On the cover of Being Human , the anthology of writings collected by the President’s Council on Bioethics under Leon Kass’s stewardship, there is a picture of a ballerina leaping into the air, body extended, gazing and reaching and soaring toward the heavens, looking at once perfectly natural and unnaturally perfect. Of all possible snapshots, Kass deliberately chose the ballerina to represent the living human”an image that celebrates our embodiment and not our rationality alone, our yearning for the beautiful and not our ordinariness alone. The ballerina is the graceful human animal at her best”one of us, to be sure, yet also separated from us by the heights to which she can reach, by the elevated posture she assumes, and by the pleasure that she brings to those who behold her. And while we fellow humans may watch her in awe, her perfection-seeking performance seems more like an offering to the divine, which her body seeks at the very peak of her movement.

Now consider the very different posture of the worshipper bowed down in prayer, prostrate rather than soaring. In those rarest moments in Jewish liturgy, coming once on Rosh Hashanah and again on Yom Kippur, the worshipping Jew lies face to the floor, hands over his eyes, in a bodily act of fear and reverence. Unlike the ballerina, the bowed worshipper’s body is abject, frozen, limp, needy. Such prostrations, called for only on the holiest days of the Jewish year, are not the achievement of the graceful few but the practice of the God-fearing many. In fulfilling this ritual obligation, the mass of worshippers imitates the awe-filled body of Moses, who hid his face in fear on hearing the voice behind the burning bush, and later fell to the ground after destroying the tablets of the law that his stiff-necked people were unworthy to receive.

Head up or face down, the soaring ballerina or the bent man of prayer, the human animal shows his distinctness from the other animals through the forms and activities of his body. The monkey, for all his leaping, produces no ballerinas; the snake, cursed forever to the ground, never lies face down in reverence. Kass”who delivered the 2009 Jefferson Lecture, the nation’s highest honor in the humanities”is first and foremost a philosopher of the body. For decades, he has reflected on the mystery of Moses and the ballerina: two peaks, each divine-seeking, taking the body in opposite directions. His subject is man, the God-seeking animal.

I once asked Kass which piece of his own writing gave him the greatest pleasure and pride. He paused, smiled, and directed me to a passage about a squirrel:

What, for example, is a healthy squirrel? Not a picture of a squirrel, not really or fully the sleeping squirrel, not even the aggregate of his normal blood pressure, serum calcium, total body zinc, normal digestion, fertility, and the like. Rather, the healthy squirrel is a bushy-tailed fellow who looks and acts like a squirrel; who leaps through the trees with great daring; who gathers, buries, covers but later uncovers and recovers his acorns; who perches out on a limb cracking his nuts, sniffing the air for smells of danger, alert, cautious, with his tail beating rhythmically; who chatters and plays and courts and mates, and rears his young in large, improbable-looking homes at the tops of trees; who fights with vigor and forages with cunning; who shows spiritedness, even anger, and more prudence than many human beings.

It is a beautiful passage, even for those whose sensibilities (like mine) are not naturally attuned to the wonders of nature and to the aliveness of our fellow animals. (My young children, I have learned, are quite attuned, especially to squirrels.) We, too, are animals with bodies and doings”conceived and then born, nursing and then eating, crawling and then walking, babbling and then speaking, getting sick and then getting well, growing up and then giving birth, working and then resting, aging and then dying. Yet we are also animals with a difference”animals who think and sin, sanctify and degrade, live in darkness and yearn for God.

In Kass’s great work The Hungry Soul , he explores one of those activities”eating”that we share with the other animals. Like them, we need to eat to live. Like theirs, our infants know instinctively where”from whom”to find nourishment. Like them, we cannot take for granted the food we need in order to live; we rely on nature’s bounty for our sustenance, and our young rely on their elders to feed them. Yet man alone incorporates food into an elevated way of life. Man alone dines with old friends in fine restaurants, says grace before meals, and separates milk and meat in observance of the laws of kashrut. Man alone constrains his appetites in the name of civility or holiness. We are, in other words, not only hungry bodies but hungry bodies with hungry souls”souls that yearn for the community of friends and for the sanctification of animal life, souls that adorn animal necessity with beauty and refinement and that elevate metabolic necessity in obedience to the transcendent.

Eating is just one example of man remaining an animal while seeking to be more than an animal. Like other animals, we are born into the world, but man alone performs the bris and the baptism, bodily acts that symbolize the newborn’s new relationship with the covenant-making and history-redeeming God. Like other animals, we die; but man alone buries the dead with rituals of remembrance, thinking beyond the lifeless body to the possibility of immortality. In one realm in particular”as sexual animals”we demonstrate both our animal nature and our potential transcendence of it.

