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Science Forum Index » Bio Evolution Forum » Article: A Simpler Origin for Life
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| Robert Karl Stonjek |
 Posted: Wed Feb 14, 2007 8:49 am |
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A Simpler Origin for Life
The sudden appearance of a large self-copying molecule such as RNA was
exceedingly improbable. Energy-driven networks of small molecules afford
better odds as the initiators of life.
By Robert Shapiro
Extraordinary discoveries inspire extraordinary claims. Thus James Watson
reported that, immediately after they had uncovered the structure of DNA,
Francis Crick "winged into the Eagle (pub) to tell everyone within hearing
that we had discovered the secret of life." Their structure--an elegant
double helix--almost merited such enthusiasm. Its proportions permitted
information storage in a language in which four chemicals, called bases,
played the same role as twenty six letters do in the English language.
Further, the information was stored in two long chains, each of which
specified the contents of its partner. This arrangement suggested a
mechanism for reproduction, that was subsequently illustrated in many
biochemistry texts, as well as on a tie that my wife bought for me at a
crafts fair: The two strands of the DNA double helix parted company. As they
did so, new DNA building blocks, called nucleotides, lined up along the
separated strands and linked up. Two double helices now existed in place of
one, each a replica of the original.
The Watson-Crick structure triggered an avalanche of discoveries about the
way in which living cells function today. These insights also stimulated
speculations about life's origins. Nobel Laureate H. J. Muller wrote that
the gene material was "living material, the present-day representative of
the first life," which Carl Sagan visualized as "a primitive free-living
naked gene situated in a dilute solution of organic matter." In this
context, "organic" specifies material containing bound carbon atoms. Organic
chemistry, a subject sometimes feared by pre-medical students, is the
chemistry of carbon compounds, both those present in life and those playing
no part in life. Many different definitions of life have been proposed.
Muller's remark would be in accord with what has been called the NASA
definition of life: Life is a self-sustained chemical system capable of
undergoing Darwinian evolution.
Richard Dawkins elaborated on this image of the earliest living entity in
his book The Selfish Gene: "At some point a particularly remarkable molecule
was formed by accident. We will call it the Replicator. It may not have been
the biggest or the most complex molecule around, but it had the
extraordinary property of being able to create copies of itself." When
Dawkins wrote these words 30 years ago, DNA was the most likely candidate
for this role. As we shall see, several other replicators have now been
suggested.
Source: Scientific American
http://sciam.com/article.cfm?chanID=sa004&articleID=B7AABF35-E7F2-99DF-309B8CEF02B5C4D7
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Robert Karl Stonjek |
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| Tim Tyler |
| Posted: Fri Feb 16, 2007 12:21 pm |
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| Tim Tyler |
| Posted: Sat Feb 17, 2007 1:34 pm |
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Robert Karl Stonjek wrote:
Quote: A Simpler Origin for Life
The sudden appearance of a large self-copying molecule such as RNA was
exceedingly improbable. Energy-driven networks of small molecules afford
better odds as the initiators of life.
By Robert Shapiro
[...]
Quote: Richard Dawkins elaborated on this image of the earliest living entity in
his book The Selfish Gene: "At some point a particularly remarkable molecule
was formed by accident. We will call it the Replicator. It may not have been
the biggest or the most complex molecule around, but it had the
extraordinary property of being able to create copies of itself." When
Dawkins wrote these words 30 years ago, DNA was the most likely candidate
for this role. [...]
Hmm. IMO, DNA was /never/ a plausible candidte for this role.
What Dawkins actually wrote on the subject in The Selfish Gene was:
``The original replicators may have been a related kind of molecule to
DNA, or they may have been totally different. In the latter case we
might say that their survival machines must have been seized at a
later stage by DNA. If so, the original replicators were utterly
destroyed, for no trace of them remains in modern survival machines.
Along these lines, A. G. Cairns-Smith has made the intriguing
suggestion that our ancestors, the first replicators, may have
been not organic molecules at all, but inorganic
crystals-minerals, little bits of clay.''
- Richard Dawkins, The Selfish Gene, page 21.
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