The surface of our planet is populated by living things curious, intricately
organized chemical factories that take in matter from their surroundings and
use these raw materials to generate copies of themselves. The living organisms
appear extraordinarily diverse in almost every way. What could be more
different than a tiger and a piece of seaweed, or a bacterium and a tree? Yet
our ancestors, knowing nothing of cells or DNA, saw that all these things had
something in common. They called that something "life," marveled at it,
struggled to define it, and despaired of explaining what it was or how it
worked in terms that relate to nonliving matter.The discoveries of the twentieth century have not diminished the
marvel quite the contrary. But they have lifted away the mystery
surrounding the nature of life. We can now see that all living things are made
of cells, and that these units of living matter all share the same machinery for
their most basic functions. Living things, though infinitely varied when viewed
from the outside, are fundamentally similar inside. The whole of biology is a
counterpoint between the two themes: astonishing variety in individual
particulars; astonishing constancy in fundamental mechanisms. In this first
chapter we begin by outlining the features that are universal to all living
things. We then survey, briefly, the diversity of cells. And we see how, thanks
to the common code in which the specifications for all living organisms are
written, it is possible to read, measure, and decipher these specifications to
achieve a coherent understanding of all the forms of life, from the smallest to
the greatest.
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