The Half-Races

There are numerous Half-creature races in Faerûn. Their nature is fairly deterministic based on their parentage. Exceptions exist, usually the result of the influence of magic. In general this is a guide for Half-Elf characters, Half-Orc characters, and to explore the lineage of the Plane-touched races (Aasimar and Tiefling) and even more exotic combinations (such as the Half-Dragon).
To start, it is important to recognize that Human blood is almost always capable of comingling. The reason is lost to the mystery of time, but it is true that the human essence is the most flexible. It is also the least dominant. In theory, any creature that is part human can procreate with any other creature that is part human. Humans can (and frequently do) directly procreate with Dragons, Celestials, Abyssals, Orcs, and Elves (and very rarely Dwarves). Orcs are not as compatible as Humans, but can couple with almost any other type of Goblinoid, Humans and Dwarves.
Humans and Dragons : Offspring is Half-Dragon as is their future progeny. A Half-Dragon that mates with any other Half-Race produces another Half-Dragon, until, it doesn't. After that time no children are born Half-Dragon, but a trace of draconic essence remains (many Sorcerers make this exact claim, and some of those are real).
Humans and Celestials/Abyssals (Plane-touched) : These unions produce Aasimar (if one parent is Celestial) or Tieflings* (if Abyssal). Aasimar and Tieflings breed true. Rarely a coupling of a Tiefling and an Aasimar together produces a Human, and those that have been born have always ascended to positions of incredible power and influence. When Aasimar or Tieflings mate with other Half-creatures, the children exclusively follow their Plane-touched parent, the blood is so strong.
Orcs and other creatures : A Half-Orc can have any mix of Human, Orc, Hobgoblin, Dwarf or even Gnoll in them. They are simply called Half-Orcs. Orc blood overrides Dwarf, Elf and Human blood after a time. Within two generations or so, descendants trend back toward just Orc. The savage Orcs will sometimes procreate directly with Dwarves who have been taken and the result is pure Orc. Orcs can never produce offspring with Elves directly, but it is possible that a Half-Orc and Half-Elf might (their offspring would be Half-Orc).
Dwarves and other creatures : An almost invisible group are Half-Dwarves, who are so similar to their Dwarf parentage as to be indistinguishable from normal Dwarves. Half-Dwarves may be the offspring of a Human/Dwarf, Gnome/Dwarf or even a Halfling/Dwarf. Non-dwarven mates who enter into dwarven culture are honored and respected by dwarves for their bravery and loyalty. Half-dwarf races were common in Ardeep, Eaerlann, and Myth Drannor at one point in history but by 1350 DR or so they were largely unheard of.
Humans and Elves : The first union produces Half-Elf children, and after that, if any other Half-creatures are included in the mix, the elvish blood always recedes. A rare Half-Elf / Aasimar pairing will produce Aasimar children (presumably the same would be true with Tieflings, though no such offspring are known). Within the elvish, Wood/Wild Elf blood is strongest, with Silver blood overcoming Gold, and all of them are more potent than Drow. When Drow pair with any other type of elf, the result is never Drow. Only Humans and Drow produce Half-Drow, and the children of a Half-Drow will never be Drow unless the other parent is pure.

* rarely (and usually with the interference of obscene magic)

unions between a Human (or Tiefling) woman and a Demonic

male produce a Cambion as offspring; more cunning, cruel and

deadly than Tieflings but still able to gallivant on the material

planes as mortals do.

---

Essence Hierarchy for Half-creatures:

Dragon

Plane-touched (Aasimar, Tiefling)

Orc

Dwarf

Elf (Wild / Silver / Gold / Drow)

Human

The following races do not seem to be able to mix across species (except with Dwarves) but it is not known why.

Gnome

Halfling

Dragonborn (Half-Dragons are NOT Dragonborn)

- - -