One of the most sobering lessons neuroscience has to teach us is that we are at the mercy of our brains.

But then again, that statement is not entirely accurate. It is infused with a subtle taint of dualism, and dualism is a doctrine that I, as an atheist and thus a strict materialist, naturally reject. To say that we are at the mercy of our brains implies that there is some "we" - some essence of self, some soul-stuff, some deeper wellspring of identity - that can be viewed as separate from, though affected by, our brains. Of course there is no such thing - we are our brains. Their workings produce our thoughts, our minds, our consciousness; and marvelous instruments though they are, ultimately they are material things, vulnerable to all the flaws and vicissitudes inherent in matter.

This conclusion is only common sense, and its most obvious symptom is the way our rational minds are so often overruled by our emotions and so rarely the other way around. Our moods govern our decisions and influence our judgment in a way that dispassionate logic almost never can. How many people, in the heat of an angry moment, have said or done something they would later sorely regret? How many people have ever been paralyzed by fear when alone in the dark, despite the rational knowledge that there's nothing hiding in that corner? How many people have ever been driven to distraction by a hopeless crush, whether romantic or sexual, on a person they know they could never have but couldn't stop dreaming about anyway?

These experiences are common to all human beings. And though outwardly they may have very different effects, in a fundamental way they are all alike: though we may understand our emotions intellectually, though we may rationally appreciate how they affect our behavior, when they are upon us we are powerless to resist them.

The experience that gave rise to this essay happened to me several weeks ago. I was alone in my apartment on a chilly fall day, late in the afternoon, and for no reason that I was aware of, I suddenly began to feel lonely - isolated from friends and loved ones, overwhelmed with work, weighed down by all the everyday troubles brooding on my mind. But none of these things were the cause of this sudden melancholy, though they contributed to it once it had begun; it grew seemingly by itself, not in response to any external events.

Though there's no reliable cure for this kind of depression once it's come on, I know from experience that a sure way to make it worse is to sit around doing nothing. Going for a walk always helps me to clear my head and put my thoughts in order, and often that's enough to improve my mood. In any event, I felt a desire for human companionship, not necessarily to talk to anyone, but simply to be around people. I took my coat and notepad, checked the schedule, and caught the next bus to campus.

It was early evening when I arrived, and the sun was just beginning to set. Almost immediately, I was struck by how beautiful the sky was. A broad river of clouds stretched across the heavens; in the west it was soft violet, its edges outlined with pink and orange in the waning gold of the sun's last light. As the river meandered into the east, it widened and faded into a string of blue, an archipelago of misty floating islands. There were other colors as well, shadowing the more visible ones: ripples of red and purple, faded pale shades of tan, and in the far east, beyond the blue, smoky suggestions of almost invisible white form as if from mountains beyond the limits of sight. It was a tableau of breathtaking vastness and beauty, a panorama that would put the work of the greatest artist to shame.

Wanting to get a better look, I climbed to the top of a tall, grassy rise behind the university concert hall. This was several days before an open-air concert to be held in memorial of September 11, and an ascending framework of steel bleachers had been set up on the hill. The top row of these provided the vantage point I wanted, and I sat there for a time, doing my best to write something that captured the beauty of the evening sky. It was an impossible goal, of course. Words were not enough to depict the complexity of shape or describe the vast scale, with distance and size unknowable in the endless blue, and the mind of man has not invented names for all the colors that were visible there. It is in these situations, I thought, when faced with the grand ineffable majesty of nature, that we run up against the limitations of language. At such times I can appreciate the claim of Zen Buddhist mystics that mere words are inadequate to communicate the nature of ultimate reality.

The colors of sunset never last long, and indeed the scene was slowly, almost imperceptibly, softening and fading even as I sat and watched it. I felt better, but not entirely.

