Genetic Takeover

Introduction

Introduction

The idea is perhaps best explained by a diagram:

Here, G1 is the primary genetic substrate, and G2 is the secondary one.

Arrows within the organisms running from genotype to phenotype indicate paths of genetic expression.

A simple organism with genetic substrate G1 initially produces substance G2 as a component of its metabolic processes.

G2 is inherited - and it eventually comes to carry heritable information.

Gradually, G2 completely displaces G1 as the primary genetic material for the organism.

The principle of genetic continuity

Consequently, it seemed as though primitive genetic materials would be related to the modern genetic machinery in such a way that the two could be linked by a series of gradual changes.

The mechanism of genetic takeover allows for the possibility that a secondary genetic material can arise not as a modification of the primary one, but rather from molecules synthesized under its control.

Takeovers are common

The many discontinuities in the fossil record are caused by invasions - where organisms are displaced by organisms that have evolved elsewhere. We can see similar events going on today in New Zealand and Australia.

Clay minerals

This resulting liberation allowed Cairns-Smith to propose that the first living organisms were in fact extremely different in their construction from the type of organism we are now familiar with.

In fact, he proposed that our ultimate ancestors were actually clay mineral crystals.

Regardless of whether his theory of Crystalline Ancestry is correct, it still seems highly likely that multiple genetic takeovers were involved in the origin of today's genetic machinery.

Evolution of the genetic substrate

Initially the second genetic material is not critical to the organism, and may thus be subject to variation and natural selection - without changes necessarily resulting in a non-viable organism.

A booster rocket

A sceptic might argue that this is just as difficult as the secondary genetic material arising from scratch out of inorganic matter - but this is not the case.

The second substrate can be a thermodynamically unlikely object, whose very existence would be implausible in the absence of an existing evolutionary process and natural selection. So, the first genetic material can play a vitally important role in the production of its sucessor.

In much the same way that a spaceship traveling into space requires a booster rocket to get it out of the atmosphere, so early life required a boost in order to get off the ground in the first place. This is because the modern genetic mechanisms are too sophisticated to plausibly form under pre-biotic conditions.

In the same way that a spaceship discards its booster rocket as dead weight, so the initial genetic machinery appears to have been completely discarded now that a superior, high-technology alternative has been developed.

Information transfer

Essentially, the primary genome provides the environment in which the secondary genome evolves.

Since the components in the original phenotype are replaced gradually, there is likely to be a functional relationship between the original components and their replacements - since the elements are replaced one at a time.

It is important to emphasize the fact that there can be ways to transfer information from the old genetic medium to the new one - even if there is no specific apparatus that can read from the old medium and write to the new one.

The idea that the new life is necessarily the mortal enemy of its ancestors not necessarily correct - in a very real sense, some of the heritable information of the ancestors can survive in their descendants.

Significance

We do not know exactly how many genetic takeovers there were, but it seems likely that there were several - and that they were critical milestones on the road to modern orgainsms.

Despite the pivotal nature of genetic takeovers, their significance is not recognised by most modern literature on the subject.

The modern takeover

There have not been any significant changes to the genetic substrate for a very long time - however there are currently a number of indications that a genetic takeover is imminent:

An examination of the communication of high-fidelity information between organisms and their descendants reveals that almost all the information transmitted over the history of life on earth has been stored in nucleic acids.

However very recently, various new methods of transmitting information down the generations have arisen. These have the high-fidelity of replication necessary to be able to support evolutionary processes, and are capable of transmitting large volumes of information - and this information persists via a copying process and is inherited from one generation to the next.

Until human beings came on the scene "cultural" transmission of information existed - but was much more limited. For example, a bird's offspring may inherit the songs of their parents - but probably only a small number of generations will pass before it is not possible to identify the parents from the songs of their descendants.

By contrast, human beings have brought with them the written word and - more recently - books, CDs, DVDs and other optical, electro-magnetic and electronic storage media. The result is a large volume of heritable, high-fidelity information which is not transmitted through nucleic acids.

The ultimate effect of these types of new information storage media on biological evolution seems likely to be extremely far-reaching.

The possibility of a modern genetic takeover has been pointed out by Richard Dawkins and Hans Moravec.

I have discussed the possibility of a modern takeover in more detail elsewhere - in my video/essay Memetic Takeover.

Conclusion

The fact that the takeovers near the start of life are very distant from us has obscured their significance as evolutionary events.

Whenever evolution develops new and superior information-storage devices there will be an immediate "pressure" for genetic information to migrate into them. This process will continue for as long as superior information-storage technologies exist.

The information storage aspect of the medium will probably become increasingly abstracted from the replication mechanism, and from the phenotypic expression of the information it carries - so in the future, upgrades to the materials that carry heritable information seem likely to be relatively painless.

In the light of the fact that we may now be facing the first genetic takeover for several billion years, some interest in the mechanisms behind them would appear to be appropriate.

Enjoy,

References

My original esssay on genetic takeovers;

An esssay on genetic takeover types;