How could I justify shapeshifting into a large-ish monster using hard science? The transformation from man to monster is pretty drastic, so I'm assuming the transformation would at a minimum take upwards of a few days to a week of slow metamorphosis and gorging one's self on thousands of kilocalories worth of raw materials, but is there any way to accelerate the process?

Additionally, what would be the most likely culprit of such a transformation in a hard sci fi setting? Gene therapy? Nanomachines?

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    $\begingroup$ Isn't this a duplicate?! $\endgroup$ – JDługosz Sep 13 '16 at 5:27
  • $\begingroup$ what about being a cluster/giant cacoon of bio-matter that produces many type of bodies per time and has them ready to be controlled one at a time? $\endgroup$ – user24999 Sep 13 '16 at 5:55

I have been fascinated by birds for a while; it is amazing that they appear so big yet have so little mass. Perhaps the transformation is more an illusion and mass is conserved? How about an illusion but the entity uses mass from it surroundings to effect the transformation? It makes for interesting possibilities as to what the individual can appear to transform into...and when you decide on it, is it still an illusion when conforming to science?


This is more of a metamorphosis than shape-changing in the sense of an organism taking on the shape, appearance and form of another creature. To make this transformation scientifically plausible assume the man and the monster are different forms of the same organism.

For the organism to transform this could be triggered by conscious volition where the organism can decide to change and does, hormonally either by taking hormones in pill form or as part of its 'natural' lifecycle.

This approach will restrict the transformation from man into monster by only allowing the monster to be a humanoid creature no bigger than a gigantopithecus. So the transformation will change, say, a six foot man into a nine foot giant ape sized creature. This is not exactly the largish monster the OP requested, but it has been scaled to meet the requirements of hard-science plausibility.

Most the transformation will take place in existing structures possessed by the organism in its normal human morph. Skin, for example, could change colour and form a scaly epidermis, while wattles like those of a turkey might form around its face and head. Additional hair could sprout. Teeth could be replaced by longer and larger teeth rather like baby teeth are replaced and nails grow into claws. Muscles could grow larger and more powerful. This would be effectively a hormone driven muscle building genetically innate program.

The organism would need to consume huge amounts of food and nutrients to bulk itself up into gigantopithecus sized monster. Access to highly functional toilet system would be essential as the organism will need to expel quite large amounts of waste material as it undergoes its metamorphosis. Cleaniness and hygiene should not be neglected. The process of metamorphosis will take weeks as the OP correctly suggested.

A man to monster metamorphosis of this kind would have to be custom built. Presumably, by biotechnologists using highly advanced genetic engineering based on a level of biological knowledge well ahead of 21st century life sciences.


Dedifferentiation of most of the cells of an adult being back into stem cells should do the trick.

See how fast an embryo develops into an infant - nine months for humans, sure, but rats for example will generally take less than a month. Since you are willing to go for nano machines and gene therapy, and this is Science Fiction you are getting into, you could suspend disbelief enough to have a human-sized creature deddiferentiate into a formless yolk/albumin/goo and back into another form within the span of a few days.

Bonus if it involves a huge cocoon structure or a a vat-like artificial womb.


Assuming its voluntary, don't transform - have the monster and 'host' symbiotic. Both of them will die if they're separate too long - ala venom. The 'monster' need not have a fixed form and part of might be attached to the host all the time. That handles the mass issue, and the energy issue.

The human side might have some internal changes, tho nothing drastic enough to make them not look like a baseline. The monster part would be semi inert and re-integrate with the 'human' part of the symbiotic organisms to transform At other times, this would be stored somewhere, like a closet, or say wandering around sewers eating alligators or something

  • $\begingroup$ I don’t get it. How does keeping the monster joined make it small when not “out”? $\endgroup$ – JDługosz Sep 13 '16 at 5:29
  • $\begingroup$ Not big or small. The monster mostly detaches when its not active leaving behind a rudimentary connection. Transformation is reintegration of the bulk of the creature. You could store it in a closet, or have it wandering the sewers, eating passing alligators or something until the host transforms. $\endgroup$ – Journeyman Geek Sep 13 '16 at 5:35
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    $\begingroup$ I do like the symbiotic idea. The symbiont would need to be "stored" somewhere, though, and it would be a creature of its own. Quiiiite cool. Mind if i borrow that idea for a short story? I just fell in love with living space suits.... $\endgroup$ – Andreas Heese Sep 13 '16 at 6:31
  • $\begingroup$ That's kinda why its here ;p $\endgroup$ – Journeyman Geek Sep 13 '16 at 6:32
  • $\begingroup$ I see but the text of the answer needs to be clarified/elaborated. Work the comments into the post, don’t rely on comments to understand the post. $\endgroup$ – JDługosz Sep 13 '16 at 21:43

Let's see...First question should be: how does the transformation work?

I think you'd have to modify the shifters DNA in some way. For that, you could use nanomachines or a simple engineered virus to inject and change the shifters DNA. That might be via injection (virus), or radio signal (machines that were injected earlier) or anything that suits your world.

Since we do not know how human cells react to sudden DNA change, there's no way of knowing what will happen now, but probably it will kill you. Usually, cells can't just change their specialisation and become something else, this ability is limited to stem cells. So the first part should be: change all the cells back to stem cells. Or: change them in a way that all newly build cells become stem cells (remember, your cells split from time to time). But careful now: if you change a cell back to a stemcell, it is possible that it loses its functionality.

At this point, i imagine nanomachines would work best, because they can control the process much better. For example, to transform the lung they would start by "melting" one half of your lungs, rebuilding it and respecializing the cells, while the other half keeps you alive. Then, when the new organ is functional, they'd change the other half. For other organs, e.g. liver, they'd temporarily establish a second "emergency liver" while transforming the primary organ. Since these machines can make cells into stem cells and back, they could use ANY tissue to create ANY organ, so why not a makeshift liver from your second kidney? (btw. this would mean that in the world where shapeshifting is possible via machines, almost all injuries and all sicknesses would be curable).

Overall, i think the process would require quite some time, probably be not painful at all (machines will just shut down the nerves before destroying stuff), and most of all: it needs energy to no end.

Funny thing is: i see no reason why these nanomachines couldn't build you into anything they want, as long as they have the blueprints. But maybe their data storage ability is... quite low, so they can only store one creature-blueprint at a time?

contrary to some other answers i don't think hygiene or .. "waste disposal" would be problems. Your organism is being reconstructed by nano-machines... they can power up your immune system so it kills anything that doesn't belong into your body. If they don't do that themselves.

I do see a problem, though, when it comes to "what does the creature do while transforming". Rebuilding bones, muscles, sinews and everything will take time. So you are definitely not mobile during that time. But if the transformation blocks calory intake, that's a bad thing. So i suspect the process might work around that. First, create a makeshift mouth right on your stomach. Start by transforming head and one arm. When both are done, the user can eat again, so now do the other arm, and remove the makeshift mouth and so on....

I think one might accelerate the process, if you submerge the body in a fluid enriched with nutriments and oxygen. In that case, the body could be supplied from everywhere without paying too much respect to keeping it fed. So the machines might place the shifter in some kind of coma, and just go wild on transforming everything except the brain into liquid goo and back. :)


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