As the sky edged over into late evening, I happened to glance over to one side, out across the campus library plaza. There were not many people there, but my gaze fell on a couple, sitting on a bench on a nearby grassy hilltop, she in red, he in black. They were kissing, oblivious to everyone but each other, and a thought struck me: whatever had happened in the past and whatever the future held, it didn't matter. Together, for that one perfect moment, they were happy.

And as if that realization had been a spark that had kindled a flame within me, I suddenly felt reawakened, my melancholy mood banished in an instant. As trivial a thing as it was, it had completely reversed my frame of mind. I never knew the couple, but if they ever read this, I would like to thank them for giving me what turned out to be a perfect evening after all.

What is the point of this story? Simply stated, it is this: Even in the midst of this dark, downtrodden world of meaningless suffering, there are still reasons to take pleasure in life, wellsprings of happiness. In fact, there are many of these, but most of them are so mundane, so familiar, that they are easy to overlook. I did once, and it took an unexpected spell of depression to remind me to see again. When you are in darkness, even the smallest gleam of light seems far brighter by comparison. On that day, I realized anew that the secret to life is to take pleasure in the small things - to find beauty in the mundane.

So what are some of these mundane sources of beauty? This atheist finds them in two main categories: in the small acts of human kindness and in the baroque beauty of the natural world. Both these things are all around us, freely available for those who would appreciate them. Consider:

• Have you ever stood at twilight and watched steam or smoke rise from a chimney against the darkening sky, or watched your breath cloud and spiral away in freezing cold air? From the interaction of just a few simple rules, the infinitely complex phenomenon of turbulence builds up, a restless, swirling fluid flow that so far humanity's best minds have not been able to fully understand.

• How many stories have you read or listened to recently? How many books have you read, how many plays have you seen? We human beings are storytellers - we have always been, since we were hunters gathered around fires in the dark. It is one of the most marvelous gifts of intelligence and an unsurpassed way to fill our lives with meaning and beauty. In addition to simply entertaining, stories can teach us lessons, instill in us purpose, transport us to places we have never been, and preserve the humor and wisdom of our greatest minds over the ages. Our books and libraries are the crowning triumph and the glory of our civilization.

• Have you ever awakened early to see the sunrise? It begins with the dark before the dawn, that quiet hour when all the world is asleep. By the faintest of degrees, the sky in the west gradually lightens from midnight blue to pale, milky grey, and the western horizon pearls. Shadows fade and dew begins to sparkle as the soft light becomes a thin line, then an arc, then a brilliant sunburst of bright white light along the edge of the Earth. The sky lightens further, from washed-out grey to pale pink, and whatever wisps of cirrus cloud there may be glow silver, rose and orange in the fire of the rising sun. How beautiful and peaceful are those hours before the world comes fully awake! There is no stillness like that of the dawn, nor anything like seeing the brightness of our home star clear the shadows and dreams of night and renew the colors of the day.

• Have you ever donated blood? This is one of the most noble and heroic acts a person can perform - willingly putting himself through pain to save the life of a complete stranger. When spilled senselessly, by violence, the red of blood symbolizes death; but when donated for the sake of good, it is a powerful symbol of life, of the altruism that one human can feel towards another. In view of the always-desperate need, all those who can donate blood should do so as often as possible.

• Have you ever considered the colors of the spectrum? I once had a thought: if an extraterrestrial who had never seen Earth before were to visit our home planet, perhaps the one thing that would strike him the most would be our planet's abundance of light. There must be places in the universe where light is a rare and precious treasure, yet we have it in limitless golden abundance. In even the most mundane scene, there are more colors than can be counted, more marvelously subtle shades of tone and hue than can be named. If we had eyes that saw only shades of grey, we would lose but little information about the world, yet how much more lacking in texture and life our perceptions would be!

