Physical Limits of Cell Division
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Darth Raptor
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Physical Limits of Cell Division
What are the theoretical limits to the growth and regeneration of animal tissue? Assume that respiration, cancer and genetics are non-issues and the cells are not required to actually do anything other than grow and divide. How long would it take to, for example, grow a human from a fertilized egg into a mature adult? IOW, I need to know the reasonable upper-limit to the sci-fi convention of accelerated growth, without resorting to nanotechnology, time distortion or outright magic.
Re: Physical Limits of Cell Division
I am no biologist, but it seems to me that the limit is the amount of mass and energy the mother can provide. A creature like a whale has a gestation period of similar magnitude to that for a human but can produce a huge baby because the mother is huge.
If you could grow the embryo in some form of external machine-womb that can provide more mass, then probably should be able to produce something bigger, however it won't be more mature due to genetic limitations, therefore it would literally be a 'big baby' only [though I notice in your OP you speecify no genetic limiting factor, so your SF culture has ways around that obviously].
If you could grow the embryo in some form of external machine-womb that can provide more mass, then probably should be able to produce something bigger, however it won't be more mature due to genetic limitations, therefore it would literally be a 'big baby' only [though I notice in your OP you speecify no genetic limiting factor, so your SF culture has ways around that obviously].
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Re: Physical Limits of Cell Division
Macrocystis Pyrifera can grow two feet a day, and supposedly has the fastest linear growth rate of anything on Earth.
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Darth Raptor
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Re: Physical Limits of Cell Division
For the record, these are external, mechanical cloning vats. A tentative figure of 4-6 days has been reached, and I want to know if that's conceivable or if I could even go shorter than that.
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Fire Fly
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Re: Physical Limits of Cell Division
Source, go to page 171
The above image is the ideal rate of growth in humans. If you can figure out the rate of growth during early adolescence and maintain that rate of growth from infancy to adulthood, that would give you some idea of what the physical upper limit might be. Keep in mind that there is variation in rates of growth so you could probably push the rate of growth (extrapolated from the above curve during puberty) to a higher number.
If you wanted an even more theoretical number, you could probably derive a formula. This guy has written something on the rate of cancer growth, which would give you the upper limit that you want.
The above image is the ideal rate of growth in humans. If you can figure out the rate of growth during early adolescence and maintain that rate of growth from infancy to adulthood, that would give you some idea of what the physical upper limit might be. Keep in mind that there is variation in rates of growth so you could probably push the rate of growth (extrapolated from the above curve during puberty) to a higher number.
If you wanted an even more theoretical number, you could probably derive a formula. This guy has written something on the rate of cancer growth, which would give you the upper limit that you want.
Re: Physical Limits of Cell Division
Fruit fly cell division in fruit fly embryos is one cell division per cell every four minutes. Mind you, they have much smaller genomes than us (only four chromosomes), but, theoretically, if you GM a human genome to have points of origin all over the fucking place, then there's no reason to think that you couldn't have similar division times.
As humans are composed of about 10 quadrillion cells, you can do the math yourself for going from 1 to there exponentially. I calculate it taking about 52 divisions, or about 208 minutes, so, nearly 3 and a half hours. However, it'd probably take a few days, just so that you can get the important stuff (gastrulation, organogenesis, etc.) out of the way. Once you get to the equivilent of about a 3-4 month old fetus, though, all that you need to do is grow grow grow!
And then be stuck with a creature that is utterly fucked up because it has had no formative experiences.
As humans are composed of about 10 quadrillion cells, you can do the math yourself for going from 1 to there exponentially. I calculate it taking about 52 divisions, or about 208 minutes, so, nearly 3 and a half hours. However, it'd probably take a few days, just so that you can get the important stuff (gastrulation, organogenesis, etc.) out of the way. Once you get to the equivilent of about a 3-4 month old fetus, though, all that you need to do is grow grow grow!
And then be stuck with a creature that is utterly fucked up because it has had no formative experiences.
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Darth Raptor
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Re: Physical Limits of Cell Division
That isn't a problem due to handwavium. Thanks!Akhlut wrote:And then be stuck with a creature that is utterly fucked up because it has had no formative experiences.
Re: Physical Limits of Cell Division
A limit seems to be how how much DNA a cell has and how quickly it can be copied. The quicker the DNA is copied the less likely it can be checked fully and the more errors occur causing mutation and eventually cell death or disfunction.
Some of the faster reproducing Bacteria have a nice trick to speed up their reproduction they start to copy their genome again before the've stopped the previous copy being made. Thus although it takes ~1 hour for E coli to copy its whole genome it can reproduce in 20 minutes in good conditions once its been given a run up to start the process.
I dont know of any multicellular organisms that do anything like this, it might cause the wrong number of chromosomes being passed on in more complex organisms as each chromosome is a different size so it would be hard to ensure the correct ratio of chomosomes are conserved.
Some of the faster reproducing Bacteria have a nice trick to speed up their reproduction they start to copy their genome again before the've stopped the previous copy being made. Thus although it takes ~1 hour for E coli to copy its whole genome it can reproduce in 20 minutes in good conditions once its been given a run up to start the process.
I dont know of any multicellular organisms that do anything like this, it might cause the wrong number of chromosomes being passed on in more complex organisms as each chromosome is a different size so it would be hard to ensure the correct ratio of chomosomes are conserved.
Re: Physical Limits of Cell Division
There definitely appear to be enormous additional limiting factors.
A bacterium under ideal conditions doubling every 20 minutes would go from a cubic micron or so to around 100-kg mass after a factor of 1E17 mass increase, which would be around 56 doublings (2^56) or nominally around 19 hours ... except for limiting factors even in a giant vat of liquid food like an expanding clump of bacteria having other bacteria get in the way, slow the consumption of nutrients, etc.
Clearly all multicellular organisms end up with vastly lesser overall growth rate than the rate of cell division alone for a microbe.
An English Mastiff dog can weigh often even 150+ pounds while reaching either full weight or most of the way to it in their first year of life.
So the genetic engineering could analogously make a 150-pound adult "human" body in a year or less of growth from a single-cell.
Of course, much of the reason humans grow slowly compared to many other animals like dogs is that their growing brains require and obtain full sapient intelligence through long interaction and learning with outside input.
But if that issue is assumed to somehow be avoided, then about 1 year should be considered just an upper limit on the best theoretically obtainable. Perhaps even far faster growth might be possible since it is unlikely that even large dogs are utterly optimized for maximum growth speed.
A bacterium under ideal conditions doubling every 20 minutes would go from a cubic micron or so to around 100-kg mass after a factor of 1E17 mass increase, which would be around 56 doublings (2^56) or nominally around 19 hours ... except for limiting factors even in a giant vat of liquid food like an expanding clump of bacteria having other bacteria get in the way, slow the consumption of nutrients, etc.
Clearly all multicellular organisms end up with vastly lesser overall growth rate than the rate of cell division alone for a microbe.
An English Mastiff dog can weigh often even 150+ pounds while reaching either full weight or most of the way to it in their first year of life.
So the genetic engineering could analogously make a 150-pound adult "human" body in a year or less of growth from a single-cell.
Of course, much of the reason humans grow slowly compared to many other animals like dogs is that their growing brains require and obtain full sapient intelligence through long interaction and learning with outside input.
But if that issue is assumed to somehow be avoided, then about 1 year should be considered just an upper limit on the best theoretically obtainable. Perhaps even far faster growth might be possible since it is unlikely that even large dogs are utterly optimized for maximum growth speed.
