#undertale science

Where potential mates of their own species are rare, animals might hybridize with closely related species. Furthermore, animals might make hybrids if they're compatible species kept in the same enclosure (e.g., lions and tigers in zoos). In birds when one species parasitically lays its eggs in the nests of another species, the offspring might imprint after its host parents in looks or song, and so only be interested in birds that look or sound like its host parents.

All these things likely happened when monsters were sealed underground. While it’s unclear if different monster breeds interbred before the war, given monsterkind’s massive casualties it’s likely monsters’ options within their own breed were limited. (This would surely be especially true for monster breeds that were rare to begin with.) Staying underground, especially if they all stayed in just one city for a long time, would also work like captive conditions. Furthermore, the devastation might have meant a whole lot of orphans, which might have been raised by different breeds. Such orphans might, like the parasitic birds, prefer breeds like the ones they were raised by. It’s certainly clear monsters have variable preferences and can imitate other monsters (e.g., Papyrus catching a thrown stick in his mouth)/have variable behavior, after all.

Biological Problems

For some breeds, even if hybridizing is possible it would likely cause health problems. This is especially obvious for fire monsters, such as offspring of the Sans X Grillby ("Sansby") pairing. Though skeleton monsters are apparently1 insensitive to cold, it's unclear whether they're insensitive or immune to heat too. Fan works often assume Grillby's fire is painfully hot, and becomes much hotter when angry. While (dry, human) bones can withstand greater temperatures than human flesh without (visible) damage, being on fire constantly might be a problem. Even if the hybrid children can withstand it, it's possible (and more likely) that they might hurt themselves from the higher temperatures if they ever get angry.

Pain can make people easier to anger, so being burned by their own flames might cause a self-destructive feedback loop of pain and burning. If they can't quickly heal burn markings from such events, they might become anxious about it, akin to obvious scars or burn wounds.

Environmental Unsuitability

Environmental unsuitability is also a problem. While a hybrid's parents might be well-suited to distinct environments, the hybrid may be unsuited for either or require unpredictable intermediate environments.

For example, the fish monster Undyne is vulnerable to heat stroke/dehydration when travelling through the dry, hot caverns of Hotland; Alphys is not. Evidently travelling through Hotland is enough of a danger to Undyne that Alphys installed a water cooler for her halfway to her lab, even though Alphys' lab is only a few screens into Hotland. While Undyne says she dislikes "snow", she's evidently not in danger standing outside Papyrus's house indefinitely. This might not be true for Alphys: while some fish can live in cold water, reptiles either die or hibernate in cold environments like Snowdin.

A hybrid child of the two might do well in an intermediate environment (e.g., hot but humid, like south Florida) or take after one or the other unpredictably.

Some assume Undyne can breathe underwater through gills; what if the child prefers most of their body to be dry but needs to keep their gills moist? What if the child prefers dry, but not hot, environments? With such a potential blend of preferred environments, they all might need custom rooms (e.g., humidifiers, pools) in one house.

Most dangerously, what if Undyne can breathe water through her skin, but a reptile-skinned but otherwise fishlike child cannot? One work, Scramble Saga, suggests Undyne sleeps in a water-filled bathtub rather than a bed. If a helpless baby that can't breathe underwater is put in a tub-crib, the baby might drown. The child might drown, too, if Undyne is playing boldly and aggressively in the water and mistakenly assumes the child can breathe underwater.

Psychological Problems

No Horns

(The picture is based on goat skulls; notice they don't have horns. Picture modified from here.)

In goats, horn buds don’t grow directly from the skull, but from a specialized patch of skin. Only later do they start to merge to the skull.

Assuming Boss Monsters’ horns grow like that of goats, a Boss Monster-skeleton hybrid might not have horns. (Many such fanchildren have no skin, after all.) While many monsters do not have horns, this might still make the fanchild self-conscious about not having horns. (Perhaps similarly to Kris of Deltarune, though Kris is a human.)

The Problems of Papyrus x Mettaton

“Us ghosts spend our whole lives looking for a proper vessel. Slowly, slowly, we grow closer to our new bodies... Until one day, we too may become corporeal beings. Beings able to laugh, love, and dance like any other...” - Mad Dummy

It is unclear whether ghosts’ desire for vessels (or “bodies”) is biologically or culturally driven. Either way, hypothetical fanchildren of Papyrus and Mettaton are likely to be dissatisfied with their bodies.

