- Test of Cairns-Smith’s ‘crystals-as-genes’ hypothesis - Faraday Discussions (RSC Publishing)
- Account Options
- Looking for other ways to read this?
The latter is important because it means we don't have to imagine a coupled system of nucleic acids and proteins magically popping into existence all at once—the catalytic role of the proteins could originally have been filled by the nucleic acids themselves. However, there are also some problems with the conventional view, which are discussed in detail in the book but which are not of particular interest here. According to the genetic takeover theory, the original replicators were not biochemicals at all, but instead were minerals—clays, to be specific.
A substantial portion of the book is spent explaining the chemistry of clays, so that the reader can understand why replication in clay is plausible.
Test of Cairns-Smith’s ‘crystals-as-genes’ hypothesis - Faraday Discussions (RSC Publishing)
Here's my quick summary. Clays can grow by accretion, and can contain information in the form of defect patterns. Replication occurs because the pattern of defects on the growing face propagates itself into the succeeding layers. What's more, it is well known that surfaces can act as catalysts, so different defect patterns should be able to catalyze different reactions in the chemicals that flow over the surface. It is in this way that the first biochemicals would have been formed.
If, for example, a particular defect pattern catalyzed the formation of a protective organic coating for the clay, then that pattern would possess an evolutionary advantage over other defect patterns. As the clays formed more and more complex biochemicals for their own purposes, the biochemicals became capable of replicating on their own, and did so, superseding the old clay-based replicators.
This was the genetic takeover. As an aside, it is interesting to wonder whether the clay-based replicators were necessarily completely superseded—maybe we could find some of them still alive as mud on the sea floor somewhere.
- Genetic Takeover And The Mineral Origins Of Life!
- Functional Analysis in Mechanics.
- Genetic Takeover And The Mineral Origins Of Life by A.G. Cairns-Smith.
- Navigation menu.
- Account Options!
Here is Cairns-Smith's own summary of the theory of genetic takeover. Similarly, in a genetic takeover, the primary genome creates an environment in which evolution of the secondary genome can occur more rapidly in certain directions. There is another interesting analogy, with the process of endosymbiosis: In endosymbiosis information can flow between the genomes of the organisms involved, as they "compete" with one another to perform each other's functions.
- Genetic takeover and the mineral origins of life /.
- Getting Started with S-PLUS 6 for Windows.
- Genetic Takeover and the Mineral Origins of Life | NHBS Academic & Professional Books.
- Handbook of Chemical Reactor Design, Optimization, and Scaleup (McGraw-Hill Professional Engineering).
- Quotable Quote by Cairns-Smith.
- Membrane Contactors: Fundamentals, Applications and Potentialities.
- Clomiphene - A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References.
Unfortunately, horizontal gene transfer between endosymbionts and their hosts can occur by the direct action of their DNA being physically mixed together, partly obscuring the effect. It appears that a likely result of endosymbiosis will be one of the participants completely absorbing the functionality of the other, through a mixture of horizontal gene transfer and copying of the supplied technologies. There have not been any significant changes to the genetic substrate for billions of years. However there are currently "various indications" that a genetic takeover is imminent: The rise of human culture 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 via nucleic acids.
However very recently, various new methods of transmitting information to descendants has 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. These mechanisms are usually though of as transmitting "cultural" information - but there is no fundamental distinction between genetic information and cultural information in this context.
Until human beings came on the scene "cultural" transmission of information existed - but was very limited in volume. 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 could be extremely far-reaching. Nucleic acids are a form of molecular nanotechnology - as such they are a compact, concise and surprisingly reliable form of information storage. It has been sufficient to act as the primary information-storage medium for life for the past four billion years.
However, currently, new storage media are frequently used in preference to DNA for a number of reasons: Accessibility Today reading and writing information in nucleic acids is a laborious rigmarole. Sequencing a single human genome took years to complete. Nucleic acids were "designed" to be replicated - but not written to.
Modern information storage demands the ability to be easily modified when circumstances dictate this is appropriate;. Nucleic acids are long, stringy molecules.
While it may be possible to grab them at a specific point, they're not designed with this in mind. They are like a tape - and lack the random access features you would get with say a disc. Even copying a single nucleic acid chain is a tedious and slow process. In principle it might be possible to break it up and parallelise the process - but for rapid access to the information, it is not currently an attractive option;.
Looking for other ways to read this?
Nucleic acid chemistry is effectively dependent on the presence of liquid water, and a number of admittedly fairly common organic compounds. There is no fundamental reason why life should no exist at very low or high temperatures;. Nucleic acids are essentially one-dimensional molecules. In three dimensions they tend to coil up. Random access considerations mean that future storage media are likely to be two- and three-dimensional.
Human cultural information can be expressed in phenotypes in many diverse ways. It can control the design of automobiles, or result in animated images or music. Its volume can be very large, and it can be replicated with high fidelity. Human culture is subject to conventional Darwinian evolution - but is also subject to Lamarckian processes, and to intelligent design.
These demand an information-storage medium with an ability to write data conveniently. Today's electromagnetic, magnetic and optical storage devices seem likely to be replaced by nanotechnological devices - or possibly mechanisms based on individual atoms in crystalline lattices. There may well eventually be advantages to the new media in terms of stability, expense, access speed and the ability to modify the information. Some of these were not significant criteria when the current genetic machinery was selected, but they are important in storage media today.
If the original genetic takeovers were driven by the ability to direct new technologies e. DNA is currently only used to influence phenotypes by directly controlling the synthesis of some twenty amino-acids. The resulting protein machinery is very flexible and can direct a large number of other types of chemical reaction. Despite this, nature has failed to master some relatively simple and obvious mechanical technologies - for example, notoriously nature makes very little use of the wheel. At the moment it appears that a whole raft of new technologies is driving the adoption of new genetic materials.
Most programmable computers are currently constructed from specifications that are not stored in DNA. Also, DNA appears ill-placed to directly control the synthesis of the important Fullerene molecules.
https://vefecchandhabi.tk The significance of these molecules may be primarily structural - or they may eventually come to play important information-processing roles. Either way it appears that the relatives of diamond and graphite are likely to be important components of the organisms of the future because of their unique chemistry. It appears that genetic takeovers are a fundamental - though currently little-understood - aspect of the process of evolution. The fact that the takeovers near the start of life are very distant from us has obscured their significance as evolutionary events.