CHAPTER 26 | ASTROBIOLOGY: LIFE ON OTHER WORLDS 583
the rungs, providing instructions to guide specifi c chemical
reactions within the cell.
Th e instructions stored in DNA are genetic information
passed along to off spring. DNA instructions normally are
expressed by being copied into a messenger molecule called
RNA (ribonucleic acid). Th e RNA molecule travels to a loca-
tion in the cell where its message causes a sequence of
molecular units called amino acids to be connected into large
molecules called proteins. Proteins serve as the cell’s basic
structural molecule or as enzymes that control chemical
reactions.
Th e DNA molecule reproduces itself when a cell divides so
that each new cell contains a copy of the original informa-
tion. A sequence of DNA that composes one instruction is
called a gene. Genes are organized into long coiled chains
called chromosomes. Th e genes linked on one chromosome
are normally passed on to off spring together.
To produce viable off spring, a cell must be able to make cop-
ies of its DNA. Surprisingly, it is important for the continued
existence of all life that the copying process includes mistakes.2
3
Th is chapter is concerned with the origin and evolution of life as
it is on Earth, based on carbon, not because of lack of imagina-
tion but because it is the only form of life about which we know
anything.
Even carbon-based life has its mysteries. What makes a lump
of carbon-based molecules a living thing? An important part of
the answer lies in the transmission of information from one mol-
ecule to another.
Information Storage and Duplication
Most actions performed by living cells are carried out by mole-
cules that are built within the cells. Cells must store recipes for
making all those molecules, as well as how and when to use
them, and then somehow pass the recipes on to their off spring.
Study DNA: The Code of Life on pages 584–585 and
notice four important points and seven new terms:
Th e chemical recipes of life are stored in each cell as infor-
mation on DNA (deoxyribonucleic acid) molecules that
resemble a ladder with rungs that are composed of chemical
bases. Th e recipe information is expressed by the sequence of1
Must science and religion be in confl ict?
Science is a way of understanding the world
around you, and at the heart of that under-
standing are explanations that science gives
for natural phenomena. Whether you call these
explanations stories, histories, hypotheses, or
theories, they are attempts to describe how
nature works based on evidence and intellec-
tual honesty. While you may take these expla-
nations as factual truth, you can understand
that they are not the only explanations that
describe the universe.
A separate class of explanations involves
religion. For example, the Old Testament
description of creation does not fi t well
with scientifi c observations, but it is a way
of understanding the universe nonethe-
less. Religious explanations are based partly
on faith rather than on strict rules of logic
and evidence, and it is wrong to demand
that they follow the same rules as scientifi c
explanations. In the same way, it is wrong
to demand that scientifi c explanations take
into account religious beliefs. The so-called
confl ict between science and religion arises
when people fail to recognize that science and
religion are different ways of knowing about
the universe.
Scientifi c explanations are very compelling
because science has been very successful at
producing technological innovations that have
changed the world you live in. From new vac-
cines, to digital music players, to telescopes
that can observe the most distant galaxies,
the products of the scientifi c process are all
around you. Scientifi c explanations have pro-
vided tremendous insights into the workings
of nature. Many people are attracted to the
suggestion, made by evolutionary biologist
Stephen Jay Gould and others, that religious
explanations and scientifi c explanations should
be considered as “separate magisteria.” In
other words, religion and science are devoted
to different realms of the mystery of existence.
Science and religion offer differing ways
of explaining the universe, but the two ways
follow separate rules and cannot be judged by
each other’s standards. The trial of Galileo can
be understood as a confl ict between these two
ways of knowing.Galileo’s telescope gave him a new way to know
about the universe.26-1
The Nature of Scientifi c Explanation