LordLaharl’s Vassal made a convincing point that Papyrus may have body dysmorphia issues. The Wikipedia article on the subject suggests part of the variation in body dysmorphia issues in the population (or “heritability”) can be explained by genetics. If this is true, and also true for monsters, a Papyrus x Mettaton child could have twice the body issues of either parent.

It’s unclear whether the child would be born/the equivalent of born a ghost fused with a skeleton body, a ghost possessing but not fused with a skeleton body, or be born separately as a ghost body and a skeleton body. If the Papyton child has a handy skeleton body from birth/the equivalent of birth, the child might not develop ghostly psychological problems, as the child could do normal non-ghost things with it.

Related Reading

Inter-Species Socialization

Do Monsters Have Instincts?

However, it’s also possible its growth is partly based on skeleton “genes”, for lack of a better word. If the two breeds grow at the same rate, the effects would cancel each other out, and the growth rate would be normal.

Still, if the growth rate of each is different (i.e., if Boss Monsters take much longer to mature than skeletons) it would be hard for either to figure out when to expect developmental milestones. What if Asriel made his first magical bullet at sixteen, but Sans made his at four?

Active Vessel

(Diagram supposing the child doubles the drainage rate and connections with Toriel, while not draining Sans)

This is the most dangerous possibility, not to the child but to the parents. This supposes the flow of SOUL power is something like mammal pregnancy, where a complex chemical interchange keeps the interests of the mother and embryo in balance.

If unable to draw the usual amount of SOUL power from one parent, the hybrid's body/SOUL might double the drainage rate on Toriel, making her age twice as fast. However, if a Boss Monster hybrid drains whoever registers as its parents, regardless of breed, Sans’ “SOUL power” might flow to it as well.

Assuming it’s like human pregnancy, Boss Monsters’ bodies might be adapted to withstand the draining of SOUL power. (whether by controlling drainage rate or just by having a lot of SOUL power to start with) If skeletons don’t reproduce the same way, though, Sans’ body would have no adaptations to the drain of SOUL power. If he is “the weakest enemy” (e.g., has a weak constitution and presumed low SOUL power) and the child’s draining is particularly aggressive, Sans might be rapidly drained and die.

Sans’ body probably couldn’t counteract this. Again assuming pregnancy parallels, his child’s skeleton genes probably couldn’t counteract it either. Ligers are so big because they have a lion for a father but a tiger for a mother. The lion father's genes encourage embryo growth, while tigresses (unlike lionesses) have no means of suppressing embryo growth. Indeed, it’s possible the child might inherit all the aggressive draining genes but no “whoa there, that would kill your parent” suppressing genes.

Why Sans Would be a Good Father

That title was somewhat misleading: there's no evidence Sans would be an especially responsible or attentive father. But he might be great for siring hybrid children. Again assuming soul power draining is like an embryo drawing nutrients from its mother, it might be good that Sans is the father.

In mammals, the father's genes build the embryo's side of the placenta, an organ the embryo uses to get nutrients. The father's genes encourage the placenta to draw in as many nutrients as possible; the mother's genes (in her body) act to weaken it.

If the child itself causes the flow of soul power, and the power-draining trait is influenced by imprinting like the placenta, then a hypothetical Boss Monster/skeleton hybrid with a skeleton father might have weaker soul power draining. Theoretically, Toriel, or the pair overall, wouldn’t experience the same strain as Asgore and a hypothetical female skeleton would.

Methods

Only two methods the author has considered would likely succeed.

Much of this article shall focus on the first method, which was inspired by Flowey. Loosely speaking, Flowey is a “hybrid” between the Boss Monster Asriel and a golden flower. By taking up Asriel’s dust, the golden flower eventually showed monster traits, such as being able to see, move, talk and create magical bullets. Monster dust/essence (or perhaps the injected Determination) also gave Flowey the ability to shapeshift to look like Asriel.

However, copying this method precisely (if with a human or human embryo this time) wouldn’t make a hybrid child, but a consciousness transfer. Thus, the method will have to be changed.

