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In my world human(oid)s are not born anymore, they are grown in pods which mirror the conditions of a natural womb.

Children are educated before birth and are "born" as fully mature adults with a standard education ready to join society.

How long would this process take? I assume that artificial growth could be much quicker than a natural 18-20 year period. Could a human be grown in a year? A decade?

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  • $\begingroup$ Some farmers alter the genes in their crops to make them grow more faster and healthier so more resistant to pest, same should applies to animal... $\endgroup$ – user6760 Dec 13 '15 at 2:07
  • $\begingroup$ I don't remember how far babies are matured in artificial conditions in Brave New World. $\endgroup$ – njzk2 Dec 13 '15 at 5:38
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A year? No. Babies already require 9 months in the womb to get to where they get. You're limited because many processes in growth require chemical processes that simply take time. Humans simply aren't cars to be manufactured.

A decade? Now its getting interesting. It is reasonable to assume that a human could grow faster in a "perfect" environment with genes to leverage that perfect environment. Its entierly possible we could reach "fully grown" in a decade. However, the womb would probably have to be adjusted. Many thing a human body needs require things that challenge their motion (so they can learn which muscles are doing what). The humans would be gloriously clumsy unless they got Physical Education as part of their standard education in the womb.

A standard education in the womb you say? That education process might be very daunting indeed. You may be able to physically produce a human in a decade, but you may find it hard to properly educate them that fast.

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    $\begingroup$ You could electrochemically manipulate the brain to induce simulated education. After all, the brain is basically just a over-complicated state machine. $\endgroup$ – Pharap Dec 13 '15 at 10:43
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    $\begingroup$ @Pharap Well, if you isolated only the parts of the brain that are well modeled as a state machine upon which firmware can be loaded, like some over-glorious FPGA, and let the rest atrophy, a state machine you could have. The devil, of course, is in the details. There are many analog behaviors in the brain which cannot be replicated with a state machine, and it is not yet proven that those analog behaviors are completely compensated for by digital means. In particular, the most analog behaviors of all are believed to be the learning mechanisms of creating new synapses. $\endgroup$ – Cort Ammon Dec 13 '15 at 16:21
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Certainly not in a year, no. Growth is limited by multiple things, for example:

  • bone ossification - bones need to both grow laterally and also get ossified. There's a few values for bone growth in children in this paper - basically, a few centimeters a year.
  • skin needs to grow. And the larger a person gets, the greater their surface gets. Think about how long wound healing can sometimes take.
  • neurons in the brain need to grow - your education alone will need several years, and will often have to wait for the growing brain to catch up

You can estimate a lower limit from two scenarios:

  • there's people who never stopped producing human growth hormone, which is one of the factors in determining when children grow. Robert Wadlow's body never stopped growing until he died at age 22 and roughly 270 centimeters. If he was born at around 50 centimeters, that's roughly 10 centimeters a year.
  • the "peak growth velocity" in teenagers, who grow the fastest, is also around 9 centimeters a year

So basically, 10 centimeters a year would be a believable growth rate, meaning from 50 to 180 centimeters, you'd need about 13 years. Under optimal conditions, with great nutrition etc., a decade sounds believable.

However, you might want to keep in mind that this is only lateral growth. The human brain isn't considered fully mature until the mid-20s.

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    $\begingroup$ Something that came to mind as I read your answer is that the isolation could affect brain development. If that's correct, maybe you could elaborate on it? $\endgroup$ – jpmc26 Dec 13 '15 at 4:15
  • $\begingroup$ It’s about 60 cm i the first year, though, if you start with fertilization. Judging from the growth rate in the first 2 years after birth, I estimated a minimum of another 5 to 8 years, but I agree that a few years more seems more realistic since it’s not just length. $\endgroup$ – Crissov Dec 13 '15 at 19:17
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It REALLY depends on what level of technology we're talking about here.

After all, given sufficiently advanced technology, we could "build" a person, atom by atom, to have all the same properties, education, mental and motor functions etc. as if they had developed the normal way over many years.


Let's assume a level of technology that allows us to "develop" the brain in any way we like (including but not limited to: memories, knowledge, motor functions) as the body is growing, but which requires all the normal physical/chemical processes to take place. Albeit in an environment designed to optimise the speed/efficiency of that development.

My guess: 2-7 years

This is based on the fact that the environment you describe (No external interruptions, wholly optimised for and focused on development) sounds very similar to what we call "sleep".

