So, I have a character that thinks she's invented the cure for aging. And, she has... but not quite how she thought. When administered to adults, it works great; it stops senescence (without causing cancer) and can even restore some youthfulness. (Watson: We don't know yet if it confers biological immortality; check back in a few decades. Doyle: Nope, if you aren't dead by ~90, senescence starts "catching up" to you.)

So, after some testing, she gave it to her whole family, including an eight-year-old daughter and three-year-old son... only to realize to her horror not long after that it doesn't just halt senescence, it also halts maturation.

As someone pointed out to me elsewhere on WB.SE (and which I can no longer find; if anyone knows, a link would be appreciated!), maturation and senescence aren't the same process. So, why might this process be affecting both? Why would a process that halts one necessarily halt the other?

If it helps, my characters aren't human, so if needed I can fudge their biology a little, but nothing too crazy, please. I also have "magic" (which this process uses), but it's fairly well defined / limited and can generally be thought of as equivalent to sci-fi medical nanotechnology. However, there is one major caveat; the process in question is a one-time thing, i.e. it makes some changes and then is "gone".

(The character discovered this process at least in part by studying another person that matured abnormally. Thus, while I could maybe go with the process doing something to the body that causes it to 'snapshot' itself and then continually rebuild to that state, that doesn't fit with how it was discovered. The link can, but doesn't need to, be intractable; it just has to manifest in the early version(s) of the process.)

To clarify, the process stops physical aging. Mental processes should be affected as little as possible. So, in ten years, the thirty-year-old will look the same age or maybe like she's in her early twenties. The eight-year-old daughter will still look like an eight-year-old girl. The three-year-old son will still look like a three-year-old (who, if he hadn't already, may or may not have the whole "continence" thing sorted). Neither will have gone through normal puberty, but the son will be in middle school and the daughter may or may not hate her parents like every other high school student. (Don't get hung up on the social implications.) Both will have adult levels of coordination (ten years practice with a body that isn't changing really helps with that), and the son might be able to ride a bicycle (if he can somehow get one in a suitable size).

Wounds heal at worst normally. The process doesn't need to provide advanced regeneration, accelerated and/or scar-free healing, immunity to cancer, or the like, but it's okay if it does. Basically, the only drawback should be that children remain physically children. (Actually, since this world can very possibly cure cancer, it's probably okay if it might cause much more exciting cancers, so long as the odds are kept in check. That is, the process should cause a 5% risk of getting cancer in 50 years into a 50% chance of not getting cancer in a given month.)

In particular, it does not cause any changes that an adult is likely to notice on a month-to-month basis, and the only reason such changes might be noticed in a child is because children normally grow fast enough that failing to gain weight in a month may (especially for very young children) be noticeable. (Changes in muscle mass or fat mass can still happen, though.)

  • $\begingroup$ Can you add some specific examples of what you mean by "halts maturation"? What kinds of things are halted, and what kind of things aren't. A short list of examples of each, will help a lot. Examples of types of areas where "maturation" changes might exist - physical changes/development? Emotional development? Factual learning (list of elements)? Non-cognitive muscle/neuro skills (such as riding a bicycle)? aging? Damage repair? Healing and injury vulnerability (osteoporosis/Parkinson's/dementia)? Energy/tiredness? Metabolism? $\endgroup$
    – Stilez
    Commented Jun 5, 2021 at 9:53
  • $\begingroup$ After 20 years, does your 3 year old son have the brain size and prefrontal cortex of a 3 year old or a 23 year old. Note the development of prefrontal cortex, brain shape and size could be considered "maturation". $\endgroup$
    – JonSG
    Commented Jun 5, 2021 at 14:41
  • $\begingroup$ @Matthew What is horrifying about discovering that one's children will live longer than usual lives but will not age to adults? Lack of adult size is a small price to pay for longer life. $\endgroup$ Commented Jun 5, 2021 at 16:51
  • $\begingroup$ @M.A.Golding, first, the process only maybe extends life; mostly it extends youth. Second, there is no advantage whatsoever to using it on a child; waiting to use it until after puberty has zero drawbacks... unless you wanted to never grow up, and how many people do you think would really like to be stuck in the body of a three-year-old if there isn't some other benefit? $\endgroup$
    – Matthew
    Commented Jun 5, 2021 at 17:51
  • $\begingroup$ @JonSG, probably the latter. I'm leaning toward it only halting gross physical growth, i.e. stature and proportions, but not more subtle stuff like bone hardening and whatnot. Also, I can't (normally) see a brain and the main point is that the son would still look like a three-year-old. (BTW, characters in the question are just examples.) $\endgroup$
    – Matthew
    Commented Jun 5, 2021 at 17:53

2 Answers 2


Development turns out to be hormonally governed.

