SINCE COPERNICUS DISCOVERED, IN THE sixteenth century, that the earth travels around the sun instead of vice versa, science and religion have often found themselves on a collision course. Religion depends upon faith—a belief in something that cannot be proved. Science, on the other hand, depends upon proof. But as two San Antonio men discovered this year when they set out to “prove” whether a highly revered image of the Virgin Mary in Mexico City, known as Our Lady of Guadalupe, was painted by miracle or by man, facts are subject to interpretation, especially when religion is involved. In a year of controversy for the Catholic Church, the authenticity of the image is as highly charged as the issue of pedophilia. Our Lady of Guadalupe is not just a religious symbol; she serves as a political symbol of female power and, because her appearance and garments are unmistakably of the New World, as a cultural symbol uniting Latino Catholics throughout the Western hemisphere. Pilgrims flock by the thousands each day to the Basilica de Nuestra Señora de Guadalupe in Mexico City to view the painting.

The scientific quest started in February 1999, when Leoncio A. Garza-Valdes, a San Antonio pediatrician, microbiologist, and amateur archaeologist, decided to tackle the question of the image’s authenticity. Catholic tradition holds that in December 1531, one year after Copernicus first announced his findings about the relationship between the planets and the sun, the Virgin Mary appeared to Juan Diego Cuauhtlatoatzin, an Indian peasant. In the vision, the Virgin had dark skin and Indian features. She spoke to Diego in Nahuatl, the language of the Aztecs, and told him that she wanted a temple built on the hill known as Tepeyac. To convince the bishop of Mexico City of the authenticity of the vision, the Virgin provided Diego with tangible proof; she gave him roses, wrapped in his blanket, or tilma, which was made of agave fiber. When Diego opened the tilma to present the roses to the bishop, the image of Our Lady was painted on the cloth. The question that concerned Garza-Valdes is one that has preoccupied the Catholic Church for almost five hundred years: Is the image on Juan Diego’s blanket of earthly origin?

It’s impossible to understand the depth of emotion implicit in this question unless you understand how central Our Lady of Guadalupe is to Catholicism in most of the Western Hemisphere. Our Lady of Guadalupe appeared only ten years after the conquest of Mexico by the Spanish. The image served as a bridge between the two cultures and was a major factor in the Christianization of the Indians. In 1810 Father Miguel Hidalgo carried a banner with an image of Our Lady while declaring Mexico’s independence from Spain; more recently, Cesar Chavez’s farm workers carried one as well. Today she remains a broad and elastic symbol capable of encompassing many points of view, some of them contradictory. Her image appears everywhere—in churches, in the yards of rich and poor, on the hoods of lowrider cars, and on the “In Guad We Trust” bumper stickers on Suburbans, including my own. To believers, Our Lady is a revered, intimate mother—a nice balance to the dominant image of God the Father. To feminists such as San Antonio novelist Sandra Cisneros, she is a symbol of flesh-and-blood female empowerment. In a book of essays titled Goddess of the Americas, Cisneros wrote that as a child, she found Our Lady of Guadalupe too remote an ideal—”a goody-two-shoes”—but as a woman, she now regards her as a source of sexual and female power.

Such imaginative ideas are inimical to scientists, even scientists who are believers. Garza-Valdes’ interest in the tilma was a matter of both faith and science. When he was a child growing up in Monterrey, Mexico, Our Lady was as real to him as his own mother. “I was sucking at my mother’s breast when I first heard the story of how she appeared to Juan Diego and united all of Mexico,” says Garza-Valdes, a robust, bald man of 61 with the classic profile of a Spaniard and the dark, smiling eyes that go with it. He went to Catholic schools, joined the Society of Mary when he was in high school, and even now, after more than thirty years in private practice as a pediatrician and thousands of hours in microbiology labs, Garza-Valdes is a believer—in God and in Our Lady of Guadalupe.

But because of his scientific inquiry into the image of Our Lady, Garza-Valdes no longer believes that she appeared to Diego. He thinks Pope John Paul II made a “big boo-boo” when he canonized Diego in July in Mexico City. “I don’t believe that Juan Diego ever existed,” he says. “Next time, the pope might canonize some other nonexistent person.”

