth itself is a living organism. Granted, Earth in some ways seems extraordinarily like a self-regulating system, like a living thing. James Lovelock, who proposed the idea in 1979, showed that marine algae produce a gas called dimethyl sulfate, which promotes cloud formation, partially regulating Earth's temperature. Most Darwinians thought this could hardly be selected for in evolution: what is the profit in it for the algal genes? However, if algae blooms are massive clones, then promoting clouds would allow their own genes to disperse--a reproductive advantage for the makers of the weather. Perhaps the self-interest of algae stabilizes temperature and climate in such a way that the rest of us can survive.

Yet, so far as we know there is only one Earth, which neither grows nor reproduces. Even though the parts look suspiciously well coordinated, we still know of no mechanism that produces complex natural organization on the scale of the biosphere itself. Et could be that the coordination is a case of observations in search of a theory, much like the data of continental drift, which were not believed until people recognized the mechanism of sea-floor spreading and plate tectonics. Or it could be that the notion of Earth as organism just is not viable. Meantime, the simplest amoeba or bacterium has the first properties of life: self-maintenance, growth, and reproduction.

Inheritance. Darwin talked about reproduction not of genes but of parents' form and behavior. He did not know about genes, chromosomes, DNA. However, it was obvious to Darwin that natural selection could not work unless offspring inherited tendencies to develop the traits that made their parents successful.

Darwin worried about the problem of blending inheritance. Supposing, he wrote, that a white man were shipwrecked on an island with a black population. His offspring would be mixed, their offspring more so. If the genetic information were blended and dispersed, like a drop of water added to a bottle of ink, it is impossible that in some future generation a child would reassemble all the "white" genes and look like her shipwrecked ancestor. Suppose, however, that genetic information is not blended but rather the genes are shuffled and dealt like cards in a game of bridge. It is statistically no more unlikely for all the hearts to fall together than any other of the possible sequences of thirteen cards. With enough shuffling, children in a limited population could partially or wholly recreate some ancestral genetic pattern, as, at times, the offspring of a white South African couple show black background long since successfully denied in their forebears' past. This is called particulate inheritance. In the first edition of the Origin Darwin rejected blending inheritance, but eventually even he lost faith in particulate inheritance and watered down later editions. Not until the rediscovery of Gregor Mendel's work on genetics was blending inheritance finally put to rest.

Mendel was an Austrian monk, a high school teacher, and a biologist who published just two papers in 1866 on the outcome of crossing peas. He annotated his copies of Darwin's works and saw how his own experiment fit with natural selection. He focused on a few characteristics: tall plants versus short plants, yellow versus green peas, wrinkled peas versus smooth--seven traits in all. He found that first-generation offspring all resembled one parent, the "dominant" one for each characteristic. In the second generation, they came out in the ratio of three to one, where the odd one inherited two recessive factors for the trait. Of the three with dominant characteristics, one had two dominant factors and the other two had a dominant and a recessive, but the dominant factor determined the look of the adult plant. The important point, to Mendel, was that the traits segregated independently from one another. He postulated that whatever factors produced the traits were sorting digitally and independently, like shuffled cards, not blending like a liquid.

Very few characteristics in humans are as genetically simple as Mendel's pea plants. Our major blood types, A, B, AB, O, are based on single gene differences, but not much else is. Sex begins with a single gene difference, but sex is one of the very few traits where we have distinct castes: most people are either male or female. Most of the interesting traits, such as intelligence, involve an astronomically complex interaction of many genes with the environment. The basic principle, though, is that genes are discrete, particulate. That means that the information to rebuild parents' characteristics can pass intact from generation to generation.

Variability. For natural selection to work, individuals must differ within a population. If the line of descent consisted of perfect clones, no individual would be genetically better adapted to its environment than any other. Some would be lucky enough to survive while others died, but this produces no change in the genetic stock. Darwin pointed out that in fact puppies differ even within one litter; fancy show pigeons differ within an inbred strain. Evolution is not about the perpetuation of some static ideal type but about the differences and innovations that give some few individuals an edge in the struggle for life.