One would think science would know all there is to know about the hormones that govern our bodies. Not so. New and important hormones are still being discovered. Example: Asprosin. This peptide hormone that governs fat accumulation and mobilization was discovered in 2018.

Asprosin is a centrally acting orexigenic hormone

Through study of a rare genetic condition in humans – Neonatal Progeroid syndrome (NPS, also known as Marfan Lipodystrophy syndrome, OMIM: 616914), we recently discovered a ~30 kDa fasting-induced hormone, asprosin, which is highly expressed in adipose tissue, and upon secretion, stimulates hepatic glucose release1. Asprosin is the 140 amino acid, C-terminal product of the fibrillin-1 protein (encoded by FBN1). Consistent with the necessity for hepatic glucose release during fasting, circulating asprosin rises with fasting and drops with refeeding in an acute manner, displaying circadian rhythmicity in coordination with the nutritional state...

In your world, the peptide hormone that governs physiologic maturation / senescence had either not been discovered or that function of the known molecule (as fibrillin-1 protein was known) had not been recognized. There are no persons or animals who are naturally mutant for this hormone (as there were for asprosin) because those embryos do not develop in utero and eventually miscarry. The senescence inhibitor is an irreversible competitor of the hormone, tying up the cellular receptors and blocking activity of the hormone.

One does not want normal cellular turnover to be blocked or mucosa and blood cells will not renew themselves, which is fatal. Disposable cells that renew themselves have a shorter clock and are not governed by the long-game master hormone in charge of development and senescence.

This offers a treatment - just as persons deficient in insulin or thyroid hormone can be treated with exogenous hormone, developmentally arrested children can be rescued by exogenous hormone as well. Your scientist isolates and synthesizes the hormone to rescue her children.

Enter malefactor. One might think an overdose of this hormone would be spectacularly lethal, causing rapid aging and death. It turns out that is not the case at all...

  • $\begingroup$ Yeah, I think this is plausible... say, aging/maturation (in the story world) is regulated by some hormone; too little and you grow too fast, too much and you don't grow at all (and such a person would never be born). And it turns out having lots of it also reverses senescence. Plausible? (So... my MC basically discovers this. Note, I don't actually need her to be surprised that it halts maturation; that bit is just flavor text. What matters is that the linkage exists.) $\endgroup$
    – Matthew
    Commented Jun 5, 2021 at 17:59
  • $\begingroup$ @Matthew - well that is the reverse of what I imagined; in normal individuals some is needed and her drug is a blocker so that there is none and progression halts. But either way works. $\endgroup$
    – Willk
    Commented Jun 5, 2021 at 18:19
  • $\begingroup$ Right; I just have a hard time imagining that blocking something would stave off senescence 🙂. At least in my mind, it makes much more sense that there is some magic hormone that keeps the body working, without which "aging" (senescence) happens. Anyway, this fits brilliantly with my "how was it discovered" puzzle. I like to give it a few days to see what else turns up, but I expect this will be getting the green check mark... $\endgroup$
    – Matthew
    Commented Jun 5, 2021 at 19:37
  • $\begingroup$ Well, blocking sex hormones will prevent puberty and arguably also some aspects of senescence. Extreme caloric restriction prolongs life by inhibiting sensescence - possibly by also reducing sex hormones and reproduction. It means thinking about senescence not as stuff wearing out but as part of the developmental program - which is probably correct. This is the high science fiction aspect of your story: childhood development and subsequent senescence are not flip sides of the same coin - they are the same side of that coin. $\endgroup$
    – Willk
    Commented Jun 5, 2021 at 19:49

It affects neuroplasticity. This is going to be a hand-wavy argument, since I'm not a neuroscientist, but you need something to effectively locks the brain in place, since the brain is the thing that changes and in so doing the organism matures cognitively. You can't stop the accumulation of experiences, so to fully "stop maturation" is too broad. If for no other reason than the person would learn new facts. What you want to stop is their ability to change their behaviour patterns after new facts are accumulated. So for instance they might be able to learn everything there is to know about bicycles, but they won't ever be able to read one. I'd peg that on neuroplasticity.

  • $\begingroup$ Uh... maybe this is my fault for being unclear, but this is the exact opposite of what I'm looking for. I actually need to not screw up mental development, but it's physical maturation — physical growth and the onset of puberty — that the process stops. $\endgroup$
    – Matthew
    Commented Jun 4, 2021 at 22:14

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