How To Build A World In Seven Days

Actually, it will likely take more than seven days but I thought I should copy the catchy title format that other blogs used. I can’t promise to “blow your mind” with the information but I will try.

Source: dirkb86

Fundamentally, world building is an act of creative fiction to construct a coherent but imaginary world. To varying degrees this is part of the process of creating TV shows, films and novels. Historically though, the most in-depth examples were probably from table top role-playing games where exploring an imaginary world was the focus of the game. Computer games have become more prominent examples in recent years though, especially in those games described as Massively Multiplayer Online Role-Playing Games (MMRPG). However, Tolkien’s Middle Earth* is perhaps one of the most well known examples and has featured in many books, films and games.

Since I am not a budding author, film maker or game designer my current interest in world building is really just an exercise for my own enjoyment. It sprang from an interest in astrobiology and speculative evolution and my own thoughts as to what life could be out there in wider universe. For this reason, I have decided to focus my world building on the possibility of life on exoplanets around distant stars. This gives me an excuse to read the latest developments in the scientific literature on appropriate topics to ensure that my speculations are somewhat grounded in current scientific thinking.

World building related to speculative evolution could be performed from the top down where a specific creature is first designed and then the wider environment around this creature is revealed. This is probably suitable for artists who produce a drawing first and then choose to expand on this later. However, my preference is for a bottom up approach which starts with the physics of an exoplanet orbiting a star before determining the possible environmental conditions and the life that might evolve there.

Therefore for my approach I will need to consider in turn the following seven steps. This sort of structured approach may perhaps be helpful for others, though obviously alternative methods will work too.


Since I am a physicist by background, this first step is the one I am most familiar with. This is about defining the star system in which the planet resides.

  • What type of star or stars are present?
  • How many planets are there?
  • What are the planets made of?
  • Do the planets have any moons?
  • How do all these celestial bodies orbit each other?


The second step is strongly linked to the previous step but only focuses on a single planet (or moon) in the system to determine the environmental conditions. This helps to identify what challenges life on this planet might encounter and how much biome diversity there might be. 

  • How much illumination does the planet receive?
  • What is the atmosphere made of and how much of it is there?
  • What is the climate like?
  • Are there seasonal climate variations?
  • How deep are the oceans?
  • How strong are the oceanic tides?
  • Is the planet volcanic?


The third step is to consider how life began from non-living matter on this planet. This is a mix of chemistry and biology and not an area I am very familiar with. Since the process by which this occurred on Earth is not known for certain it may be impossible to say anything definitive about abiogenesis anyway. Considering this may provide some inspiration on the nature of the early diversity of life but perhaps in practice it doesn’t require much speculation unless you want hardcore technical realism.

  • Where did life begin?
  • Is it based on cells like Earth life?
  • What was its energy source?
  • What does it use to store genetic information?


The next step in a bottom approach once life has begun is to consider the broad categories of life known as domains in the traditional biological classification scheme. On Earth the three traditional domains are archaea, bacteria and eukaryotes. However, more generally, this step could include a consideration of whether viruses or prions can be included. In practice, a simple two domain system consisting very approximately of small producers (i.e. prokaryotes) and larger predators (i.e. eukaryotes) might be sufficient.

  • Do virus equivalents exist?
  • Are all cells the same?
  • Do more complicated organisms have a nucleus equivalent?


On Earth there have been various attempts to define “Kingdoms” of life within the biological classification rank below domain. Traditionally (in the UK at least) this was taught as five kingdoms: Animals, Plants, Fungi, Protists (i.e. other Eukaryotes) and Prokaryotes. Unless you wish to focus on the diversity in single celled life, this stage is really about macroscopic multicellular organisms.

  • How many kingdoms are there?
  • Is there a motile kingdom that eats other living organisms (i.e. animals)?
  • Are there multicellular primary producers (i.e. plants)?
  • Is there a kingdom that specialises in decomposition (i.e. fungus)?
  • Are kingdoms equivalent to Earth kingdoms or do they mix roles?


The next taxonomic rank below kingdom is phylum, the plural of which is phyla. In modern usage, genetic analysis is used to ensure that organisms within a phylum are more closely related to each other than they are to those in a different phylum. However, an older way to define a phylum is a group of organisms that share a body plan. This is particular useful when defining life on an exoplanet as you can quickly sketch out a range of phyla that cover the basic body plans.

Just to quote Wikipedia, on Earth there are approximately 35 animal phyla, 14 plant phyla and 8 fungus phyla. Examples of the larger animal phyla include: annelida, arthropoda, chordata, cnidaria, echinodermata, mollusca, and porifera. However, arthropods are often split into subphyla consisting of (approximately): arachnids, crustaceans, insects, myriapods and trilobites. 

  • How did early multicellular life diverge into different body plans?
  • What environmental circumstances caused this divergence?
  • In what order did the phyla diverge?
  • What is the shape of the phylogenetic tree that links the phyla?


Finally, I’m skipping over class, order, family and genus in the taxonomic rank system to get to the end goal of defining species. Partially this is just so that I have 7 steps but it also because real world biological taxonomy is rarely neatly categorised. In practice cladistics is the simplest approach but I still think it is useful to brainstorm a range of discrete phyla before creating example species within each. The final step is therefore the actual process of speculative evolution which is really the ultimate goal of all of this. Given the situation defined in the previous steps, what diverse life might evolve and how would it interact?

  • Does this species live on land or water?
  • What biomes can it be found in?
  • How does it survive the dominant local environmental conditions?
  • What does it eat?
  • What eats it?
  • How does it reproduce?

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