Assume we are dealing with a society similarly advanced to our own but thanks to finding some data-stores of advanced technology are far more capable at genetic engineering.

With that extra genetic engineering knowledge they have made various demi-human races: cat-human, bird/flying-human, amphibious human etc. These demi-humans fill various roles in society but are treated fairly poorly, as lower caste/disposable slaves.

There are also various subspecies of each of the demi-humans which are denoted by their different features. For example among the cat-human their are different fur & hair length/colour, ear size & shape, nocturnal nature, carnivore/omnivore etc.

The Questions

Assume that cross breeding is possible and that we can also ignore unusual/useless cross breeds (aquatic human with wings).

How realistic is it for the results of crossbreeding to have a mix of complete features from both species? For example, the cat/bird/human has wings, a cat's tail and human eyes.

How likely are genetic accidents? For example, the cat/bird/human has half formed non-functional wings, a vestigial tail and mismatched eyes.

Keep in mind for these questions that this society has access to advanced genetic engineering. They could attempt to make it so crossbreeding will function as successfully as possible. However, the vast majority of these crossbreeds are slaves/low caste members and could not afford expensive treatments for every child.

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    $\begingroup$ You are asking a lot of different questions at once. Can you edit this ask one specific question. $\endgroup$ – sphennings Jan 5 '18 at 0:04
  • $\begingroup$ Changed one of the questions to an assumption to try and focus more on the feature crossbreading part of the question. $\endgroup$ – Typhado Jan 5 '18 at 0:17
  • $\begingroup$ You may want to look into transhumanism. $\endgroup$ – The Square-Cube Law Jan 5 '18 at 0:19
  • $\begingroup$ If you intend for this to be science-based (speculatively), you should include the science-based or reality-check tags. Otherwise, how this magic genetic engineering works out is entirely up to you. $\endgroup$ – jdunlop Jan 5 '18 at 0:53
  • $\begingroup$ I would rather suspect that in a world where such advanced genetic engineering is available all babies are designed so that they have whatever phenotypic characteristics their parents or masters want and screened to eliminate malformations. It is implausible to assume at the same time widespread availability of quasi-magical genetic engineering and birth defects. $\endgroup$ – AlexP Jan 5 '18 at 1:07

This is a good idea for a story.

I like the idea of "plug and play" genetic engineering - genetic modules which can be easily added to a oocyte (also purchased from various stock lines) which is then induced to develop into a fetus. The demihumans are grown as needed or desired by the overlords. Genetic modules corresponding to various demihuman attributes are produced and advertised by various competing companies, domestic and foreign.

First generation demihumans are each custom jobs started from scratch and the plug and play modules generally perform as advertised. An enthusiastic overlord might get his new demihuman into trouble by mixing modules from different vendors or perhaps attempting too many modules on one individual.

Not that this is not dark enough, but you could then take a page from current agriculture practices. For millennia farmers saved seed to grow next years crop from this years. With the advent of hybrid crops in the 1930s, farmers had to buy new seeds each year because the hybrids would not breed true and one would get inferior F1 crosses. This is true too for genetically engineered seeds. The module companies do not want you to breed your own winged humans because where is the profit for them in that? You need to buy modules and make each winged human from scratch. By design the modules will not breed true and so your plug and play custom demihumans will not breed true if allowed to breed willy nilly with each other.

But of course there will be places where they do congregate among themselves. There will be ghettos of tragic freaks and misfits as you suppose. There will also be the possibility of the unexpected - pieces of different genetic modules recombining with meiosis, jumping to a new part of the chromosome - making something new. Maybe something better.

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If the demi-human is too different from a human (flying human for example) it will probably not be able to interbreed with humans. If it only has minor modifications they will be able to crossbreed.

This concept is measured by genetic distance.

A demi-human with very minor modifications (maybe he has fur instead of skin) might be able to interbreed with a normal human. But in that case the offspring wouldn't look too strange. In that specific example the offspring would probably be a very hairy human. That s because the genetic distance is very small.

A demi-human that can fly will probably have a genetic distance vastly superior than homo sapiens has with chimpanzees. That s because you need to modify A LOT of genes to make a flying Hominidae. You can forget about interbreeding.

To summarize:

If the genetic distance is too big you just can't interbreed, those flying demi-humans are not really humans anymore. They have less in common with us than chimpanzees have with us.

If the genetic distance is close enough you can have offsprings like tiger and lions =>ligers but they will be sterile and interbreeding might not always work.

If it s very close then yeah you can interbreed but the offspring will be a boring normal human with some minor unusual features.

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