Darwin equivocated between what Ernst Mayr calls "hard" and "soft" inheritance. Hard inheritance is what we now know to happen: Mendel's mutations occur randomly within the genome, and changes in the genome are transmitted to offspring. Environmental conditions that reach the genes are random mutagens, like ultraviolet light, mustard gas, atomic radiation, which hit the DNA like a scatter of shotgun pellets. Soft inheritance instead would allow external conditions to shape particular heritable factors, both directly, indirectly through increasing variability, and above all, through use and disuse of parts of the body--the so-called Lamarckian heresy. Lamarck's notion was that the giraffe, stretching its neck to reach tall trees, somehow stretched the neck of its unborn young. Hard inheritance says, instead, that taller giraffes swiped off leaves from tall trees out of reach of their shorter kin, and so survived to better sire and bear giraffe calves who inherited the parents' gangly genes.

It remained for August Weismann, at the end of the nineteenth century, to sort the story out and to place hard inheritance on a firm theoretical and empirical basis. He pointed out that many adaptations could not have arisen from habit or use during animals' lives--they are too complex, or their benefit happens after the animal is dead, or they produce highly adapted nonreproductives, such as the sterile castes of insects. Among a wealth of other observations and experiments, Weismann is remembered today for cutting off the tails of generations of mice. The distant offspring grew tails as long as ever, in spite of their parents' "disuse" of any tail. Only when Weismann interbred the naturally (genetically) short-tailed mice of his stock, generation after generation, did the descendants eventually inherit genes for puny tails. We now imagine only a mad farmer's wife would carry out this procedure, but Weismann recalled how he faced critics who believed that puppy dogs did indeed inherit their mothers' docked tails, and that "even students' fencing scars were said to have been occasionally transmitted to their sons, though happily not their daughters."

Josef Stalin tested out Weismann's findings on a grand scale. Stalin had power to experiment on a whole nation's bread and borscht and vodka. The biologist Lysenko launched an attack on a flourishing Russian school of genetics in 1936, achieved full triumph in 1948, and did not fall from power until 1965. Lysenko argued that crops could acquire the habit of growing well for Communism. They should be fertilized and tilled, just as peasants should receive political education. It was immoral, according to Lysenko and Stalin, to save only elite seeds to sow. The crops' genetic stocks declined through lack of selection, playing a part in the collapse of Soviet agriculture, while Soviet evolutionary biology lost two decades of growth, as "hard" geneticists were fired, imprisoned, or killed.

A ratio of increase so high as to lead to a struggle for life. This is Malthus's principle that every organism is capable of reproducing by exponential growth. This means every species can produce more offspring than have room to live in a finite habitat. Malthus's principle, acting on inherited variability, is the key to natural selection. If many more offspring are born than can possibly survive, those less well adapted to their environment will automatically be culled. In the same way, a purposeful human breeder produces new strains by saving only a few of each generation and culls those that do not measure up to the breeder's ideal. Malthus's principle is not so much about life as about the inevitability of death--the myriad shadowy might-have-beens.

Natural selection. The sum of all these elements gives the mechanism of natural selection, "entailing divergence of character and the extinction of less-improved forms." The actual divergence of character comes from tracking the environment. As a few individuals of a litter, or a species, are genetically better at coping with the environment, they drive their competitors to extinction. In this way the species as a whole is "improved" in relation to its environment, but through a wholly mechanical means, and through the self-interest of each organism in its own survival . There is no judgment about what constitutes "improvement." A parasitic barnacle which jettisons all adult organs except the gonads and feeds by sucking nutrients from a crab, its host, is improved if it survives to reproduce.

The War of Nature

Even in this triumphant final paragraph Darwin talks of the war of nature, of famine and death. Competition for him includes direct competition, as of two plants sucking water and nutrients from each other's roots, racing up toward the sun' the winner shades and shrivels the weaker. He also speaks of competition against the onslaught of the environment' to be the plant that can best stand the desiccation of the desert edge, or the frosts of winter. Competition, unthinking cruelty, the driving of others to death or extinction are the basis of natural selection of the few which survive.

