Building a Universe

Biology

The type of life that exists on your world is determined by the answers you gave to the questions about geography. I can think of four fairly important factors to think about when trying to decide what sort of life is on your world: water, energy, climate, and other organisms. There may be more, but for me these four elements seem to affect the life on a planet the most.

Scientists say life needs water and energy to thrive. The amount of each of these determines the kind of organisms that inhabit your planet. A frozen ocean like the one that might exist on Europa might only be able to support tiny microbes, while the oceans of earth teem with a wonderful variety of life.

Climate also affects the type of life on your planet. Climate is the average temperature of a place on a planet and is determined by a planet's proximity to its sun(s), the type of orbit around its sun(s) and the amount of wobble, spin and rotation the planet has. On Earth at least, the climate is warmer the closer you get to the equator or the closer you get to sea level. The climate is cooler the closer you get to the poles or the higher you climb in elevation.

An organism does not usually exist alone. They usually exist in an environment that includes hundreds, even thousands, of other organisms. Each of these organisms are competing with each other for the water and energy they need to survive. Some organisms draw energy from a sun, such as plants, while others get their energy by eating other organisms, such as herbivores eating plants and carnivores eating other animals. This means that over time, organisms evolve into forms that help them to get the water and energy they need while preventing them from becoming something's lunch.

Tool-using beings, such as humans, have a huge impact on the biology of a planet, especially when their populations grow. Humans have reshaped the life on this planet, causing entire species to go extinct, such as the mega fauna on the North American plains, while providing ideal breeding grounds for others, such as rats and squirrels. It's important to note, however, that organisms go extinct all the time. Tool users seem to do it faster and on a larger scale is all.

With this in mind, here are some questions to think about when you're populating your world with life:

What sort of plants live in each of the climates you created? How big are these plants? Where do they get the energy and water they need?
What sort of animals live in each of the climates you created? How big are the animals? Where and how do they get the energy and water they need?
What kinds of microscopic organisms, such as bacteria and viruses, exist on the planet? How do they get their energy?
Are there forests, jungles, marshes, tundra, etc.? Where are these located? What sort of plant and animal life exists there?
How does the climate affect the life on your world?
Are there a large number of tool using beings (like humans) on your planet? How have they changed the plant and animal life? What organisms thrive because of the tool users? What organisms are going extinct because of them? What organisms are extinct because of them.

Once again, this isn't an exhaustive list of things to think about, but it should get your brain storming going.