• How often have you listened to music? Like storytelling, the making of music is one of those acts human beings can engage in to create beauty for themselves, and one that carries a profound message about us and the way we view the world. Music can expand our horizons and transport us to worlds beyond the realms of the mundane. With string and wind, brass and silver, we weave rhythms and harmonies that speak to that which is deepest in all of us, a language as nuanced as that created by the greatest masters of the written and spoken word. It was the music of our planet that was sent on the golden records carried by the Voyager spacecraft even now hurtling endlessly beyond our solar system, a message in a bottle cast adrift on the vast ocean of cosmic dark. Though they may never be found, nor understood if ever they are found, we will at least have used our chance to make a statement, in the most fundamental sense, about who we are and what we are capable of.

• How often have you looked up at the sky? The heavens have as many moods as human beings. One could do this every hour of every day of a full human lifetime and never see the same sky twice. There are days when the sky is heavy with pale white and sculpted gray, the shadows of clouds like sketches in charcoal, and there are days when the sky is clear, endless golden blue, bright with warmth and life. There are dawns in orange and silver and twilights ablaze in red and violet; evenings dark as midnight and indigo and ones where the entire vault of the heavens is like a bright sea breaking on distant shores. And then there are the clouds, which take such fantastic shapes: waterfalls, vast mountain ranges, wispy streaks and contrails, arcs and discs, rippling flags and curtains, broad bands, smoky slow-motion avalanches, enormous rolls like cotton bales, tremendous swelling anvils and plumes, aerial islands and continents. It is easy to see why people have always believed the sky was the home of the gods: it offers us a glimpse of something beautiful and celestial, infinitely above the concerns of the mundane earthly world.

• Have you ever considered the small acts of human kindness, those that happen around us every day? They may be as basic as holding a door for a stranger or helping someone across the street, as simple as the pleasures of love, family and friendship, or more profound, such as comforting a grieving friend or helping another through times of distress. Though human beings are capable of terrible acts of evil, by these good deeds we also show that within each of us is the potential for redemption and the hope of becoming better than we are. Compassion is our heritage, if only we learn to use it well.

• Have you ever watched a bird in flight? Do they feel joy, I wonder, soaring beyond the reach of gravity? Do they exult in the freedom of flight? Each kind brings its own character to the air: the swift blurred darting of a spray of sparrows, the plaintive cries of a circling gull, the ragged black wings of a crow flapping like a pair of hands applauding, the lofty glide of a hawk floating on air currents, its wings motionless, like a king not deigning to touch the earth. For ages we have dreamed of flying, and though today we ply the skies in great silver ships, still we cannot soar as they do. But though our bodies are earthbound, when we see a bird take wing, our minds can lift off the ground along with them.

• Have you ever watched a rainfall through glass? Have you ever listened to its music as it splashes to earth, observed its wet glistening on the green leaves of trees, the patterns of concentric circles rippling in puddles and streams, the scent in the air both sweet and earthy at the same time? There is beauty in even the gentlest rain: the earth drinks, and it brings life. But at the same time, there is power in the rain. Have you ever stood beneath a pouring shower or a raging thunderstorm? It is a spectacular sight to see bolts of lightning cleaving the dark sky, illuminating vast mountains and canyons in the clouds for a brilliant instant, followed by a crash of thunder that makes the earth tremble. And when the storm clears: bright rays streaming yellow through the breaking clouds, colorful reflections rippling in calm pools of water, sunlight scattering off droplets of mist in the air so that the whole world seems to glow with subtle light, and maybe, if you're lucky, the evanescent watercolor arc of a rainbow.

