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I asked a similar question 2 years ago and never got a real answer. I was told the question was too broad or "it can be whatever you want" "magic can do anything" so I thought I'd tighten it up a bit. As a bit of background, my world will be filled with hybrid animals who got their DNA shuffled by volatile magic. Obviously not everything will survive, that's kind of the point, it was disastrous, like the biblical great flood. Lots of things died instantly, turned into abominations that didn't live more than a few days or hours, and things that lived and survived and reproduced. I live playing with speculative zoology but I don't know enough about it to say for certain a hybrid would realistically survive. All of the hybrids I have now are custom-tailored to ecosystems, which I love doing. However...


I'd like to know if there was a way to really test if a hybrid would survive. Like a list of rules or guidelines to follow. There has to be something like that even in our world. Like for example a hummingbird and a bat of some sort, what would it need to have to survive? I'm not asking anyone to world build for me, I'd just like to know if there are any resources I could use to better understand the rules of species survival.

What I Am Asking For

  1. Any resources to help understand the rules of survival/adaptations
  2. A checklist I could use to determine if a Hybrid Animal would survive
  3. Any useful advice when making fantasy animals
  • $\begingroup$ Like for example a hummingbird and a bat of some sort, what would it need to have to survive? A bird and a mammal, eh? Two branches a bit too far away on the evolution tree. I'd like to know if there was a way to really test if a hybrid would survive. I reckon you should start with the basics of the sexual reproduction, specifically meiosis. Add a sprinkle of aneuploidy $\endgroup$ May 20, 2020 at 1:42
  • $\begingroup$ @AdrianColomitchi I'm not particularly worried about reproduction right now, more the adaptation side of things. for example, if a lion had hooves it wouldn't be able to catch prey well and would die. $\endgroup$ May 20, 2020 at 2:11
  • $\begingroup$ The platypus - no rules no restrictions evolution. $\endgroup$ May 20, 2020 at 2:20
  • $\begingroup$ Why is everyone so mean to the poor platypus? If it wasn't adapted to it's environment, it would be dead and we wouldn't be talking about it. $\endgroup$
    – DWKraus
    May 20, 2020 at 4:40
  • $\begingroup$ Are all organisms included (like bacteria and plants)? How does the hybridizing work? Does it just combine any organisms that happen to be near each other? $\endgroup$ May 26, 2020 at 6:29

3 Answers 3


The only true law is what makes more critters going forward. Unfortunately, the best way to determine if something should work without a genetics lab and/or a few thousand (million?) years is to use intuition and a lot of thinking. A good general knowledge of how animals do all the things they need to do needs to be combined with a gut instinct about what could work and what could go wrong. in the long term, lots of things CAN work, but even small differences can make a huge difference about what works best. There are some things all animals need to do, and if your organism can do them, it's at least viable (although not necessarily successful). If all your organisms start out weird, there is some time for evolution as even A lion with herbivore teeth can gnaw at a deer and eventually eat it if it can use the energy and kill the prey. The issue with evolution is that your animals will gradually start looking like the animals that used to exist. Fanged deer will either become swift eaters of small prey and grow to resemble predators or they will lose fangs as they try to eat grass with bad teeth. Evolution isn't intelligent. Any trait that doesn't give an organism an advantage will mutate and be lost or become non-functional. Any trait you want your organisms to have must confer some real advantage to be kept. Lions with horns need to be impaling prey with them or using them for mating rituals or digging with them for giganto-mice or using them as periscopes to breathe.

  1. Eat - Choose what the organism can eat, then give them the mechanical and biochemical ability to eat it. Teeth to chew, stomach/intestines that can digest. This includes catching prey or seeking plants. Fangs, claws, spikes and what-not to catch (if predators) or grinding surfaces, foraging tools (like a digger) and long necks for herbivores.This also includes excretion of waste and processing environmental toxins
  2. Breathe - gas exchange is critical and can heavily influence how and organism functions. Fish with lungs will need to come to the surface regularly like whales or else adapt to the land like early amphibians. Gills immediately force an aquatic lifestyle. Insects are small because of how their gas exchange system works.
  3. reproduce - this is one of the biggest drivers of adaptation, and the reason most of your species that survive initially will die out. Reproduction is a thousand subtle things from matching numbers of chromosomes with identical genes to attractive displays keyed to specific members of the opposite sex, to matching genitalia. within a species, these shift slowly and must be closely paired. You will need some serious hand waving or justifications to compensate for this (like the various hybrids in the Xanth series of books)
  4. Don't get eaten - This is important, but not as much as you might think. Lots of species in protected niche environments have found themselves with no/few predators and evolved into things that can't deal with predators. But where there are predators, you have to not get eaten (at least until you reproduce). But everything dies, and if you reproduce first your death is not nearly so critical.
  • $\begingroup$ So if the male parts don't fit with the female parts.... Probably a universal rule. $\endgroup$ May 26, 2020 at 12:36

The long and the short of it, is that there are perhaps no rules, except possibly one. Think platypus. It has no legitimate reason why it should exist, but it does. Nature is filled with other examples.

Fish that can walk on land.

Frogs that can live under water.

Squirrels that can fly.

Dinosaurs with fathers.

