26. Origin of Life on Earth
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       The Problems of Organized Cells

So far we have glibly bypassed a massive problem. How do we get from the Haldane soup to even the simplest fermenting bacterium?

A long, long step exists between amino acids, sugars, and nucleosides, and simple cells of the Fig Tree type, and this is the step about which we know least.

From the short time span involved from the formation of the planet to the development of these simple photocells, it can be argued that the problem must be simpler than we think.

An equal time span occurred from protocells to eucaryotes, and we think we have a good idea as to how this change came about. The difficulty is that we have visible evidence for this latter process, in microfossils and living survivors, but no such evidence has survived for the evolution of protocells.

This is a continual problem in evolutionary history, the erasure of the older record. Survival on this planet is based on efficiency, and there are no museums of unsuccessful types.

Even among the bacteria, we do not have samples of all of the ancestral chemistries, only those that enabled their possessors to get along in odd corners where their more "advanced" eucaryotic competitors could not survive.

We should not view the present-day bacteria as representative of the ancestors of the main stream of development, but rather as the "oddballs."



Nevertheless, we do have this record to study from the protocells of the Fig Tree deposits to the first eucaryotes. For periods earlier than this, we have nothing at all.

We know how the planet began, and how this first phase in the evolution of life ended. The gap between must be filled by imagination tempered by the results of laboratory experiments.

The chemical problems to be overcome are many.

How were polymers of proteins, nucleic acids, and lipids formed in an aqueous environment, when polymer formation requires the removal of water and is thermodynamically nonspontaneous?

How were the first reacting systems isolated from their surroundings to avoid a lethal dilution and cannibalism by other competing systems?

How were the chemical reactions of a protocell integrated into a coherent and efficient "metabolism" that would increase its chances for survival?

And finally, having achieved all these things, how did the successful protocell find a way of preserving its gains and passing them on?

These are the next questions that we must try to answer.


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