One of the goals in this book
is to investigate how molecular knowledge evolves in biological systems. Because there is
no mathematical definition for knowledge, much of this investigation will be open to
interpretation. To find the molecular knowledge possessed by a chemical like DNA, it is
first necessary to quantify the amount of information. This is true because unlike
knowledge, information has a precise mathematical definition. The scientific definition
for information is very different from the common one. The everyday definition implies
that information should be useful or at least convey some amount of knowledge. The
scientific definition does not make any distinction between useful and useless
information. For example, consider the following sentences:
The brown dog likes to fetch a tennis ball.
Zxrd zgbzbue awfllt jhjzhwzhg zwnzi oppwnnni wyxaz.
If information theory is applied to these two sentences, the results will
indicate that the second sentence contains much more information than the first. Not only
is the second sentence longer, but it contains many letters that are rarely used in
English (z, x, and w). The first sentence contains useful information. The second message
contains no useful information. Yet information theory asserts that the second contains
more information than the first. How can this be?
To understand why, it is necessary to consider why scientists developed
information theory. The theory was developed by an engineer, Claude Shannon, who was
interesting in transmitting information. The second sentence takes longer to transmit than
the first, so it contains more information. This definition is clearly not useful to
biologists studying evolution.
Evolution involves the creation of information that provides a selective
advantage. That is the organism that possesses the new information has an edge over those
that do not. Therefore, the information must be useful. This is why the word knowledge is
preferable. Knowledge implies that information is useful.
In communication systems, information does not have to contain knowledge. In
general, the same cannot be said for biological systems. Information that does not provide
a selective advantage is often lost. Thus, the information found in biological systems
usually conveys knowledge, and this knowledge provides a selective advantage. In
biological systems, knowledge and information are often related, but they are not
necessarily equal. Consider the following two sentences:
I have a dog. His name is Bubba. He is a black lab. He is 13 years old.
My black lab, Bubba, is 13.
Both sentences describe four identical concepts, so the knowledge conveyed by
both is identical. But the first sentence contains much more information than the second.
Because information has a precise mathematical definition, it can be determined rather
easily. In contrast, knowledge will always be open to interpretation. Nevertheless, it is
possible to define molecular knowledge in terms of information. The proposed definition is
as follows:
Molecular Knowledge: the minimum amount of information necessary to enable a chemical (or
group of chemicals) to accomplish some task or to specify some trait. The only stringent
requirement is that molecular knowledge must confer a selective advantage so that natural
selection can preserve it.
Because molecular knowledge is now defined in terms of information,
information theory can be used in conjunction with human insight to calculate knowledge.
The rest of this chapter will explore information and its properties.
Next: Nature
of Information
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