In my novel most species of animals and plant life have gone extinct, and they have to be created again. Some of these reborn animals and plants are old and others are supposed to be brand new species. I know what the purpose of the new flora and fauna will be, but how would I go about designing them? I know ill have to do my own research, but any advice on how to get started?
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The way I would do this is I would start by asking myself, "What kind of environment do these new species inhabit?" For example, I started writing a book last year set on a barren desert planet, and so I needed an ecosystem that could potentially exist there. The next step is to think of several features that would benefit the inhabitants of your environment. In my example, I created wolf-like creatures with thick matted fur to protect from sandstorms. Then you can extrapolate from there. Often it is easier to take an existing creature (like the wolves) and adapt them to the environment, rather than creating a completely original creature. This can also help your audience visualize the creature because they already know what it looks like. I can give more specific advice, but this answer is getting long :)
Energy In - Energy Out = Storageis the most important rule
- Nature doesn't care about divisions between species or individuals. Design things that make sense without it
- Avoid teleological worlds: If your fauna has a "purpose," hide it a much as possible.
- Use tools from your life to build worlds. It's more efficient that way.
I find it very important to look at energy balances.
Energy In - Energy Out = Storage. It's a fundamental rule of physics, and utterly essential for living creatures. More interestingly, storage is limited. We can't just keep storing more and more energy. You can store a lot of energy in fat, for instance, but at some point you become heavy enough that mobility becomes an issue. Living creatures are constantly trying to spend the energy they get.
This is also very important to avoid telelogical planets, where the "purpose" of each new species is so evident that you can't believe they are real. The only sure fire rule for species is that if you can do the same job in a different way, and use less energy, they'll find a way to do it. Thus your job as a worldbuilder is to bury every "purpose" you came up with into this goal of being more efficient with energy. It's the only truly believable "purpose."
Another key trick is to remember that nature doesn't have a concept of species, or of an individual. We draw those lines as humans, as we try to make sense of the world. Try to make it so that your species is not so much a "species" that is "doing things," as much as it is a gestalt of the individuals within that species. It may make sense to have a worker bee sacrifice itself for the good of the hive, if we're thinking about the hive. But that decision to sacrifice itself has to be made by the bee itself. It needs to have been structured to make that self-sacrificial decision. (spoiler: We're still not entirely sure how this works)
Another classic example of this gestalt way of thinking is tree branches. The current prevailing model of how trees grow is that each branch grows on its own, oblivious to what any other branch is doing. The only exception is that one branch may use hormones to signal that it is a primary branch, which gets to grow straight up (Forming a trunk). And the branch spawning process is typically rather random. So while we may see one tree, it operates more as a set of 10-20 branches that all happen to have the same roots.
Beyond that, you really have to look at your own style. Myself, I enjoy Chinese philosophy, which is heavily centered on balance and harmony with nature -- exactly what you need to build a world! Accordingly, I tend to use the tools I already have available to me. I'll use yin and yang to model the ebb and flow of energy. I'll use the 5 elements to model the interplay between different species. Then I'll use their interplay to create all the excitement I need. When I need a sense of purpose, I'll use the daoist cosmology to provide a wuji and taiji. For inspiration, I can model it using the I Ching.
Some of those terms may not mean anything to you. They don't need to. They are the tools I use. Why do I use them? I use them because they're efficient for me. I already chose to learn how to use these tools in my life, so using them in my worldbuilding is almost free.
Remember the opening rule? The only truly hard and fast rule? Creatures will always find a way to do the same thing with less energy? Chinese philosophy happens to be a low energy solution for me. You have to find what makes sense to you. Maybe you are an expert at musical theory. You can craft a world based on the way chord progressions are constructed. Are you a painter? Think in terms of media: a watercolor world feels different than an acrylic world.
As long as you make sure
Energy In - Energy Out = Storage, the rest is entirely what is most convenient for you. Beyond that, the art is in hiding your own brush strokes. The less obvious it is that you crafted flora/fauna with a purpose, the more believable and beautiful the world is.
(Oh, and I use StackExchange to help build my worlds. I'm just saying... use what feels natural to you, and takes as little energy as reasonable.)