Sexual desire, like all forms of desire, is always and only felt by an individual animal: the lone wolf, the lone ape, the lone man. The individual body is aroused, and the lusting animal covets both intensification and relief of that arousal. The sexual impulse drives the aroused animal toward the body of another who is like yet unlike, the complementary counterpart. This is equally true of monkeys and of men. But then comes the crucial turn, when the animal becomes the human animal. As Kass describes it, following Genesis:

Man became man when he became self-conscious not of his mortality but of his sexuality, of the uncanny and mysterious doubleness in his (animal) soul. He became human”rather they became human, man and woman together”when each saw through the eyes of the other the fact (and meaning) of their nakedness . . . . In turn, clothing and adornment, by means of refusal and its effects on the imagination, transform animal lust into human eros, which takes wings from the recognition that there are higher possibilities for man than the finally unfulfilling acts of bodily fusion. Among these possibilities are the establishments of long-lived familial societies, grounded in the awareness that sex means children, that human children need long-term rearing including rearing for sociality, morality, and love, and that children are indeed life’s (partial) answer to mortality.

Of course, Kass is here telling only the elevating part of the human story. Man’s sexual difference from the other animals also leads to his own unique capacity for self-degradation, and to his own unique power to turn against the natural transcendence of self that comes with procreation. Human beings alone are capable of adultery and prostitution as well as marriage. Human beings alone produce the culture of Britney Spears and Internet pornography as well as that of Jane Austen and the Song of Songs. And human beings alone can pursue animal-like sexual pleasure without animal-like procreative consequences. The ideology of the pill”not any pill, but the pill”rejects the intimation of permanence embodied in the marital vow and the intimation of immortality that comes with procreation. Man sometimes chooses, instead, the sterile pursuit of limitless physical bliss, which typically ends in the sadness of being buried without children to mourn, or remember, or carry on.

Kass, and the Hebrew Bible from which he learns, offers a different teaching about the layers of human sexuality and the sexual ascent of man. The first layer is lust, which leads us beyond ourselves: man to woman, woman to man. For the other animals, lust is the biological driver of a natural story in which each animal plays its part”and can play no other. For men and women, lust spurs a deeper psychological and, ultimately, moral-theological drama: The mere animal desire for union exists alongside an awareness of our nakedness, our neediness, our incompleteness. With this awareness, two roads diverge. The pagan path”which seeks the shame-free sexual satisfactions of the other animals without the animal (procreative) consequences of sex, and which seeks erotic union with one’s beloved without the burdens of progeny”is captured by the Roman poet writing to his mistress, “Let me be your one joy; you at my side, I have no need of sons to feed my pride.” The path of Jerusalem”sexual modesty before the other and before God, and lust governed by the unbreakable promise of marital fidelity and the God-seeking yearning for descendents”is captured in the story of Hannah and her son: “She named him Samuel, saying, ‘because I asked the Lord for him.’”

From lust to nakedness, from nakedness to shame, from shame to modesty, from modesty to marriage, from marriage to children, from children to the drama of accepting one’s own finitude and yearning for the transcendence of the biological self”this is God-seeking sex, the ascent of the body beyond the body. In the marital vow, husband and wife experience the intimation of permanence, of standing with this particular other forever and always. In the birth and rearing of children, father and mother experience the intimation of immortality, of life beyond themselves connected to them for eternity; and they experience the intimation of divine creation, of the godlike power of bringing new life into being out of themselves. But these intimations of the divine do not ultimately quench man’s yearning for what the Song of Songs calls the perfect seal upon thy heart, fiercer than death. Man and woman seek, also, to be known fully by the divine”a yearning that they express, at the peak of this erotic longing, in the ecstatic language of the body. To quote the opening lines of the greatest love poem ever written:

Oh, give me of the kisses of your mouth,
For your love is more delightful than wine.
Your ointments yield a sweet fragrance,
Your name is like finest oil”
Therefore do maidens love you.
Draw me after you, let us run!
The king has brought me to his chambers.
Let us delight and rejoice in your love,
Savoring it more than wine.

Man seeks this perfect love, but does he find it? “O you who linger in the garden, / A lover is listening; / Let me hear your voice. / Hurry, my beloved, Swift as a gazelle or a young stag, / To the hills of spices!”

