In all ages, we are constrained by that which we think we know because it determines what we think we see

From American Heroes by Edmund S. Morgan, page 3.

We generally are aware of confirmation bias but take it little into account when considering people of the past as they encountered new things which they attempted to force fit into their already existing world view.

In the year 1513 a group of men led by Vasco Núñez de Balboa marched across the Isthmus of Panama and discovered the Pacific Ocean. They had been looking for it—they knew it existed—and, familiar as they were with oceans, they had no difficulty in recognizing it when they saw it. On their way, however, they saw a good many things they had not been looking for and were not familiar with. When they returned to Spain to tell what they had seen, it was not a simple matter to find words for everything.

For example, they had killed a large and ferocious wild animal. They called it a tiger, although there were no tigers in Spain and none of the men had ever seen one before. Listening to their story was Peter Martyr, member of the King's Council for the Indies and possessor of an insatiable curiosity about the new land that Spain was uncovering in the west. How, the learned man asked them, did they know that the ferocious animal was a tiger? They answered "that they knewe it by the spottes, fiercenesse, agilitie, and such other markes and tokens whereby auncient writers have described the Tyger." It was a good answer. Men, confronted with things they do not recognize, turn to the writings of those who have had a wider experience. And in 1513 it was still assumed that the ancient writers had had a wider experience than those who came after them.

Columbus himself had made the assumption. His discoveries posed for him, as for others, a problem of identification. It seemed to be a question not so much of giving names to new lands as of finding the proper old names, and the same was true of the things that the new lands contained. Cruising through the Caribbean, enchanted by the beauty and variety of what he saw, Columbus assumed that the strange plants and trees were strange only because he was insufficiently versed in the writings of men who did know them. "I am the saddest man in the world," he wrote, "because I do not recognize them."

By 1524, when Gonzalo Fernández de Oviedo, a Spanish royal official, sat down to write about the wonders of the new land, explorers were assuming a more skeptical attitude toward the knowledge that could be gained from the ancients. Oviedo had just returned to Spain from several years in Darien, on the isthmus earlier crossed by Balboa. He, too, had encountered the alleged tiger, but he was not so sure that it was in fact a tiger. "I will not obstinately stand in opinyon," he said, "whether these beastes bee tygers or Panthers, or of the number of any other such beastes of spotted heare." It was quite possible, he thought, that this was "sum other newe beaste unknowen to the owlde wryters," for by 1524 it had become clear that "thys greate parte of the worlde was unknowen to the antiquitie."

As the century wore on and the caravels of Spain probed the dimensions of the new land, it gradually expanded into a New World, and the challenge to traditional ideas expanded with it. The Jesuit missionary Jose de Acosta, sailing to Peru in 1570, still thought it proper to prepare him-self by reading what the old writers had said of lands in that latitude, and having read he feared the worst. The heat, they said, would be too great for human life, the sun too hot to bear. But arriving in Peru in what was summer there, the month of March, he found the weather so cold that he welcomed the chance to bask in the sun. "What could I else do then," he asked, "but laugh at Aristotle's . . . Philosophie, seeing that in that place and at that season, whenas all should be scorched with heat, accordinge to his rules, I, and all my companions were a colde?"

America released Father Acosta from Aristotle's error, and it almost released him from the Bible, too. A better botanist than Columbus, he recognized that many of the plants and animals of the New World were unique, unlike anything known to the ancients from their experience of Europe, Asia, and Africa. And he asked himself how this could be. How did they get to America and not to Europe? It occurred to him that they might have come into existence there. But if this was the case, he realized, it made the whole story of Noah's ark a little shaky; "neither was it then necessary to save all sorts of birds and beasts, if others were to be created anew. More-over, wee could not affirme that the creation of the world was made and finished in sixe days, if there were yet other kinds to make, and specially perfit beasts, and no lesse excellent than those that are knowen unto us."

Father Acosta, discerning a few of the consequences of his daring thought, drew back from it, as did everyone else. He concluded at length that the universal deluge had been followed by an immediate dispersal from the ark and that some animals went in one direction and some in another. Thus he preserved Noah and the deluge and left the Bible unassailed as a source of historical knowledge.

We need not deride Father Acosta's reluctance to give up the world that he knew from books. Only idiots escape entirely from the world that the past bequeaths. The discovery of America opened a new world, full of new things and new possibilities for those with eyes to see them. And Father Acosta saw many of them. But the New World did not erase the Old. Rather, the Old World for several centuries determined what men saw in the New and what they did with it. What America became after 1492 depended both on what men found there and on what they expected to find, both on what America actually was and on what old writers and old experience led men to think it was or ought to be or could be made to be.