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CNN's World's first living robots can now reproduce, scientists say describes "xenobots"; clusters of stem cells that move around and by this motion occasionally push enough free stem cells together such that they form a new one, at least that's my understanding.

The article says:

"Most people think of robots as made of metals and ceramics but it's not so much what a robot is made from but what it does, which is act on its own on behalf of people," said Josh Bongard, a computer science professor and robotics expert at the University of Vermont and lead author of the study.

"In that way it's a robot but it's also clearly an organism made from genetically unmodified frog cell."

Bongard said they found that the xenobots, which were initially sphere-shaped and made from around 3,000 cells, could replicate. But it happened rarely and only in specific circumstances. The xenobots used "kinetic replication" -- a process that is known to occur at the molecular level but has never been observed before at the scale of whole cells or organisms, Bongard said.

Interestingly the CNN article actually links to the new paper in PNAS Kinematic self-replication in reconfigurable organisms which uses "kinematic" rather than "kinetic".

There is no easy to find Wikipedia article titled "kinetic replication" and the phrase does not appear here in Biology SE nor in Chemistry SE.

I found the 2009 PLOS Computational Biology article Investigating the Conformational Stability of Prion Strains through a Kinetic Replication Model which relates the structural stability of the prion aggregates to the rate of replication.

I also found the 1996 Biophysical Chemistry paper Prionics or The kinetic basis of prion diseases.

And in Journal of Physics A: Mathematical and Theoretical (2015) there is Hidden percolation transition in kinetic replication process.

Nothing jumps out to me as a clear definition.

I found searching for the term to be somewhat confounding because the word "kinetics" relates to the measurement of reaction rates as well as to focus on the actual physical interaction between individual molecules (or organisms) which I think is what's being referred to here. Lots of search results including "kinetic" and "replication" but very few on the combined term.

So I'd like to ask for an answer that explores the term "kinetic replication", hopefully cites a formal definition or at least outlines a generally accepted one, and offers a way to distinguish when the replication of a molecule or an organism is "kinetic replication" and when it isn't.

Question: What is, (and what isn't) "kinetic replication" as it applies to molecules and to living organisms?

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    $\begingroup$ I upvoted because: nice find. I suspect the answer may lie in a whimsical comment coining the term made to a journalist more than a hard-science definition. Google Ngram shows 0 results. $\endgroup$ Nov 30, 2021 at 1:28
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    $\begingroup$ @ARogueAnt. I updated a few minutes ago to add the link to the PNAS article which uses "kinematic self-replication" (a robotics term) rather than "kinetic replication". I'm surprised Ngram didn't at least pick up the two papers I've linked to, do they only search in books or do they also check journal articles? $\endgroup$
    – uhoh
    Nov 30, 2021 at 1:34
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    $\begingroup$ I'm not certain. The reference which leapt out at me was to the superpower of one of the X-Men, hence the whimsey. $\endgroup$ Nov 30, 2021 at 1:44
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    $\begingroup$ It seems to me, having watched the video in the CNN link, that what is being referred to might be autocatalysis: the concept that the product of a reaction can catalyze the same reaction. Auto-proteolysis is a great example. Despite what Wikipedia says, autocatalysis as an explanation for the origin of life long predates 1995. See this video for a great explanation by Manfred Eigen, who received the Nobel prize in 1967 $\endgroup$
    – user338907
    Dec 2, 2021 at 22:52
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    $\begingroup$ @user338907 excellent video and explanation, thanks! $\endgroup$
    – uhoh
    Dec 3, 2021 at 0:28

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The short answer to your main question: "what is a kinetic replication?", is that all known mechanisms of replication can be labelled kinetic because they are dynamical processes involving molecular motion.

The second and the third paper you cited use the term "kinetic" in the context of chemical kinetics. That is, studying the reaction rates of many (different) chemical molecules. I would assume that most biological papers would use the term "kinetics" in a similar context (bio- chemical kinetics).

However, the first paper you cited talks about something different. The term they use is "kinematic" which is deliberately intended to describe a unique phenomenon pertaining to physical motion of cell structures.

See the significance statement of the paper:

Some molecules also replicate, but by moving rather than growing: They find and combine building blocks into self-copies. Here we show that clusters of cells, if freed from a developing organism, can similarly find and combine loose cells into clusters that look and move like they do, and that this ability does not have to be specifically evolved or introduced by genetic manipulation.

In classical physics, kinematics pertains to study of motion and this paper also refers to physical motion of cells.

Chemical kinetics is also based on movement of molecules but these movements can also cause new chemical bonds to form. Thus the changes do not merely occur in spatial co-ordinates. The PNAS paper authors present an example model of self perpetuation (also called replication) that is primarily based on spatial reorganization. Their results do not talk about any chemical changes occurring in the cells. Perhaps they do occur (my guess; like change in expression of cell adhesion molecules) but the overall mechanism still appears to be mostly physical.

Coming back to your original question. I don't think anyone really uses the term "kinetic replication" and that's the reason you could not find any references to it. The CNN reporter indeed made a typo when referring to the PNAS paper.

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  • $\begingroup$ Luckily I'm at home at the moment because when I got to the last sentence I laughed out loud. :-) Well if a CNN typo caused me to learn some new things, then I can be happy about it. I'll need one more cup of coffee before I can take in the full extent of your answer, but I can say right now thank you for taking the time to write such a clear and comprehensive answer! $\endgroup$
    – uhoh
    Apr 3 at 4:06

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