The habitability of our planet—is it only a contemporary issue?

Over the past decade various states and scientific agencies that promote science at a global level and study climate change have invested in research programs to study the habitability of our planet and also of other planets. They have sought to understand some forms of adaptation and resistance that certain organisms have in extreme ecosystems (poles, deserts, etc.), and to find elements that would allow life to be facilitated in other places. For example, some NASA projects seek to understand the impact of atmospheric modifications on the planet, but also to go beyond the frontiers of our own world. The search for new habitable planets, or exoplanets, is an example of this. The main motivation is to advance knowledge, but there are those who think that this is also preparation for an eventual catastrophe that will make the earth uninhabitable (think of the movie Interstellar).

In all these investigations, in which scientists from various disciplines (astronomers, physicists, marine biologists, etc.) participate, habitability is understood as the capacity of a region to support the life of humans or of other organisms for a significant period of time (without entering into crisis by major climatic transformations). One of the most important requisites is fresh water. Of course, many large-scale factors influence or determine the habitability of a planet, such as the force of gravity, the nature of the star it orbits, etc.

But questions about habitability are not new. Habitability is a notion that has been present throughout the centuries, and that has its own history. Studying that history can shed light on our own interactions with it and can be vital to understanding the different ways of perceiving life, its limits, the imaginaries that shape the search for knowledge, and our visions of the future.

The concept of habitability was created in antiquity and developed during the Middle Ages. It was a topic of discussion among the main cosmographers and geographers who reflected on the nature of our planet: Parmenides, Aristotle, Strabo, Ptolemy, Macrobius, and St. Augustine, among others. However, until the end of the fifteenth century the concept of habitability was different from the one we have today. It was associated with a climatic theory that divided the world into five zones, two of them habitable and three uninhabitable.

In the polar regions as well as in the equatorial zone, human life was thought to be impossible; in the equatorial zone because of the heat (the Torrid Zone), and near the poles because of the cold and the long nights. The habitable zones were the temperate zones in the middle latitudes between the hot and the cold, one in the northern hemisphere and another in the south. The northern zone corresponded to the “known” world of Europe, Asia, and Africa, while the southern one, if there was land there (which was uncertain), was thought to be inhabited by monsters.

Two events at the beginning of the modern era made it possible to reconfigure this long-lived notion: the appearance on the European radar of the Americas in 1492 and the European discovery of the Strait of Magellan in 1520, which led to European circumnavigation of the planet, completed in September of 1522. This latter milestone was decisive: thanks to it, all the oceans of the world were understood to be connected for the first time, empirically demonstrating the sphericity of the earth and also the possibility of inhabiting all its parts. This voyage destroyed the “theory of zones” because it verified that from the torrid zone almost to the South Pole there were conditions for the development of life and non-monstrous peoples. It also disproved the Aristotelian idea that the world was one great landmass surrounded by water.

At the same time, it brought to light almost a third of the previously unknown (to Europe) world (from the 35th degree south latitude to the 53rd). These changes had an impact on European ideas about the measurements and limits of the earth, in what were thought to be its heights, latitudes and longitudes, which led cosmographers and geographers to rethink their postulates, and to criticize the inaccurate conceptions and calculations made by the ancients. Throughout the sixteenth century, we see how authorities and scholars of the European courts, specialists in theology, cosmography, geography, and natural philosophy, debated and considered new evidence on the subject. The resulting changes were portrayed in numerous maps, cosmographies, and natural histories. This rethinking and production of new knowledge took place within a mantle of geopolitical interests that cannot be ignored, which sought to use this knowledge to further the commercial and colonial enterprises that were beginning to multiply.

One of these works, which is in the Folger Shakespeare Library, has allowed me to study this change in the perception of habitability and its consequences during this century in Europe. I refer to the work of the English physician, astrologer and engraver William Cuningham. His book The cosmographical glasse: conteinyng the pleasant principles of cosmographie, geographie, hydrographie, or nauigation is one of the few English works that attempts to explain the spatial paradigm shift that occurred at the time.

The work was published in 1559 and is divided into five books or sections; according to the author, it seeks to establish the importance of the sciences in understanding the planet, above other arts and “ignorances” that abounded at the time. Cuningham is interested in the new processes of measurement and description of the Earth and, to this end, he supplies a series of images and tables that allow the reader to obtain a general idea of ​​the work of cosmography. In fact, he is aware that this material added considerable value to his book: “What diligece I haue giuen in time of the Printing, to the correction hereof, and also in divisinge sundry newe Tables, Pictures, demonstrations, & praeceptes: that you may easely judge by readying the same work” (The Preface).

He is aware that he is the first writer in English to address his subject, and of the risks that this entails: “And if for the difficulty of the worke, any error escape: remember I am the firste that ever in our tongue have written of this argument, & therfore am constrained, to finde out the pathe” (Preface)

His main task is to distinguish among the sciences that study the new lands discovered in voyages of exploration. Thus, he pays special attention to explaining the difference between cosmography and geography as sciences that explain the world. His book has the form of a “Renaissance colloquy,” that is, an educational dialogue between two characters, Spodeus and Philonicus.¹ For example, Philonicus thus explains to Spodeus the difference between cosmography and geography:

You have truly repeated Ptolomaeus words. Now I will prove by your definition, that you have erred two ways, in putting no difference between Cosmographie, and Geographie. First Cosmographie teacheth the description of the universal world, and not of the earth only: and Geographie of the earth, and of none other part.

This journey of questions and answers between the two interlocutors allows us to appreciate the central topics in this change in ideas about habitability: the distinction between terrestrial and aquatic spaces; the relevance of the sky, its stars and the zodiac; the influence of the sun and shadows in the new calculations and terrestrial characterizations; as well as the importance of the horizon line and declination in understanding and measuring the globe.

Climates, lunar cycles and phenomena such as eclipses are also discussed in the text. In all of these subjects there is a cloak of poetry and fiction, which is characteristic of this time period. The assertions were not entirely proven, so part of what was taught was hypothesis or imagination, a tool with which Europe began to colonize the world.²

Cuningham also reflects on what I understand to be another aspect of habitability, namely the dimensions of the human. This comes out in some of his ideas about the origins of peoples, the notion of race, and the effect of the sun on skin color in different regions. Thus Cuningham includes something that appears in other cosmographies as well: reflections on how the different “types” of humans are defined according to their location in the world, which I believe influenced European colonial enterprises, particularly with regard to the importance of the difference between the north and the south.

William Cuningham’s work is little known in comparison with other cosmographic works of the same decade that had a greater impact in Europe, such as that of Sebastian Münster, or the maps produced by Guillaume le Testu and the Spanish Casa de Contratación through its Venetian and Genoese cartographers. But thanks to this work, today we can know part of what was discussed in England under Elizabeth I, and we can compare it with other works that offer historical reflections on the expansion of the oikoumene in the same century. It is important to know how the idea of habitability was configured or had different faces in different places, as happened in each European court. Each kingdom represented the world in its own way, according to its own interests, and that influenced its views of particular territories and their inhabitants; at the same time, it promoted new knowledge that was key to the development of new sciences.

It is also vital to compare these cosmographies and the way in which geographical information was categorized in the sixteenth century with these practices in other periods. In this way, it will be possible to observe in a historical perspective how philosophers and scientists have thought about habitability and indeed about the future of humanity. This type of reflection can generate new interdisciplinary alliances, since habitability is not only a question of resistance or adaptation of flora and fauna, but also of imaginaries, expectations and political decisions related to humanity, where history can contribute elements for its understanding.