It is not explicit, but it is very likely that exist. The fact that a human and an elf generate a half-elf makes me belive that genetics is real in D&D.
It's interesting how two people can have the same data, and come to completely different conclusions. While it's true that in D&D some mechanism of heritable traits seems to exist, it's almost certain that it is not DNA and the half-elf is a fairly good example of that. As different as elves and humans are in D&D, that they can breed at all suggests that its not something as specific as chromosomes that underlies heredity. More over, not only can they interbreed, but they don't form sterile hybrids like mules. Half-Dragons, Half-Fey, and other more unlikely hybrids are even stronger examples. This implies a more pliant, magical, and perhaps spiritual means of heredity.
It's a good practice to assume that the science in the average D&D world works very like the science in its source material. For example, the myth of the Minotaur gives a good understanding of how heredity is assumed to work in fantasy, and which we must assume is in force within a fantasy RPG. DNA would never allow bovine traits to be inherited by offspring. In fantasy, the mythical minotaur's parentage and the resulting monstrous nature of the offspring makes perfect sense.
I did not expect that someone would find my mechanics complicated.
It's not that they are complicated that bothers me. What bothers be is that they are a distinctive subsystem that much of the time seems to have no relation to any other rules of the game.
But consider that the intention was to be realistic.
Realism is no guide in a world where a dragon can mate successfully with a half-elf. The answers can't be found from reality; they are whatever you want it to be within the setting.
In fact i already had a more complete content about it, however i was not sure about my knowledge. I decided to make a simplefied verson, and latter make a full version. I am studying about it. I hope in a few days i already bid more details about the baby health.
Cool.
Could you elaborate more about it?
I mean I'm imaging myself as a DM in a campaign where one of the PC's is pregnant, and all the consequences that might result from that. For the most part, I'm not worried about the baby being wounded, as I figure most anything that kills a kid while on board will also kill the mother. Indeed, typically it's easier to kill the mother than the kid from things like falls and blows and the like. So for the moment, let's not worry about where a sword thrust hits a mother and how deeply. Called shots like that go against the spirit of D&D anyway.
What I am worried about is things like...
...whether magic plate mail fits on a woman that is 6 months pregnant.
...does the weight of a pregnancy count against encumbrance. How much does a pregnancy weigh?
...if the mother is the target of a Poison spell, is the child effected as a well?
...if the mother casts Death Ward on herself, is the child protected as well?
...Does the infant count as a separate creature if within the radius of a Circle of Death?
...If the mother is polymorphed, does the infant change into a fetus of the same type as the mother, and is this dangerous in any way?
...Does an unborn infant have an intelligence score of at least 1? (Presumably, yes.) If so, can I detect one with the spell Detect Thoughts?
...Does taking nonlethal damage from a source like starvation, thirst, or heat exhaustion effect the health of the infant? If so, how and how much?
...When an infant is born, what percentage of its adult stats does it have? (I have already ruled on this in my game, but I'm noting I had to rule on this and you haven't.)
...How are the adult stats of an infant determined?
...How old does a child need to be before it can gain XP?
...Can a Night Hag send a Nightmare to an unborn infant? Can a mother detect this? Can an unborn infant be possessed by Mind Jar? In general, how does the mother's Will/Will save protect the infant, if at all?
The idea of this book was about pure biology, however i think to add more role play elements, such how the races react towards the act of birth.
What do you suggest to make this book more interesting?
I think you should focus on crunch. Fluff is likely to be specific to a particular DM's campaign world, but good crunch is something most DMs can use.