Theme and Variation
Life not only appeared on Earth, it evolved into many millions of different species, one of which can even ask questions about itself and the universe. How did it work, this long unfolding and synthesis from microlbe to microbiologist? What pivotal influences guided evolution here? Would those same influences shape the nature and appearance of life elsewhere?
The physicist Guiseppe Cocconi, an early pioneer of SETI, remarked, "This probing of evolution is really a fantastic thing because we know only of one way evolution worked, on Earth. It is one history, our history. But there are probably millions of other roads ..." The problem of sample size— the lack of a second known living planet—is the bane of contemporary astrobiologists. But whereas life on Earth represents a single entry in an otherwise empty logbook, evolution offers us many different creatures to study. All may be of common stock, yet they give us a healthy basis for seeing how the forces of evolution play out over long periods and in different ecological settings. The dazzling yet bounded variety around us contains clues to the kind of life we can expect on other worlds.
Evolutionary theory has itself evolved and continues to do so, as competing ideas battle for scientific supremacy. Its modern story begins in late eighteenth century France with Jean-Baptiste Lamarck, keeper of the royal garden and later professor of invertebrate zoology at the Museum of Natural History in Paris. In his Philosophie zoologique, published in 1809, Lamarck put forward the first theory in which organisms were seen to change and evolve by a gradual process of adaptation to their environment. According to his scheme of "inheritance of acquired characteristics," small physical changes