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INTER-SPECIES FERTILITY

Amongst races, there are four varying breeding relationships listed in Table A.

Table A: Relationships
Relationship Example
Identical human vs. human
Similar human vs. elf, human vs. halfling
Related human/horse vs. centaur, human/elf vs. half-elf
Different human vs. eagle, human vs. horse

TABLE A: Relationships

Relationship   Example
Identical      human vs. human
Similar        human vs. elf, human vs. halfling
Related        human/horse vs. centaur, human/elf vs. half-elf
Different      human vs. eagle, human vs. horse

Whether or not two individuals can produce offspring depends on the relationship and conditions given in Table B.

Table B: Relationships Based on Conditions
Relationship: Identical
Additional Requir.: None
Chance of Fertility: As normal
Result: As per race
   
Relationship: Similiar
Additional Requir.: None
Chance of Fertility: As the lesser fertile of the two races
Result: Half Breed
   
Relationship: Realted
Additional Requir.: None
Chance of Fertility: As the lesser fertile of the two races
Result: Produce pure breed of the race the size of the female (see below)
   
Relationship: Different
Additional Requir.: Magical or divine intervention
Chance of Fertility: 0% (without intervention) or 100% (with)
Result: Produce a new race that may be fertile and breed true

TABLE B: Relationships Based on Conditions

Relationship:        Identical
Additional Requir.:  None
Chance of Fertility: As normal
Result:              As per race

Relationship: Similar
Additional Requir.: None
Chance of Fertility: As the lesser fertile of the two races
Result: Half breed

Relationship: Related
Additional Requir.: None
Chance of Fertility: As the lesser fertile of the two races
Result: Produce pure breed of the race the size of the female (see
        below)

Relationship: Different
Additional Requir.: Magical or divine intervention
Chance of Fertility: 0% (without intervention) or 100% (with)
Result: Produce a new race that may be fertile and breed true

Size (of the creature you filthy minded churl) may play a part in some crossbreeds. For example, in human/horse/centaur pairings. The result depends, in part, on the physical size of the parents. Consult Table C.

Table C: Size
Realtionship Race of Father> Race of Mother Race of child
Similar Human (Elf> Elf (Human) Half-elf
Related Human (Half-elf) Half-elf (Human) Human or Half-elf
Realted Elf (Half-elf) Half-elf (Elf) Elf or Half-elf
Different Human Horse Centaur (with interv.)
Different Horse Human None (or a dead woman)
Related Human (Centaur) Centaur (Human) Human
Realted Horse (Centaur) Centaur (Horse) Horse

TABLE C: Size

Relationship   Race of Father   Race of Mother   Race of child
Similar        Human (Elf)      Elf (Human)      Half-elf
Related        Human (Half-elf) Half-elf (Human) Human or Half-elf
Related        Elf (Half-elf)   Half-elf (Elf)   Elf or Half-elf
Different      Human            Horse            Centaur (with interv.)
Different      Horse            Human            None (or a dead woman)
Related        Human (Centaur)  Centaur (Human)  Human
Related        Horse (Centaur)  Centaur (Horse)  Horse

There is one interesting exception, humans and halflings. While they are fertile with each other, such a pairing will only produce one or the other race. This may be because they are so similar that there can be no half breed race. Consult Table Cb.

Table Cb: Halfling-Human Size
Relationship Race of Father Race of Mother Race of Child
Similar Human Halfling Halfling
Similar Halfling Human Halfling or Human

TABLE Cb: Halfling-Human Size

Relationship   Race of Father   Race of Mother   Race of Child
Similar        Human            Halfling         Halfling
Similar        Halfling         Human            Halfling or Human

For some specific races, the relationships are given on Table D.

Table D: Specific Races
Race Relationship Examples
Centaur Similar None
  Related Horse, Human
  Different Most other races
     
Elf Similar Elf (all varieties)
  Related Drider
  Different Most other races
     
Half-elf Similar None
  Related Elf, Human
  Different Most other races
     
Centaur Similar Elf, Halfling, Ogre, Orc (and variations)
  Related Centaur, Half-elf, Half-orc, Minotaur, Satyr
  Different Most other races

TABLE D: Specific Races

Race      Relationship    Examples
Centaur   Similar         None
          Related         Horse, Human.
          Different       Most other races
Elf       Identical       Elf (all varieties)
          Similar         Human
          Related         Drider
          Different       Most other races
Half-elf  Similar         None
          Related         Elf, Human
          Different       Most other races
Human     Similar         Elf, Halfling, Ogre, Orc (and variations)
          Related         Centaur, Half-elf, Half-orc, Minotaur, Satyr
          Different       Most other races

On the specific case of and elf and a centaur use the following suggested rules:

These rules are not complete but hopefully gives the GM a good base to develop specific rules for inter-species breeding.