Yes, it does sound a lot like nineteenth-century capitalism. Competitive individuality is the basis of natural selection, and of that brand of economics which believes in a free market, an idealization of individuality rarely or never found among actual human transactions. Humans recognize other individuals and cooperate, or at least cut deals, with those they know. It turns out that the major advances in evolution also involve cooperation.

What do we mean by an advance? A very simple yardstick is size. Single cells are bigger than bacteria, multicellular bodies are bigger than single cells; societies are bigger than single bodies. Size usually implies complexity, as the number of different interacting parts grows from level to level. Each level involves a community of the simpler individuals of the level below.

Cells originated as a community of originally free-living bacteria. Bodies are communities of mutually supportive cells. Societies, obviously, are a somewhat coordinated community of individuals. The great transitions in evolution have produced ever larger matrices of cooperation. In this sense there has been a genuine directionality in evolution, toward more and more complex interconnection. If we wish to think that complexity is indeed an improvement, we may call it progress.

How does such cooperation arise from the fierce competition of natural selection? Cooperation arises between biological entities much as it arises between people. It is advantageous to both partners, or else one imposes itself on another and forces the second to obey. Natural selection is built on individual advantage. The agony or futility of the crab being sucked of its vital juices by the parasitic barnacle, the human being in spasmodic dehydration by cholera bacilli, or the rabbit skewered by an eagle's talons are unjudgmentally produced by the blind forces selecting for individual survival of barnacle, bacillus, eagle. But love, altruism, self-sacrifice are also real and have also evolved and survived, not just in ourselves. The lesson of Darwin's war of nature is not that unfettered selfishness is somehow good but that by understanding the war of nature we can also understand kindness and love in the natural world.

From So Simple a Beginning

Darwin surmised that present living things stem not from a few forms but from one. All of us construct our bodies using the same genetic code. The code has long been considered highly arbitrary, what Francis Crick called a "frozen accident." Recently, biologists are figuring out some of the chemical constraints that may have shaped the code's early evolution, and also finding that the code is extraordinarily efficient, more efficent than the artificial permutations that we can now jam into it, or simulate by computers. This means that the code itself evolved over time. Perhaps the ancestor who had the code we all use now was the fittest survivor among many early life forms, or perhaps those simple life forms exchanged components among themselves, and jointly converged on the pattern of our universal ancestor, the progenitor of you, me, the earthworm under your foot, the pigeon over your head, and the cold virus inside you.

Some still consider natural selection only a hypothesis to be tested, although even the Pope now concedes that it is a "theory of vast explanatory power." Darwin claimed even more: that natural selection would prove to be a universal law of nature, an organizing principle like Isaac Newton's law of gravity. "There is grandeur in this view of life," he wrote, in awe of nature as majestically simple, whose universal laws explain the swarming embodiments of reality. In the end, Darwin was buried in Westminster Abbey, near the monument to Newton, England's hero of science.

Paley's test of the watch on the moor is trivial compared to the complexity of the merest beetle, even the merest cell. The DNA in each cell of a person contains as much information as an encyclopedia. And that is only the blueprint--the code to produce the interacting proteins that build the scaffolding that builds the structure. The final structure of a living thing is as much more complicated than its DNA as a cathedral is more complicated than the architect's blueprint. How can such things arise without a planned design?

The key is not just natural selection but cumulative selection. Each step of survival does not start from a blank and random slate but from a previous parental blueprint already evolved over millions of generations. The embryo does not construct itself from scratch, like a tornado in a junkyard somehow producing a Boeing 747, to use Richard Dawkins's analogy. Instead, each change is a minor tweaking of a previous body plan. A few changes are larger--repeating a body segment, for instance--but it is extraordinarily rare that individuals carrying large single steps of modification survive. Dennett's "crane" building up from below is building itself, on itself. The mechanism of reproduction, inheritance, variation, struggle for life is enough, when building on what went before.

