Thanks again to those who have replied. I received this comment from Keith
about my anaolgy of the two computers:
> The problem is that in your analogy we have a pre-existant computer,
> into which a program is loaded. Without the program, the computer is
> complete. DNA and organisms are not like that. Each requires the
> other. Without the DNA, the cell would not develop. Without the
> cell, the DNA has no vehicle.
The analogy was my own, not quoted from the book. I am happy to accept
criticism of it. In the analogy, however, the pre-existant computer stood
for a pre-existant mother, the binary string was the DNA of her newly
conceived embryo. What if each of the computers interpreted the (identical)
binary strings as instructions for building a copy of themselves (assume the
computers have devices attached to them that will let them do this). Since
the computers are different, they will interpret the string differently, and
the child computers will be copies of their parents rather than identical to
I also received this reply from Laura Adamkewicz:
> I would suggest that DNA does have independent meaning as
> proved by the fact that one can move a piece of it to a
> different organism, where the DNA will "mean" the same
> thing. That meaning is present whether or not the DNA is in
> use and is inherent in its sequence.
As pointed out to me by Andrew Rambaut, species are not independent:
> That is they have alot in similarity due to common descent. Also there
> is the problem of developmental constraints - once a particular gene
> becomes locked into a particular developmental function it becomes
> difficult to change radically because an error in development is usually
> fatal (or zero fitness).
Like language, which has a commonly agreed meaning among its users but no
inherent meaning on it's own (I would be interested to hear serious
objections to this), the relationships among species will account for common
interpretations of DNA sequences. This does not change the fact that the DNA
means nothing without something that 'knows' what to do with it.
I am not suggesting that the phenomenon of two species with the same DNA
actually occurs in nature, I'm saying that the relationship between
evolution and DNA is less direct, and more complicated, than it may appear.
Also, I am aware that a program written for a PC would not be likely to run
on an Apple Mac.