Insects with eyes on their bellies.

Mutant lizards with two heads.

Animals with gills (google it).

Birds with four legs (bats).

Tadpoles that turn into frogs (hybrids during the transformation).

Caterpillars that turn into butterflies.

Kangaroos with a pouch.

Beaks with teeth (hummingbirds).

Whales with a ruminant digestive system.

Fish with no stomach.

Hairless cats and dogs.

Pigs with fur.

Males without a Y chromosome.

Female animals that do not carry the fetus, and males that do.

The list goes on and on.

Every time you think you have found a rule, you can probably find an animal on earth that breaks it.

There is one rule I did not find an exception to, but it seems possible. That is hooves and hands with paws on the same animal, but I can not think of any good reason why one shouldn't exist. It would take a complicated genome, with separate genes for hands and foot, but kangaroos have very different front limbs from back limbs, humans have very distinct hands and feet, and birds have very different front legs (wings) than back legs, so obviously it is possible.

However, one rule that seems to be almost inviolate and universal is lateral external symmetry. That is, the left side looks like the right side (or a mirror image) on the outside, with only minor variations. What is on the left, is on the right. Still, there were Trilobozoa, animals with three symmetrical sides, so could it be possible? An animal with fins on one side and legs on the other? Perhaps not, it would be easy pickings, methinks. Balance and locomotion would be extremely difficult, so I can not envision it would have survivability. Even fish are bilaterally symmetrical. But could it be a genetic one-off exception? There are very good examples of humans and animals with deformed limbs and genetic limb abnormalities through birth defects that have survived and lived long and prosperous lives.

  • $\begingroup$ Insects with eyes on their bellies? Explain please. Female animals that do not carry the fetus and males that do? If you are talking about seahorses, that's a myth. $\endgroup$ May 26, 2020 at 6:32
  • $\begingroup$ @Praearcturus Can't find the reference, but they are called ocelli. It was hypothesized that they were in the belly to stabilize flight. en.wikipedia.org/wiki/… See en.wikipedia.org/wiki/Male_pregnancy for male pregnancy $\endgroup$ May 26, 2020 at 12:33
  • $\begingroup$ Here is the refrence "Genital photoreceptors have been identified in many adult butterflies, developing during the pupal stage. These receptors provide little in the way of resolution and are thought to be involved in oviposition behavior, informing the female that the ovipositor is extended far enough to successfully lay eggs. They also play a role in copulation in the male, providing information that the vagina of the female is aligned properly for penile insertion." sciencedirect.com/topics/agricultural-and-biological-sciences/… $\endgroup$ May 26, 2020 at 12:47
  • $\begingroup$ Male seahorses simply carry the eggs that the female laid. That thing about genital photoreceptors is interesting though. $\endgroup$ May 26, 2020 at 15:27

Consider the DNA to be an instruction manual for building a creature.

Imagine you have an instruction manual for building a snowblower from scratch. It is thick - you have to find the raw materials or make what you cannot find and then assemble the thing. The manual also includes instructions for proper use, maintenance and repair. It is a weighty tome, this manual, but not a bizarre thing.

Now another manual, this to build a kitchen food processor from scratch as well as proper use, maintenance and repair.

This is how the DNA for a creature is.

Now you will hybridize the food processor and the snow blower by mixing their manuals up. Both manuals are in Kazakh, which helps (and the language for genes is DNA code), and they are divided into chapters (chromosomes) and your mixing of manuals sticks to chapter by chapter insofar as you are able.

The problem is that crucial steps from the snowblower assembly will be lost, and replaced with steps from the food processor that are not analogous. Or are duplicative. Thinking about it this way, it is easy to see that if instructions on the snowblower internal combustion engine are replaced with something else, the thing will not start or will blow up or quickly break.

Random mixing as occurs with sexual reproduction will be a disaster unless the plans are very similar as with 2 individuals of the same species. For example 2 food processors from the same company will have similar manuals and you might shuffle them successfully. You might hybridize a crow with a raven successfully. Plants have more flexibility and different species in the same genus and even family can hybridize; citrus is a good example. In real life as I understand it, chromosome number is the big issue preventing intraspecies hybridization. If the snowblower manual covers material in 3 chapters and the food processor takes 5 for the same material, the chapter count will get off in a hurry.

I think to work, animal hybridization must stick 95% to one body plan with only a small amount from the other. For example, if the only part of the food processor manual that entered the hybrid was "suggested uses" and the rests was from the snowblower manual, you could process some food with your snowblower. If the piece about the blade were the only substitution I could imagine a snowblower with food processor blades. I am thinking of plants in the legume family which have one animal gene - hemoglobin - that they acquired in the distant past and successfully use today.

This rule will not give you centaur / manticore / mermaid Piers Anthony Xanth style hybrids. I think it would be fun scifi only for true nerds who groove on things like leghemoglobin and like thinking of other ways a very limited gene import from a distant species might improve the fitness of the import recipient.

  • $\begingroup$ Platypus. "The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, and the first scientists to examine a preserved platypus body (in 1799)[4] judged it a fake, made of several animals sewn together.[5]" en.wikipedia.org/wiki/Platypus $\endgroup$ May 26, 2020 at 12:40

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