CASE 1 The First Cell: Life’s Origins

In Chapter 1, we considered the similarities and differences between living and nonliving things. Four billion years ago, however, the differences may not have been so pronounced. Scientists believe that life originated early in our planet’s history, formed by a set of chemical processes that, through time, produced organisms that could be distinguished from their nonliving surroundings. How can we think scientifically about one of biology’s deepest and most difficult problems? One idea is to approach life’s origins experimentally, asking whether chemical reactions likely to have taken place on the early Earth can generate the molecules of life. It is important to note that even the simplest organisms living today are far more complicated than our earliest ancestors. No one suggests that cells as we know them emerged directly from primordial chemical reactions. Rather, the quest is to discover simple molecular systems able to replicate themselves and subject to natural selection.

A key starting point is the observation, introduced earlier in this chapter, that the principal macromolecules found in organisms are themselves made of simpler molecules joined together. Thus, if we want to understand how proteins might have emerged on the early Earth, we should begin with the synthesis of amino acids, and if we are interested in nucleic acids, we should focus on nucleotides.