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in RNA molecules, for example, new structures suddenly appear abruptly if enough muta­

tions are present. These so-called neutral pathways in RNA structures can be thought of as

follows: As long as the mutation does not change the base pairings, it changes the stability

of the RNA only slightly. An identical base pairing, i.e. the replacement of an A-U pair by

a C-G pair, is called a “conserved substitution”. In addition, a structure can simply

“endure” a series of minor mutations (i.e., remains stable enough) until eventually the

stability is no longer enough, and then the RNA suddenly refolds. This then separates one

RNA structure from the next via such a neutral pathway. So each pathway accumulates

many neutral mutations. A similar thing happens when you look at protein structures in

three dimensions (it’s just more complex): Again, I can have a whole bunch of mutations

associated with the same structure (“neutral path”), but eventually I have so many muta­

tions that my structure suddenly flips. In evolution, this new structure only survives if it is

beneficial to the prevailing environment. This has also led to a specific perspective on

evolution: “punctuated equilibrium” according to Stephen J. Gould (1989) assumes that

there are always “hot phases” of change in a population, because then suddenly mutations

are no longer neutral and lead to new structures that are, among other things, advanta­

geous. After that, everything remains similar for a long time (equilibrium). In reality, how­

ever, more and more neutral mutations accumulate in all structures until suddenly, due to

decisive mutations, one or more RNA or protein structures “tip”, i.e. change rapidly. This

is followed by another period of quiescence in which mutations accumulate but no struc­

tural change occurs. This model explains at least relatively much about the predominant

observed pattern of evolution. Over time, then, there has been no directed “higher develop­

ment” in evolution, but rather the genetic material in the various populations continues to

change through complex processes over time, while other populations die out altogether

and new ones emerge.

Nevertheless, the overall effect on life as a whole in the 3.5 billion years since its origin

has been considerable: about 450 million years ago, i.e. since the upper Silurian or lower

Devonian age, higher (eukaryotic, see glossary) life spread to the land and shortly after­

wards to the air. Over time, life has formed more and more species on average and the

biomass has also grown more and more despite several mass extinction events.

The still numerically clearly dominant bacterial (prokaryotic) cells have consolidated.

It can be shown that today’s enzymes have been very well optimized in their catalytic

activity. The same is true for metabolic pathways that have led to more and more, increas­

ingly complex metabolites and have also become more and more efficient and robust.

However, this then applies to the overall trend, across all bacteria (prokaryotes, i.e. eubac­

teria and archaebacteria). For a single species, specific environmental adaptations domi­

nate, interspersed with neutral mutations, and the set of adapted mutations keeps changing

as the environment changes. So, up close, variance and neutral change dominate. By the

same token, evolution would never repeat itself the same way even when restarted, but

would always find new species (or “solutions” if you will). Moreover, one must keep in

mind that for every species alive now, there are 1000 others that are already extinct.

10.1  A Brief Overview of Evolution from the Origin of Life to the Present Day