Cosmos - Carl Sagan [24]
Physics and chemistry permit such lifeforms. Art endows them with a certain charm. Nature, however, is not obliged to follow our speculations. But if there are billions of inhabited worlds in the Milky Way Galaxy, perhaps there will be a few populated by the sinkers, floaters and hunters which our imaginations, tempered by the laws of physics and chemistry, have generated.
Biology is more like history than it is like physics. You have to know the past to understand the present. And you have to know it in exquisite detail. There is as yet no predictive theory of biology, just as there is not yet a predictive theory of history. The reasons are the same: both subjects are still too complicated for us. But we can know ourselves better by understanding other cases. The study of a single instance of extraterrestrial life, no matter how humble, will deprovincialize biology. For the first time, the biologists will know what other kinds of life are possible. When we say the search for life elsewhere is important, we are not guaranteeing that it will be easy to find—only that it is very much worth seeking.
We have heard so far the voice of life on one small world only. But we have at last begun to listen for other voices in the cosmic fugue.
*Although traditional Western religious opinion stoutly maintained the contrary, as for example, the 1770 opinion of John Wesley: “Death is never permitted to destroy [even] the most inconsiderable species.”
*In the Mayan holy book the Popol Vuh, the various forms of life are described as unsuccessful attempts by gods with a predilection for experiment to make people. Early tries were far off the mark, creating the lower animals; the penultimate attempt, a near miss, made the monkeys. In Chinese myth, human beings arose from the body lice of a god named P’an Ku. In the eighteenth century, de Buffon proposed that the Earth was much older than Scripture suggested, that the forms of life somehow changed slowly over the millennia, but that the apes were the forlorn descendants of people. While these notions do not precisely reflect the evolutionary process described by Darwin and Wallace, they are anticipations of it—as are the views of Democritus, Empedocles and other early Ionian scientists who are discussed in Chapter 7.
*The genetic code turns out to be not quite identical in all parts of all organisms on the Earth. At least a few cases are known where the transcription from DNA information into protein information in a mitochondrion employs a different code book from that used by the genes in the nucleus of the very same cell. This points to a long evolutionary separation of the genetic codes of mitochondria and nuclei, and is consistent with the idea that mitochondria were once free-living organisms incorporated into the cell in a symbiotic relationship billions of years ago. The development and emerging sophistication of that symbiosis is, incidentally, one answer to the question of what evolution was doing between the origin of the cell and the proliferation of many-celled organisms in the Cambrian explosion.
CHAPTER III
THE HARMONY OF WORLDS
We do not ask for what useful purpose the birds do sing, for song is their pleasure since they were created for singing. Similarly, we ought not to ask why the human mind troubles to fathom the secrets of the heavens.… The diversity of the phenomena of Nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment.
—Johannes Kepler, Mysterium Cosmographicum
If we lived on a planet where nothing