As an archaeologist, Garza-Valdes has studied ancient artifacts, particularly artifacts of the Mayan culture, for many years. “In my younger days I thought of myself as something of an Indiana Jones,” he says. In 1999 he made international news when he published the results of his discovery of an organic “bioplastic coating,” a bacterial excretion that affects carbon 14 dating, on the Shroud of Turin, believed to be the burial cloth of Jesus. In a book called The DNA of God?, published by Doubleday, Garza-Valdes concluded that the shroud, which is on display in St. John the Baptist Cathedral in Turin, Italy, is from the first century and is therefore possibly a relic of the time of Jesus of Nazareth. The book was hailed by many Catholics, and Garza-Valdes presented a copy of it to Pope John Paul II. As a result, church officials at the basilica in Mexico City asked Garza-Valdes to do similar research on the famed image.

Garza-Valdes invited 56-year-old Gilberto Aguirre, a fellow physician, friend, and neighbor in San Antonio with a long interest in Our Lady, to go with him to Mexico City. The two men hired Lester Rosebrock, a medical and scientific photographer from the University of Texas Health Science Center in San Antonio, to take ultraviolet and infrared photographs of the Virgin of Guadalupe image.

Once in Mexico City, the trio had to make arrangements to gain access to the image. As usual, the basilica was mobbed with tourists and pilgrims, many of whom stood on a moving sidewalk inside the church to get a glance at the image. The three men were allowed to see the image one night around ten o’clock, after the basilica was closed. They were ushered into the small vault where the image is kept after-hours. The space had only two lights, and the priests would not allow Rosebrock to set up additional ones. Nor would they allow him to remove the quarter-inch-thick sheet of Plexiglas that covered the image. Nonetheless, Rosebrock took about fifty shots, using both ultraviolet and infrared light.

Five days after the trio’s return to San Antonio, Rosebrock finished developing the film, and it was then that Garza-Valdes saw one thing and Aguirre saw another. “What I saw was not one image, but three different paintings—one on top of the other,” says Garza-Valdes. “The first image shows a small baby in the Virgin’s left arm. I believe this image was painted in 1556 by Marcos Aquino in Mexico. In other words, more than twenty years after Juan Diego supposedly saw his vision. The second and third paintings show changes in the Virgin’s face; in the final image, her eyes are half-closed, her skin is lighter, and her features are less Indian.” His conclusion? “This is a man-made painting, completely overpainted twice,” says Garza-Valdes.

Aguirre disagrees. He says the photos taken in Mexico do reveal changes in the image—particularly changes in the Virgin’s facial features—but he says they don’t show any underpaintings at all and maintains that the photos can’t be relied upon because the Plexiglas blocked some of the light and created reflections. Besides, he says, ultraviolet photographs detect only the surface of paintings, not the subsurface painting. Scientists, as it turns out, have to have faith too—in their experiments. Aguirre has none. “This is a totally flawed scientific study,” he says. “It proves nothing.”

Aguirre believes that the image could be miraculous. He has two black and white photographs of the image, one taken in 1923 and the other in 1930, that reveal man-made changes. During that time, when the church in Mexico experienced persecution, the image of Our Lady was taken by priests to a family home in Mexico City. It was there that the changes were made, but according to Aguirre, that does not mean that the original image could not be supernatural.

There is a second crucial piece of scientific evidence about which the two men disagree. The priests at the basilica supplied them with a piece of thread from the cloth in Mexico City. Based on studies in his laboratory, Garza-Valdes says the specimen supplied to him was made of hemp, not of agave fiber, as Juan Diego’s tilma was purported to be: “If it’s not agave, then it was not the tilma and therefore the whole Juan Diego story falls apart. Hemp was used by artists for canvases after 1550.”

Again, Aguirre has a different interpretation of the facts. He says the specimen given to the two men may have been taken from the edge of the tilma, not the center, where the Virgin’s image appears. According to Aguirre, it was common until the nineteenth century for churches to line the edges and undersides of precious images with hemp or linen. “The original image could be on cactus and this could be the lining,” says Aguirre. “Again, our study is flawed. In my opinion, the ultraviolet image of Our Lady of Guadalupe could almost be considered a Rorschach test for Dr. Garza-Valdes. Perhaps he is seeing in her what he wants to see. To me, the material image is immaterial. I look at her and see only hope.”

Garza-Valdes will publish his findings in a forthcoming book titled Tepeyac: Five Centuries of Deceit, scheduled for release this month in Mexico City by Random House. “For me, there is no conflict. I am a scientist and a man of faith,” he says. “I believe in Our Lady of Guadalupe. I just don’t believe she appeared to a man called Juan Diego.”