(This article assumes both "humans cannot use magic" and "humanity's seven greatest magicians, who made the barrier, were also humans" are both true. This work assumes they're both true by defining the magicians as not pure humans, but humans with monster SOULs. Thus, having a human SOUL wouldn't prevent magic use under the right circumstances.)

Dust Sample

Monsters turn to dust when they die. It’s unclear whether all their components become dust, or whether dust is the only thing that doesn’t simply evaporate upon death. In some works1, though, dust is explicitly a natural part of monsters’ bodies, and oozes out of their bodies when injured, like blood. Flowey has no SOUL; the flower that became Flowey absorbed Asriel’s essence via his dust. Evidently, it is Asriel’s essence/dust that allows Flowey to use magic; a SOUL is unnecessary.

Injecting a human embryo with blood-dust from one monster parent/donor might mean the eventual child could use magic, like Flowey. However, it wouldn't necessarily be the same type as the parent/donor: after all, Flowey attacks using little seed-bullets, not fireballs.

Magic Sample

Presumably, monster embryos/the equivalent of that grow surrounded by their parents’ magic. Injecting a magic sample from a monster parent/donor might allow a more monster-like development of magical abilities, and allow transfer of a particular kind of magical bullet.

In some works, monsters “bleed” magic, along with or instead of dust. If magic emissions (e.g., a bullet) will not do for providing a sample, bled magic might.

Determination Injection

Flowey only “woke up” as a flower some time after being injected with Determination. It is possible determination is necessary to allow monster essence/dust to give monster-like abilities to its vessel. It is unclear, because Alphys didn’t even know the flower absorbed Asriel's dust and apparently only tested determination injections on one flower.

The process is probably safe, at least in the short term. In the True Lab entries, Alphys took determination from (dead, collected) human SOULs; evidently the SOULs aren’t damaged very much by this process.2

The embryo would probably not turn into an amalgamate: the amalgamates' bodies were made from/mostly from magic. Alphys figures they merged together from a lack of physical matter; humans have plenty of that and are surely able to handle high determination levels anyway.

Variant: With a SOUL Chunk

Some works suppose monsters reproduce by tearing out or shedding chunks of their SOULs, which then merge. If a human soul can absorb a monster soul, it is likely a human SOUL can absorb a chunk of a monster soul, too.

When Flowey absorbed six human SOULs and the SOULs of nearly every monster in the Underground, he regained his original body back/looked like he did, and started the battle with fireball bullets like his parents'. It’s unclear whether he needed at least one monster SOUL to produce fireballs, or whether it was his own whims along with godlike power.

Just Make Flowey a God

If a monster absorbed seven human SOULs, the monster would gain godlike power. Creating a human-monster hybrid should be easy with that kind of power. It's the simplest method, but also the worst one: power corrupts and absolute power corrupts absolutely. This is also a frivolous use of such power, and if this secret were ever spilled to humans, the consequences would be dire. After all, humans attacked monsters out of the fear they would steal (and absorb) their SOULs.

Related Reading

Possible Health Problems of Hybrid Fanchildren

The Perils of a Boss Monster-Skeleton Hybrid

Kill la Kill: Geeps and Gut Microbes (contains very stylized and sparkly mild gore)

You Monster and Soul Dichromatism are examples. ↩︎

Bad Physical Effects

No human has a diet of pure energy. Therefore, the closest comparison is a diet of pure calories, with no other kinds of vitamins, minerals, or nutrients.

It’s unclear how long Chara lived with the Dreemurrs, but even a month is plenty of time for malnourishment symptoms to show up. Without the raw materials for growth, maintenance, and repair, Chara’s growth and healing would slow down or stop. Kwashiorkor, which comes from a lack of protein in the diet, is likely. So are vitamin deficiencies, with deficiencies of thiamine, folate, riboflavin, Vitamin B12, Vitamin A, and D2 being some of the most likely.

Bad Mental Effects

Several things cause hunger and satiety (fullness) sensations, such as the brain detecting low nutrient levels in the blood. An empty stomach, too, causes hunger: when empty, it sends signals and hormones to the brain that cause hunger. Conversely, if the stomach is full, it sends signals and hormones which lead to “fullness”. Similarly, if the guts are empty, they send signals that cause hunger pangs.

