How
Many Solutions?
One of the more important experiments concerning the origin of life was performed by Keefe
and Szostak.1 The authors of this paper in Nature searched six trillion random peptides
each composed of 80 amino acids. They were looking for a sequence that could bind the
chemical, ATP. They found four sequences in this large pool with ATP binding activity.
This allows for a direct computation of the molecular knowledge
required for ATP binding. Using equation 2 in chapter 1, molecular knowledge = 3.32 x log
( 6 trillion/4) = 40 bits. Notice, that this is not 40 bits of information because the
proteins that were selected only possessed minimal functionality. These proteins were
subjected to several rounds of selection greatly improving their affinity for ATP.
This experiment provides a direct measurement of molecular knowledge.
It also shows that there are very few solutions to the problem.
Binding a chemical like ATP is one of the functions that many enzymes
possess. So while Keefe and Szostak did not actually find a useful enzyme, they did find a
function than many enzymes require. The 40 bits calculated above are for evolution in a
test tube. What about the soup?
The minimum possible information in a random sequence of 80 peptides is
160 bits (2 bits per amino acid). The odds of such a peptide evolving are one in 1.5 x 1048.
Given that the odds that a random sequence of 80 peptides will bind ATP are only 4 in 6
trillion, the odds of finding a primitive protein on the earth that can bind ATP are
simply the product of the two numbers or one chance in 2.2 x 1060.
Alternatively, the 160 bits needed to construct an 80 amino acid in the soup may be added
to the 40 bits calculated above. The total information is thus 200 bits, and the odds of
this happening are 1 in 2200 or 1 in 2.2 x 1060.
Binding ATP is a simple function. Clay, a simple mineral, binds ATP.
Furthermore, the function by itself does not confer a selective advantage. Thus, ATP
binding is below the threshold of molecular knowledge. This function must be combined with
another function before natural selection will preserve it. To create a functional enzyme
that can be preserved by natural selection quite a bit more knowledge is required. Since
it takes 200 bits to bind ATP, assume that it also takes 200 bits to bind another
molecule. Thus, 400 bits is a more reasonable approximation for a functional enzyme, and
the odds for such evolution are given by 1 time in 2400 tries or a 1 in 2.5 x10120
chance.
The origin of the first enzyme just cannot be explained in this way.
The odds are too poor.
next: The
Evolution of Primordial Knowledge
home: Intelligent Design and the origin of Life
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