The path to homo sapiens sapiens (us) was a precarious one. It could easily
have turned out otherwise!
The DNA molecule is wondrously designed to further the process of evolution (descent
with modification based on mutations and tested by differential reproductive success).
Could we have designed such a system ourselves?
From The Medusa and the Snail by Lewis
Thomas:
"If our kind of mind had been confronted with the problem of
designing a similar replicating molecule, starting from scratch, we'd never have
succeeded. We would have made one fatal mistake: our molecule would have been
perfect. Given enough time, we would have figured out how to do this, nucleotides,
enzymes, and all, to make flawless, exact copies, but it would never have occurred to us,
thinking as we do, that the thing had to be able to make errors.
"The capacity to blunder slightly is the real marvel of DNA.
Without this special attribute, we would still be anaerobic bacteria and there would be no
music. Viewed individually, one by one, each of the mutations that have brought us
along represents a random, totally spontaneous accident, but it is no accident at all that
mutations occur; the molecule of DNA was ordained from the beginning to make small
mistakes.
"If we had been doing it, we would have found some way to correct
this, and evolution would have been stopped in its tracks."
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