Monster food messes up the whole process, so even if Chara gets sufficient calories/the equivalent of calories, Chara may still feel hungry. After all, patients on nasogastric (nose-to-stomach) and parenteral (i.e., IV drip) nutrition, which also bypass the usual digestive route, can report hunger or even intense hunger pains even if they have enough nutrients.

Yet monster food has one big difference over these methods. Though monster food converts perfectly into energy when eaten, at least it’s eaten. It has a smell, flavor, and logically other aspects of normal food, and can be eaten socially. Hunger is partly psychological; even if nothing gets to the stomach or gut, the act of eating and receiving energy may stave off hunger for a while.

One bigger problem, beyond whether the human body can handle a diet of pure energy, is whether the human brain can. Other organs can work on multiple fuels, but the primary fuel of the brain is glucose. A shortage of glucose to the brain (neuroglycopenia) can cause disturbing symptoms, including impaired judgement, irritability and even personality change.

Conclusion

Assuming monster food of Chara’s time converts perfectly to pure energy in humans as well as monsters, and monster food isn’t enriched with any vitamins or minerals, Chara would have died even without the buttercup plan.3 If a diet of almost entirely sugar is a valid comparison, on a pure monster-food diet Chara would die within two months.

So does that mean Chara must have had physical food? Not necessarily. Neither Dreemurr home has a toilet or even an outhouse4, suggesting physical food wasn't common enough to merit it, at least at the time.

Yet, it would be easy for Chara to acquire some physical food: the Underground has a lot of Typha plants. Several Typha parts are edible raw, so Chara could eat some parts without needing help to cook it.

A diet of "pure energy" would probably register as constant energy from chemical bond-breaking. That, or something like electricity, for some bacteria can “eat” and “breathe” pure electricity. The oriental hornet, which is closer to a human, also gets a small part of its energy from the electricity from a natural solar panel on its abdomen. ↩︎

Vitamin D has a special risk here, since a major route of Vitamin D production is sunlight (specifically UVB wavelengths) on skin triggering Vitamin D synthesis. ↩︎

Notably, the symptoms of some vitamin deficiencies are susceptibility to infection and fatigue. Some symptoms (e.g., hypersalivation from niacin deficiency) even mimic buttercup poisoning specifically. Post-mortem, monsters could plausibly believe Chara’s cause of death was food-related. ↩︎

This candidate doesn’t match all the requirements of the above definition, but it does meet most of them. That all encounter-able monsters1 emit bullets at Frisk might mean it’s irresistible. All encountered monsters use magic, so, obviously, it must have occurred at some point in development. If one defines monsterkind as a single “species”2, it probably occurs in every member of the species.3

For a), b), and d), the fact Papyrus’s bullet patterns changes to a particular one when he’s thinking about Sans may count as proving the point. It may also count as an example of f), for, although magical self-expression can clearly be controlled, this bullet pattern behavior seems involuntary of subconsciously controlled.

f) and g) are trickiest to match up; there’s no information on whether monsters automatically become able to use magic on maturation (like birds “learning” how to fly) or must be given formal instruction. It’s known Asgore taught Undyne how to fight, and Undyne in turn gives Papyrus combat lessons. Yet, this might not be teaching on use of magic in itself, but how to use magic in a combat scenario. (Learning how to walk is more or less instinctive; modifying that behavior into a military march isn’t.)

If one goes by the alternate Wikipedia definition, though, this is much easier to answer:

“Instinct or innate behavior is the inherent inclination of a living organism towards a particular complex behavior”.

Monsters do seem inherently inclined to emit magical bullets. Often, people are inherently inclined to do things that are pleasurable, such as eating tasty food.

A book in Snowdin’s library suggests self-expression via magical bullet patterns makes monsters happy, and often animals are happiest when they can engage in instinctive, natural behaviors, such as searching for food.4 Emission of magical bullets is certainly a “particular complex behavior”: monsters have multiple bullet patterns, sometimes an individual pattern is complex, and these patterns can be mixed together in battle.

Do Humans Have Instincts?