• Have you ever considered the trees? Though their kind of life is far grander, slower and more patient than ours, they are each individuals, as different as human beings are. They add beauty to the world, give peace in their dappled shade, freshen the air and enrich the earth, and turn even the most hard-edged urban environment into a blossoming garden. We humans grew up beneath the trees, and we love them still: mighty oaks, sweet red and silver maples, flowering dogwood, quaking aspen and yellow birch, fragile green willow, dark hoary evergreen, bright rainforest mahogany, palms of the tropical sea, and still more kinds than can here be named. And then there are the seasons! In sweet spring, when bright buds appear on every branch and the warm air and damp earth are permeated with the smell of growth, then it is easiest to believe that trees are living beings just like you or me. In summer, their leaves spread into a living cathedral that drinks the sun and filters the light into gold-speckled shade. And in autumn, leafy green gives way to an explosion of color: reds and browns and yellows and golds, a last fiery bloom in defiance of coming frost and slumber, whirlwinds of crackling sheaves stirred up by the breeze and crunching underfoot, the crisp dry-wheat smell of harvest in the air.

• Have you ever watched a snowfall? The winter has its own austere and solemn beauty, different from that of the growing seasons, but in its own way, no less beautiful. Winter touches every sense: the smell of ice crystals and woodsmoke in the air, the crisp bite of the whistling cold wind that brings showers of powder from evergreen tree branches and stings and numbs the hands, the crust of the snow cracking underfoot, the sticklike gray of leafless trees rising from white snow and clouded silver ice. Granted, this weather is inimical to us, but when one has a home to go back to, the chill of winter makes one appreciate the warmth and comfort of the hearth all the more. And nothing is more beautiful than being awake in the dark and secret hours of the early morning, watching the falling snow silently blanketing the slumbering world in peaceful, pristine white.

• Have you ever stargazed on a clear dark night, far from the lights of civilization? On such a night, with the stars like a scattering of diamond dust across the black vault of the heavens, it is easy to understand why the ancients thought the sky was a vast domed firmament arching over the world. But the truth is even more awe-inspiring: each of those faint twinkles is a great sun like our own, though unimaginably far away, and what you see are the lonely few photons that set out from their home star tens of thousands of years ago, that have traveled for trillions of miles across the gulfs of space to finally arrive at the small blue world that is our Earth, and at the terminus of this vast journey, passing through your pupil and striking the retina of your eye, becoming electrochemical flashes carried through the optic nerve and into your brain - becoming thought, a thought that began in the fiery fusion of hydrogen atoms in the heart of a star across the galaxy, or across the entire visible universe, before human civilization or even the human species existed.

While I have listed some of the things I take pleasure in, there is no universal key to happiness. Different things doubtless will work for different people. But those theists who believe happiness can only be found through belief in God are badly mistaken. They are looking hopefully to heaven and entirely failing to notice that there is a vast and beautiful world all around them. Why invent new sources for that which we already have in abundance? Reality is beautiful and meaningful all on its own.

In fact, paradoxical though it may seem, nature becomes more beautiful when we realize it is a thing in its own right, independent of us, and not just created for us to appreciate. This latter view reduces the fantastic intricacy of the natural world to something like a stage backdrop: scenery only, a shadow of the real thing, a mere theater on which the story of human salvation is played out. Does this not diminish the grandeur of nature? Is this view not egotistical in the extreme? Some may accuse me of worshipping the creation while denying the creator, but I will never understand the arrogance of one who cannot appreciate beauty without believing it was all made just for him.

Though we may appreciate the magnificence of the natural world, we must not lose sight of the fact that nature all too often acts in ways that, to us, seem capricious or senseless or cruel. Life is a painting done in shades both of dark and light. If we hold to the logical principle that a creation reflects the personality of its creator, then we must conclude that if nature is the product of an intelligent being, that being must be capable of great evil as well as great beauty. However, if we conclude that nature simply exists in itself, then it is no surprise that it contains examples both of breathtaking grandeur and senseless cruelty, for natural forces which do not take human needs into account may act either in our favor or against us, depending on chance. In either case, we, as human beings, must care for each other; but this does not preclude us appreciating the natural world for its often glorious and fantastic beauty. An atheist can have a life as full, rich and worthwhile, with as much opportunity for happiness, as any religious believer. When we can find beauty in the mundane, we need no gods to make our lives meaningful - merely to be alive is enough.