Vegetative ReproductionCrystalline ancestry: Vegetative reproduction
TranscriptHi. I'm Tim Tyler, this is a video about the crystalline ancestry hypothesis, and the possibility that the first organisms propagated themselves using a vegetative reproduction pattern.
IntroductionThis video builds upon the premise that our most distant ancestors were crystalline entities - and were probably made of clay minerals.Multiple lines of evidence point in that direction - including the fact that crystals are the only known prebiotically-plausible natural structures that are known to copy information with sufficient fidelity to support an evolutionary process. However, if you are looking for support for that premise, this video is not intended for you - and you should probably stop watching now, and instead follow the supplied links to the originoflife.net web site - in order to obtain and peruse the introductory material on this topic - such as the "Seven Clues..." book. Having got that out of the way:
Irregularities and imperfectionsUnder the crystalline ancestry hypothesis, information is be stored and propagated via irregularities in the crystal. For example, here is a model of a screw dislocation - which illustrates one kind of irregularity. Here is a micrograph which shows a real screw dislocation propagating itself in a crystal of silicon carbide. Other types of self-perpetuating dislocation are also common.Such irregularities normally represent imperfections - and are slightly disfavoured thermodynamically. However, fixing an existing irregularity is often more strongly energetically disfavoured, so existing imperfections can be copied and propagated. Also, there are some types of irregularity which are not imperfections from a thermodynamic perspective - such as with some polytypic materials.
DimensionalityOnce you understand that the first living organisms were probably crystalline entities, there is an obvious dilemma relating to how they stored their genetic material - did they use a one-dimensional pattern, or a two-dimensional one?
Two dimensional patternsCrystals which propagate two-dimensional patterns are long and thin. They grow at either end, and then break up when they are too long. Kaolinite is an example of this kind of crystal. Here is a micrograph of Kaolinite. The extruded appearance shows that fault information affecting the exterior form of the crystal is being propagated through the processes of crystal growth. The interiors of these crystals are like sticks of blackpool rock - in that the pattern of information is the same wherever you slice them.
One dimensional patternsCrystals which propagate one-dimensional patterns are flat and more like sheets or ribbons. Information is stored in the sequence of layers that compose them. They grow at their edges. Slicing through such crystals reveals the same pattern of layers at each location - like a unique barcode for the crystal.
1D or 2DFor some time I had favoured the idea that the earliest genomes were probably two dimensional. It seemed to me that several clues supported this possibility - a two dimensional pattern can store more information, and it produces a more interesting phenotype - which potentially includes catalytic grooves down the side of the crystal - which might prove useful for manipulating its environment.If an agent's phenotype is too boring, natural selection will not create and maintain adaptations - and instead a mutational meltdown will occur. However, I had simultaneously been aware that A. G. Cairns-Smith has spent a lot of effort recently studying crystals with one-dimensional patterns. He has been working on barium ferrites and other mixed layer, polytypic materials. Those crystals have some interesting properties to be sure - but I had a hard time considering them seriously as candidate early organisms.
Chemistry and the Missing Era of EvolutionHowever, recently I read a 2008 paper by Cairns-Smith, entitled "Chemistry and the Missing Era of Evolution", which is oriented heavily towards these polytypic materials - and I realised something which I had previously been missing about these flat crystalline structures.
Vegetative reproduction patternI had previously envisaged both long and thin crystals, and thin and flat crystals propagaing themselves via breaking into pieces, and then establishing colonies elsewhere.What I had missed was that the flat crystals were capable of a vegetative growth pattern - which meant that they did not really need to rely on splitting to reproduce - and could propagate via growth alone. That is not really possible for long thin crystals. If they grow, eventually they become too long to support themselves - and must break. When a crystal breaks the broken end may easily be mechanically damaged in the process - possibly introducing mutations. The situation with flat crystals is quite different. These may have multiple growth fronts, not just two. When they break, or tear, it may well be that most of the growth fronts are undisturbed by any damage that occurs at the point of the tear. If the torn area fails to grow back properly, that matters very little, since the rest of the crystal can still expand its intact growth fronts. Also, such crystals don't really need to do much breaking in the first place. They are likely to be stronger - and with multiple growth fronts, are quite capable of exhibiting natural selection between different parts of the same crystal - without any splitting or tearing of the crystal taking place at all. This vegetative growth mode of these types of flat crystal is a feature which makes them quite attractive as candidates for the first living organism. It remains to be demonstrated whether selection on such crystals can be sufficiently strong to overcome natural mutation rates. However, it seems likely that - in a sufficiently secluded underground cave - mutation rates could be made very low - so this may not really be much of an issue. Enjoy.
LinksChemistry and the Missing Era of Evolution - A. Graham Cairns-Smith |