In a way, monsters’ bullet patterns parallel language, and it’s often argued people pick up a language instinctively. After all, babies acquire a language from surrounding people with no special teaching. A hearing baby raised by deaf parents will even “babble” in sign language. Emotional self-expression, in humans, seems instinctive: even blind babies who have never seen a smile do so.

Humans’ behavior is very malleable; they have few outright instincts. For humans, most of their instincts relate to their social nature. They naturally* cooperate, follow gazes, read emotions, and mimic body languages (if subconsciously), though to what extent they do these things varies simply because human behavior is so variable.

Human and Monster Instinct Overlap

Monsters’ society is very similar to human societies, through traits such as building homes, liking artwork, wearing clothes, having jobs, reading, using tools, and a symbolic economy (“G” is presumably gold coins). (Admittedly, not every human society does all these things, but they all do several of those.) This surely means their psychology is broadly like a human one, and surely packed with similar social instincts.

Incidentally, monsters might mimic human behavior even if the original context or purpose of those instincts are different. For example, Boss Monsters look something between a goat and a lion, so in some works their behaviors are similar to goats, lions, or a mixture of the two. If Asriel, due to goatlike/lionlike instincts, seeks out physical proximity with Chara, Chara probably wouldn’t think anything strange of it, because some humans also enjoy physical proximity with others: it’s a reasonable byproduct of being a social species.

In conclusion, monsters probably do have instincts, but for the most part their instincts seem to be the same as (or equivalent to) human instincts, so it’s no big deal.

--

Except Monster Kid. Monster Kid is very scared at this point, though, so it could be argued Monster Kid is paralyzed with fear. Potentially, one instinct could be interfering with another. ↩︎

Interpreting Gerson’s use of the word “breed” literally to suggest individual monster types are like dog breeds, not distinct species. ↩︎

So Sorry seems to depend on a magical pencil for magical self-expression. Alphys indisputably emits her own bullet patterns only once, and briefly. In the Lost SOUL battle, she uses Mettaton's attacks. It makes me wonder whether monsters can be born with or acquire problems that interfere with magical self-expression; dogs might naturally chase small animals but a dog born with limb deformities would have trouble chasing anything. ↩︎

3. Relation Between Them

Though the idea HP equals hope and fallen down monsters have no hope is just speculation, if it's anything like give-up-itis, it makes sense. People with give-up-itis are hopeless: they are swallowed up in despair and helplessness. Those in the later stages are practically comatose: they lie down and become unresponsive, like monsters in the fallen down state apparently are. (see True Lab Entry #6) After a while in these states1, they die.

Incidentally, monsters' status is something like prisoners of war. Humans sealed monsters underground after winning the war, and though the Underground seems big (some parts are inaccessible), it's far smaller than the Surface. Even monsters who never fought in the war live and die without ever seeing sunlight, and over the course of their lives they may think of the Underground as a prison.

4. What is Determination?

So why does Determination (customarily capitalized when referring to the substance) cure the fallen down state?

Though it's unclear how give-up-itis kills people, the symptoms parallel impairment in a certain brain circuit and “voodoo death”. The latter has multiple possible explanations, but generally it happens when people think they can’t escape a terrifying fate (e.g., a deadly curse). Sheer terror overloads the body with stress hormones, making it collapse, like an evil version of a placebo effect.

A Snowdin library book says monsters are “attuned to their SOULs”. It's possible monsters’ SOULs are equivalent to human brains, in that they control some body functions. Therefore, the sheer lack of hope may lead to lowered body and mental health, like in voodoo death.

Determination (the power, not the substance) is defined as: “The will to keep living... The resolve to change fate.” Those who persist, who endure, in the face of the hopelessness of being a prisoner of war could reasonably be called “determined.” It's possible injecting Determination into monsters' bodies works like a sort of cross-species neurochemical transplant. The state of “fallen down” is reversed, like how the drug L-dopa (temporarily) awoke people from comas.2

It's unknown how Undyne has Determination; some speculate she produces small amounts naturally. If so, perhaps monsters can withstand small amounts of Determination, and the Amalgamates happened only because Alphys injected far too much. If Determination injection is anything like cross-species blood injections and transplants, of course serious effects would happen.

It's unclear how long the fallen down state lasts, though Mettaton's diary suggests it can last a while. ↩︎