46
4 Life Evolves
4.2 Memory and Function
The grey period between molecules and morphs may have lasted on this planet
for hundreds of millions of years. The scholastic question: which was first – the
chicken or the egg – has mutated in modern deliberations on the origin of life into
the question: which was first – amino acids, assembling into proteins, or nucleotides,
assembling into RNA and DNA (RiboNucleic or DeoxyriboNucleic Acids). The
former are working catalysts, the latter are memory elements – but their relations
are mutual: proteins catalyze the assemblage of amino acids coded by DNA to form
other proteins. John von Neumann (1951), the great mathematical physicist and
mastermind of modern computer architecture, addressing the origin of life from his
standpoint, compared proteins and genes to hardware and software. In computer
technology, the question of which came first does not arise, since both hardware
and software are created and evolved by an intelligent designer. A computer lacking
software can “metabolize” – consume electricity – but cannot do anything else, and,
of course, software without hardware is useless, and would never have been written.
Hardware and software were developed in parallel, enhancing both computational
capabilities and the convenience of programming hard tasks. In later days, when
personal computers became a commodity, this symbiosis became perverse. While
latter-day programmers were economical, trying to extract more output from clumsy
hardware, modern developers bloat operating systems and applications to make outof-date computers obsolete and induce us to buy new ones.
The 1967 Nobel prize winner in chemistry Manfred Eigen reinterpreted von Neumann’s simile in more abstract notions of function and information. In his words
(Eigen, 1971), “function” cannot occur in an organized manner unless “information” is present and this “information” only acquires its meaning via the “function” for which it is coding. Eigen envisaged evolution in the Darwinian sense of
“survival of the fittest” taking place through competitive growth even as early as the
prebiotic stage, by selecting the most efficient cooperative circuits of autocatalytic
reactions that might have become precursors of living matter. Eigen’s definitions are
more precise than von Neumann’s: the carriers of both function and information are
molecules, life’s hardware.
Replicating structures at the boundary between chemistry and life had to be as
simple as possible. RNA is both a short-term memory device and a catalyst. In the
organisms dominating now – eukaryota (Fig. 4.1), DNA base sequences are copied
on short RNA strands, which serve as messengers sent from the cell nucleus to
the cytoplasm where the coded proteins are assembled. However, RNA molecules
are capable of replicating themselves, so they can function both as genotype and
phenotype – what Eigen (1971) calls “self-instruction”. This supported the idea that
the earliest life-like forms were based on RNA (Rich, 1962). Tiny plant pathogens –
viroids – may be a relic of the archaic “RNA world” (Diener, 1989). Viroids are just
RNA strands closed to form a loop. They do not even have a protein coat as viruses
do, but they are capable of replicating, though, like viruses, they need the right
enzyme for this – a protein supplied by the host. Here, too, cooperation between
RNA (or its more primitive precursors of which no evidence remains) and proteins
4 Life Evolves
4.2 Memory and Function
The grey period between molecules and morphs may have lasted on this planet
for hundreds of millions of years. The scholastic question: which was first – the
chicken or the egg – has mutated in modern deliberations on the origin of life into
the question: which was first – amino acids, assembling into proteins, or nucleotides,
assembling into RNA and DNA (RiboNucleic or DeoxyriboNucleic Acids). The
former are working catalysts, the latter are memory elements – but their relations
are mutual: proteins catalyze the assemblage of amino acids coded by DNA to form
other proteins. John von Neumann (1951), the great mathematical physicist and
mastermind of modern computer architecture, addressing the origin of life from his
standpoint, compared proteins and genes to hardware and software. In computer
technology, the question of which came first does not arise, since both hardware
and software are created and evolved by an intelligent designer. A computer lacking
software can “metabolize” – consume electricity – but cannot do anything else, and,
of course, software without hardware is useless, and would never have been written.
Hardware and software were developed in parallel, enhancing both computational
capabilities and the convenience of programming hard tasks. In later days, when
personal computers became a commodity, this symbiosis became perverse. While
latter-day programmers were economical, trying to extract more output from clumsy
hardware, modern developers bloat operating systems and applications to make outof-date computers obsolete and induce us to buy new ones.
The 1967 Nobel prize winner in chemistry Manfred Eigen reinterpreted von Neumann’s simile in more abstract notions of function and information. In his words
(Eigen, 1971), “function” cannot occur in an organized manner unless “information” is present and this “information” only acquires its meaning via the “function” for which it is coding. Eigen envisaged evolution in the Darwinian sense of
“survival of the fittest” taking place through competitive growth even as early as the
prebiotic stage, by selecting the most efficient cooperative circuits of autocatalytic
reactions that might have become precursors of living matter. Eigen’s definitions are
more precise than von Neumann’s: the carriers of both function and information are
molecules, life’s hardware.
Replicating structures at the boundary between chemistry and life had to be as
simple as possible. RNA is both a short-term memory device and a catalyst. In the
organisms dominating now – eukaryota (Fig. 4.1), DNA base sequences are copied
on short RNA strands, which serve as messengers sent from the cell nucleus to
the cytoplasm where the coded proteins are assembled. However, RNA molecules
are capable of replicating themselves, so they can function both as genotype and
phenotype – what Eigen (1971) calls “self-instruction”. This supported the idea that
the earliest life-like forms were based on RNA (Rich, 1962). Tiny plant pathogens –
viroids – may be a relic of the archaic “RNA world” (Diener, 1989). Viroids are just
RNA strands closed to form a loop. They do not even have a protein coat as viruses
do, but they are capable of replicating, though, like viruses, they need the right
enzyme for this – a protein supplied by the host. Here, too, cooperation between
RNA (or its more primitive precursors of which no evidence remains) and proteins