This image of the gazelle is itself suggestive. In human sexuality, bodily vigor and bodily submission”our powers and our neediness”are both on display. We are invigorated, yet we are lying down. “Swift as a gazelle” suggests a different image of bodily vigor: the runner in stride or the ballerina at her heights. And here again, Kass observes, we are animals with a difference. Our running is both less easily natural and more possibly divine than the doings of the gazelles:

When we see an outstanding athlete in action, we do not see”as we do in horse racing”a rational agent riding or whipping a separate animal body . . . . So attuned is the body, and so harmonious is it with the heart and mind, that”in the best instance”the whole activity of the athlete appears effortlessly to flow from a unified and undivided being. At such moments the athlete experiences and displays something like the unity of doer and deed one observes in other animals, but with this difference: For humans, such a unity is an achievement. A great sprinter may run like a gazelle and a great boxer may fight like a tiger, but one would never mistake their harmony of body and soul for the brute instinct that spurs an animal toward flight or fight.

The gazelle surely runs with more grace, and arguably with more beauty, than most men. It is faster and more natural, surely a source of pleasure to its creator. But man alone, at his peak, performs in the knowing pursuit of perfection. Such a pursuit is dangerous indeed, and Kass has given strong moral voice to its potential dark side. In a stirring lecture at the United States Holocaust Memorial Museum, he warned against the pagan worship of the “glass man,” the idol of Weimar eugenics, a field that envisioned a master race of bodies engineered to perfection by the new science of genetics. Kass’s lecture reminds us of the ultimate worth of mere men, not glass men”the worth of men with imperfect, needy bodies, born messily of embodied mothers rather than conjured neatly in the laboratory. But this same critic of the glass man can himself take great pleasure in the striding Olympian and choose the soaring ballerina to represent us on the cover of Being Human . Kass thereby invites us to ponder the difference between worshipping the human body as an idol and appreciating the human being at work as an act of gratitude for the created gifts that man alone possesses: to soar like a ballerina, to run like an Olympian. And so Kass ends “For the Love of the Game,” his essay on sport, with a quotation from Eric Liddell, the Scottish runner, as captured in the remarkable film Chariots of Fire . Liddell explains why he cannot give up running”not just yet”to work as a Christian missionary in China: “I believe that God made me for a purpose, but He also made me fast, and when I run I feel His pleasure . . . . To give up running would be to hold Him in contempt.” His running, in other words, was itself an act of worship.

But the bodies of runners and ballerinas eventually will decline; the voices of our greatest singers will grow weak and off-pitch; the fingers of violinists will lose their strength and precision. The men and women who, at their peak, glimpse perfection with acts of the body will one day become like the rest of us”mere imperfect mortals, submitting to man’s limits, including the final limit that is death, and hoping their individual lives have some ultimate meaning. Even the most upright human animals cannot worship in the upright posture alone. And so they also bow their heads, and cover their faces, and cry out to the divine source of their own being in the hope that he exists, and that he cares.

There is a discussion in the Talmud about whether, on the high holidays of Rosh Hashanah and Yom Kippur, the worshipping Jew should blow a ram’s horn that is straight or a ram’s horn that is bent.

On what points do [the sages] argue? One master holds that on Rosh Hashanah the more a person bows his mind, the better it is; therefore, a bent shofar is used to reflect this attitude of submission and humility. And on Yom Kippur of the Jubilee Year the more a person straightens his mind, the better it is; therefore, a straight shofar is used to reflect this attitude of freedom. But the other master maintains that on Rosh Hashanah the more a person straightens his mind, the better it is; therefore, a straight shofar is preferable. And on fast days [such as Yom Kippur], the more a person bows his mind, the better it is; therefore, a bent shofar is preferred.

Where these two rabbis seem to agree, however, is that man is the being who alone approaches the divine both bent and straight, assuming each God-seeking posture in its proper season.

As one of the great philosophical anthropologists of our age, Leon Kass has tried to understand man as the upright being who bows his head in reverence. He has illuminated, in his writings and in his teaching, these two unique dimensions of our humanity: straight and bent, upright and bowing. As he wrote in his first book, the neo-Aristotelian Toward a More Natural Science , “We stand most upright when we gladly bow our heads.” And as he writes in his most recent book, the biblical The Beginning of Wisdom , “The upright animal, his gaze uplifted and his heart filled with wonder and awe, begins to suspect that he may in fact stand tallest when he freely bows his head.” In a body of writings that spans four decades and probes virtually every human subject under the sun”love, death, science, nature, men, women, progress, and eternity”this image of man, upright and head bowed, is the divine-seeking thread that ties it all together.

Eric Cohen is editor at large of the New Atlantis and publisher of the Jewish Review of Books . A longer version of this essay will appear later this year in Apples of Gold in Pictures of Silver: Honoring the Work of Leon R. Kass (Lexington Books)