Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?
This is your opportunity to ask questions. No question too simple or too silly.
Culture war topics are accepted, and proposals for a better intro post are appreciated.
Jump in the discussion.
No email address required.
Notes -
Are there any alternative systems to RNA/DNA that can pass on genetic information? I'm not talking about stuff that essentially just uses the central principle and structure of DNA with some of the specifics changed, like XNAs which just use a different sugar backbone, or Hachimoji DNA which just adds on extra base pairs, I'm talking about plausible hypothesised systems that are radically different to what we use now.
One of the most fascinating and out-there proposals I've come across is Graham Cairns-Smith's clay hypothesis, which posits that clay crystals were the first genetic material. The idea here is that crystal growth is a form of self-replication that "reproduces" its arrangement, and can even transmit defects. The pattern is then "passed along" when the crystal breaks (scission) and continues to grow independently from the original crystal. Eventually, a "genetic takeover" of sorts happens, where clay crystals that trap certain forms of molecules to their surface improve their replication and catalyse the formation of increasingly complex proto-organic molecules that eventually take over the original genetic substrate as the new genetic material.
Schulman, Yurke and Winfree in their paper "Robust self-replication of combinatorial information via crystal growth and scission" use the same principles to create a set of DNA "tiles" that replicate its sequence of tiles through crystal growth. Each tile has "sticky ends" that hybridise with each other, and under appropriate growth conditions, complementary sticky ends hybridise, while non-complementary sticky ends are unlikely to interact. The interaction of these sticky ends allows for accurate sequence replication during growth, and once crystal growth has propagated the sequence, these additional layers are then "cleaved" off through mechanical scission.
However, that's the only truly interesting and novel idea surrounding this I am aware of, and I'm not entirely sure if and how this system of replication could achieve a significant level of biological complexity (save for a "genetic takeover" that effectively replaces the original system). I can't help but feel there are probably more such systems that could be posited.
One thing unique to DNA/RNA is that they can be used in two distinct ways: directly copied or interpreted as instructions for building stuff. This is a pretty fundamental property because it allows constructing https://en.wikipedia.org/wiki/Quine_(computing) , with the cell corresponding to the program and the DNA corresponding to the text constant in the program that the cell uses to construct a copy of the cell and also copies and inserts directly. Also it avoids the issue of, how do you replicated a hammer without using a stronger hammer to disassemble it -- instructions for building a hammer don't possess the strength of a hammer and can be examined and replicated easily.
I'm not sure that something that doesn't have this duality can be a somewhat general purpose replicator, not by default at least, and I'd expect any good paper proposing some replicator mechanism to be aware of this.
As far as I can tell, no one has seriously tackled that question in full - I'm not aware of any paper for now that confidently advances a novel system explaining how an alternative replicator mechanism can be interpreted as instructions for building stuff. The way DNA/RNA is translated into building an organism is a fairly convoluted multi-step process and building such a system for any hypothetical replicator is probably very difficult.
Most of the papers I come across are at the very basic level of "how can a sequence of information robustly self-reproduce and transmit its characteristics in a way that Darwinian selection can operate on it", that additional layer of complexity surrounding translation is unfortunately not touched on (either because it's not part of their intention to create a general purpose replicator, or because they can't propose one).
This isn't physical, but consider game of life constructors and replicators. Machines in GOL are turing complete, and can also interact in various ways with their environment, so they can pretty much do anything - and one of 'anything' here is being a quine / selfreplicating. The 0E0P metacell seems cool.
I don't think the original question is fundamentally interesting, tbh - any system capable of universal computation tied to some sort of action will be capable of self-replicating in all sorts of bizzare ways, comparable to turing tarpits.
Hadn't heard about the 0E0P metacell before, reading about it now and it's certainly cool.
I suppose the question was less "would there be other usable self-replication methods" - because the answer's almost certainly yes - and more "has anyone else posited one and would that specific system be capable of significant emergent complexity". The question was asked for completely trivial worldbuilding purposes where specific details are crucial - I have a tendency to get bogged down in detail analysis to an unreasonable degree.
More options
Context Copy link
More options
Context Copy link
More options
Context Copy link
More options
Context Copy link
More options
Context Copy link