More Gygax’s Finches

In a previous Gygaxian naturalism post I gave some thoughts on D&D implications of allopatric speciation. This is what people usually have in mind with evolution, where two populations are physically separated and so diverge genetically, especially if the two environments differ. For instance, a storm blows finches from the mainland to an island which both has a different climate than the mainland and presents a barrier to gene flow.

A more unusual form of evolution is sympatric speciation and its companion of disruptive selection. Sympatric speciation occurs when there is divergence despite no geographic barrier to gene flow. Disruptive selection is when selection promotes extreme forms and weeds out intermediate forms. The two are connected since disruptive selection is one way sympatric speciation can work.

As with last time, let us consider the orc, but this time by contrasting them to goblins. Orcs and goblins are both nocturnal humanoids. They both live in dungeons. And WotC era D&D lore notwithstanding, we can assume they have a common ancestor. If orcs and goblins were to develop into different species via allopatric speciation, they’d have to be geographically separated but that doesn’t fit with them having the same geographical range (i.e., they appear on the same random encounter tables). So we need a sympatric speciation explanation and that means disruptive selection.

For disruptive selection to work, we need to see less survival and/or reproductive success for intermediate forms. So really this means big orcs and small goblins should survive and have lots of babies but medium goblin-orcs should die young and/or be last asked for a dance at the dungeon winter formal. Let’s suppose that for the goblin and orc population that fitness basically reduces down to martial prowess. The more dwarf and elf skulls males collect, the younger they marry and more extramarital pairings they attract. So why would you be a badass as a 4′ tall goblin or a 6′ tall orc but not as a 5′ tall intermediate form?

This comes down to different tactics. A 6′ tall orc will make great heavy infantry, fighting via brute strength. A 4′ tall goblin can serve either as a wolf jockey or as a hit and run tunnel ambush fighter. But a 5′ tall compromise between an orc and a goblin either ends up getting mauled by his own wolf, annoyed by a painfully oversized rider, or ditched by the heavy infantry unit, annoyed at the runt barely able to lift the sword. Over time this will lead to a bimodal distribution in size rather than the usual normal distribution and we will effectively have two species, or at least subspecies. Since humanoids aren’t just brutes but have culture, you may even see cultural norms and institutions develop that discourage cross-breeding between goblin women and orc men (or vice versa) as it is likely to result in pathetic 5′ tall goblin-orcs who will sire no grand-imps.

Once we have this logic, we can extend it to see why there would not only be a distinction between wolf-riding goblins and shock troop orcs but also trap-setting kobolds and hyena-whisperer gnolls. Or for that matter why the bestiary has an entry for a black pudding and another for a gelatinous cube but not one for a translucent aspic.