Now, sleep also involves lots of other functions relating to ongoing maintenance/learning/repair which we may be able to eliminate the need for in our growth environment.

But then again, we have almost no idea of *why* humans need to sleep in the first place. So, I would suggest, for every day of "normal" growth, you will need a significant fraction of the time we spend sleeping, 2-8 hours or so, of "Test Tube Development Time". This yields 9%-33% of "Normal Development Time", so 2-7 years for a 20-year-old equivalent.

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  • $\begingroup$ The thing is, babies don’t sleep all the time they’re in their mother’s womb. $\endgroup$ – Crissov Dec 13 '15 at 16:20
  • $\begingroup$ Sure, but that's not the point I'm getting at here. Just trying to provide a hypothetical model applying to a hypothetical civilisation by suggesting the closest allegory we have for all the time somebody spends developing over 20 years. $\endgroup$ – Kaz Dec 13 '15 at 20:30
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18 weeks to 6 or 8 years, but it does not matter

9 months to produce an infant is a long time compared to the initial growth rate of the embryo. At 4 weeks, the embryo is the size of a poppy seed (2 mm long), at 8 weeks, the size of a kidney bean (16 mm head to bottom). During that period, the human increased by at least a factor of 8. This is a growth rate of about 68% per week. At this rate, you are large newborn at 15 week and a full sized adult in under 18 weeks.

So, we have a reasonable lower bound of about 18 weeks and an upper bound of about 18 years. But can we find a better upper bound? Yes we can, Robert Wadlow was the tallest modern man that can be reliably documented. At age 6, he 5'7" and was already taller than his father at age 8. So 6-8 years seems like a better upper bound since people can grow that fast with too much human growth hormone.

Robert Wadlow had health problems and in fact died of medical complications of an autoimmune disease (possibly related to his HGH levels) at age 22. He was reportedly in good health until the final year of his life. His brain was certainly not mature at age 6 or 8, but lets assume that it could be close enough to be considered adult if he had a magical efficient training systems and nanotech to re-arrange brain structures as needed.

So 18 weeks to 6 years. Hypothetically speaking, after all of the needed advances in technology, including nano-tech what could we do?

The answer is simply unknown since we don't have the medical knowledge of the complications of accelerated growth in an artificial womb. Perhaps with nano-technology we could control physical growth, perform the necessary muscle and bone training, deal with the psychological and sociological training. Training the interactions between the brain and eyes, ears, hands, etc. Perhaps it is also possible to teach language, reading, writing, arithmetic, etc. in the womb.

There is a huge gulf between our current state of knowledge and that needed to perform all development in the womb. And there is very little incentive to acquire it.

Parents want to watch their children grow up, play, learn from their environment, etc. I can't image any parent I know desiring to replace this process with an artificial one.

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Human growth is subject to many limiting factors, including the ability of the mother to supply the required nutrients to the foetus, and after birth, the ability of the child to acquire the full range of expected social skills.

A young human is physically small in order to convey the impression of youth to other humans. Since learning to be an adult human takes around eighteen to twenty-five years, that is how long it takes for the human body to mature fully. Size and other physical traits conveys an impression of age to others.

Now, if humans could grow to maturity and be born with all necessary knowledge to be fully functioning adults, as well as be free of the limitations of maternal nutrition, growing such a human in-vitro could occur in a relative short period of time.

In larger mammalian - and dinosaur - species where achieving an adult body-size (of several hundred kilograms to many tons) as quickly as possible is of paramount importance, very high growth rates can be achieved, with newborns achieving maturity within a handful of years, certainly within 5 years or less.

We could therefore expect that with genetic engineering - or some clever artificial stimulation - to remove the limits on pre-maturity growth-rate, a fully mature human could be produced within three years.

I should point out that if humans were genetically engineered to grow that quickly, it would effectively sterilize the population and make them dependent on artificial reproduction. Should a modified human mother become pregnant, her body would not be able to supply the huge metabolic needs that such a foetus impose on her, and a significant or even fatal loss of body mass would likely occur. Should the foetus survive, it would be no better educated than any normal human newborn.

On the other hand, if humans were grown rapidly and educated in-vitro through medical trickery rather than genetic engineering, a natural pregnancy would most likely be possible, with a normal-sized infant being born after the usual period of gestation. It is up to you if the mother would have been educated sufficiently to have the knowledge to handle a naturally-born child.

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