Darwin's own test case was the evolution of the eye in all its precision. Generations of scientists have now traced the evolution of eyes. Each step was selected in turn, from the first light-sensitive pigment spot that might have registered the shadow of a swimming predator, up to the single-lens reflex of ourselves or, independently, the octopus, or the very different array of compound and simple eyes that a jumping spider uses to target its prey. It seems that eyes have evolved independently at least thirty times over. But even eyes are jettisoned when they are no longer useful. The mole rat's remnant eye is buried beneath skin and fur. Its brain circuits are rerouted to deal with the tingling of its vibrissae and to decode the sound of messages sent by other mole rats thumping their skulls against the roofs of underground tunnels.

The same principle explains a great deal of the fine tuning in nature: enough of an enzyme, but not too much, fast enough legs to outrun the predator most of the time, but not legs like the cheetah, unless you are a cheetah. And cumulative selection does fine in explaining the presence, and even the absence, of the amazing eye.

Forms Most Beautiful and Most Wonderful

The entangled bank of "most beautiful and most wonderful" forms does not become simple and drab just because it has evolved through the fixed law of natural selection rather than divine intervention. Darwin certainly did not think so. Once he had found the mechanism of evolution, he did not feel there was no more to see or to say. He led a life of perpetual fascination with natural forms and behaviors: earthworms, barnacles, orchids, pigeons, peoples. His metaphors inspired the great literary minds of his time, and Darwin's image of the entangled bank remains with us today.

The idea that science reduces the wonder of nature to sterile abstraction is the fallacy of reductionism. Nature is not "nothing but" a DNA blueprint, or atoms, or quarks. A Gothic cathedral is a pile of stones, pressing down upon one another according to the fixed law of gravity, with the addition of a design inspired by the architect. A Madagascar landscape of pinnacle karst--knife-tipped needles of limestone soaring 150 feet into the air--is as breathtaking as a Gothic cathedral. It too is a pile of stone, inspiring the beholder but shaped only by gravity and gravity's handmaid, erosion.

The idea that either cathedral or karst pinnacles are "nothing but" stone leaves out their form. A full description must include the architecture. The shape of a thing is no mystical essence, but it is not reducible to the materials which take that shape. A white sifaka, one of the glorious tribe of Madagascar lemurs, which dances over the ground and springs fifteen feet at a bound between branches and makes its home in hanging gardens among the pinnacles, is not "nothing but" molecules. Neither is it molecules imbued with some vital fluid of mystic life force. It is an architecture of molecules shaped by natural selection, just as the pinnacles are shaped by erosion. It is a sifaka.

Does wonder depend on ignorance? Is science merely Edgar Allan Poe's "vulture, whose wings are dull realities"? Or are we allowed to ask how the rain grooved the pinnacles, how the sifaka's wide eyes detect the predator, the nerves' electricity signals the leap, and the muscles contract as it springs in the air? Can we see how swooping hawks and the ravenous fossa (a giant, cat-clawed mongoose) provided the selection pressure that led to lemurs who leaped in time to survive? Does the sifaka become less wonderful if we imagine the layers of complexity in muscle and nerve and gene?

Our wonder itself is a product of natural selection. The emotions of wonder and of beauty evolved. They are an integral part of every human mind. Does that mean they are "nothing but" chemical products, like sugar and vitriol? The feelings, like the sifaka's leap, exist. Even if we succeed in understanding how they are produced, explanation does not explain them away.

This brings us back to the beginning. Evolutionary explanation gives us clues why we see the world in terms of purpose. Natural selection of bodies that survive refined the brains of social primates into minds that want consciously to survive, that think in terms of purposes. We see purpose in our comrades, in other living creatures, even in lifelike manifestations such as thunderstorms and cars and computers.

We have no proof whether there is a larger purpose in the universe or not--or perhaps it is fairer to say that some of us see no proof, while many others do. We may or may not have free will to choose between the courses of action offered up in the conscious part of our minds. All that is a larger metaphysics, an argument which has lasted three thousand years or so and will likely continue. Perhaps most can agree, though, that our own conscious purposes are real. A biological explanation of how the brain works, how the nerves offer up thoughts on our mental screen, does not deny the thoughts are there. That would be like saying if we understand the nerves and muscles and evolutionary history of the sifaka's leap, then suddenly the poor beast can't jump.

Our human sense of purpose is a product of our biological heritage; it now is changing the biology of the world around.