Randomly generating worlds can be complicated, and WorldGen can create lots of many different types, with a wide range of conditions. A small slice of those worlds support life, but ‘life’ covers a very wide range of possibilities across billions of years of evolution.
WorldGen splits life into a small number of very broad categories, which assume a relatively linear progression that follows the evolution of life on Earth. Real exo-planets may well be more complicated, but this simplification would probably work well enough for a game. The main purpose is to provide a wide range of interesting worlds to explore in an RPG, not to be completely scientifically accurate.
As part of the world definition, the types of things (resources, animals, plants) that are found on that world are listed, along with a (randomly generated) description of what they are like. The former will be used as part of the trade system, the latter is just flavour text.
The First Life
Worlds classed as Organic are generally lifeless, but they have large quantities of organic matter which is the building blocks of life. There may be small numbers of prokaryotes, which are the first simple life forms, but they haven’t spread or developed enough to be considered widespread.
On Earth, prokaryotes are a simple form of singled celled life which lacks things common to eucaryotic life – specifically a nucleus, but there are other differences as well. Prokaryotes are divided into bacteria and archaea, and long with eukaryotes (everything more complicated than prokaryotes, including us) make up the three domains of life on Earth.
But this brings us to a complication, in that how should exo-life be classified? It may be tempting to call things bacteria because they look and behave just like bacteria does on Earth, but biologists define life by their genetic differences. Exo-bacteria will probably be genetically nothing like Earth-bacteria, they may not even consist of DNA.
As life becomes more complicated, and we have cyanobacteria (blue-green algae), protozoa (single celled animals), metazoa, sponges, jellies the definitions we are used to on Earth become more dependent on that life form’s position in the genetic tree.
So is it correct to call a multicellular organism full of pores and channels which allows water to circulate through them a sponge? Or does it have to be of the phylum Porifera and descended genetically from ancestors on Earth? Scientists in our fictional settings probably have a different taxonomy for every world (and I’m conveniently ignoring the idea of panspermia, which doesn’t really help things since life will still take a completely different evolutionary direction after each world is seeded), but especially for simple life like this, it’s probably reasonable to use the same definitions for things that have a similar form and function. Most colonists (and players) probably aren’t going to care.
Many of the early life forms have common as well as scientific names. Cnidarians (jellies) and Echinoderms (marine invertebrates such as sea stars) evolved early on and there are thousands of different species of them. Currently, I use the scientific classification here, because it makes it easier to break things up into general categories.
The term echinoderms is very specific, probably a bit too specific to use for exo-life, but ‘marine invertebrates’ also covers jellies, crabs, squid, molluscs and other things so is quite broad, and ‘sea stars’ is too specific. I’m thinking of moving to less scientific terms, but haven’t yet come up with a nomenclature which works.
Things That We Grow
For worlds which have evolved to a much later stage of evolution, specifically those that have reached the Simple Land classification, there will be plants growing on land. Of course I use the term plant in the most general way, since it is thought some of the earliest land based species were fungi – which aren’t plants.
If a fungus-like organism grows on an exo-world then can it be called a fungus? Colonists will probably call it that, especially if they look like giant mushrooms, though their scientists will probably complain at the improper (or complete lack of) use of taxonomy.
Fungi, grass, trees, ferns and similar things will use broad definitions that are used by common people to refer to a type of thing. It it’s tall and vertical, doesn’t move and can be chopped down to produce a hard material that can be used for burning or as a building material, then it’s a tree. If it covers the land, is green and can be grown on farms to produce seeds which can be turned into bread, then it’s probably a form of grass.
Fruits and vegetables will similarly be classifications of products that can be farmed and eaten from such worlds. They may have only a passing resemblance to Earth forms, and exist no-where in our evolutionary tree (though colonists may have brought their own varieties), but most people will probably consider them the same thing.
I’m also assuming that these exo-organisms can be eaten safely. This may or may not be true, but it greatly simplifies things without having to assume every useful world has either been the subject of some form of panspermia, or has been heavily terraformed by colonists. It fits the typical Traveller-like SciFi setting better if colonists can just drop down onto a verdant world and start farming the local plants and eating the local animals.
Things That We Pet
Insects will be small invertebrates that crawl on or fly above the land. They will probably evolve on most worlds, and like on Earth form countless different species which are just as annoying but also vital for many parts of the ecology. However, only scientists normally care about exactly what they’re called, except for the ones which are venomous or bring disease.
But above all of those in terms of size are the real animals, which are probably the most complicated simply because humans form an emotional attachment to them. Birds, mammals, lizards etc are classifications that apply to groups of species.
If it has feathers and wings, we will probably call them birds, even if they aren’t descended from non-avian dinosaurs.
What about large herd animals which are good for eating? Do we call them cows?
Four legged warm blooded furred predators which are friendly towards humans? Dogs? Or Cats? Are they even mammals? What if they have six legs and have a pouch? I’m currently failing to come up with a classification scheme that I like. In one direction lies blandness, in the other horrendous complexity.
The normal high level classification of mammals, lizards, dinosaurs etc doesn’t really work, because these are genetic classifications with specific traits, and the prominence of these type of animals means that players are more likely to notice the disparity.
It might make sense to classify by herbivore and carnivore, and maybe size. Maybe one world has a lot of “Gigantic Herbivores” (which look a bit like dinosaurs), and another mostly consists of “Small Amphibians”. Meat from “Gigantic Herbivores” is considered better quality than meat from “Small Amphibians”, and possibly there is a market for live specimens of the former as well (and especially for Gigantic Carnivores). The main purpose of defining all of this is to feed into the trade system after all.
Traveller has some charts and tables for this sort of thing, but I haven’t decided whether these are at the right level of detail. GURPS Space also contains random creature creation charts, but this is probably too low level for what I need.
So I still need to think about this, and whatever I come up with will probably change at a later point.