As you think about our aliens, ask yourselves what problems your aliens face. If life is easy and problem-free, your aliens will have no reason to evolve. Here are some sample problems that might challenge your aliens.
Seasons affect the food and water available to life forms, and produce temperature fluctuations that may be life threatening. Periods of flood and famine may intensify competition for food, and icy winters make food hard to find.
Normal seasonal variations may be intensified unpredictably by large volcanic eruptions and asteroid bombardments. When the air is filled with dust and soot, some of the energy from the system's sun is prevented from reaching the planet. This causes colder temperatures and a reduction in the food supply. It is believed that asteroid collisions may have caused the mass extinctions seen in the fossil record on earth.
Weather varies within limits from season to season. Climate puts limits on the variation possible in the weather of changing seasons.
Climate may also have very long term, rhythmic variations, such as ice ages that come and go, or periods of global warming that cause deserts to spread and seas to rise.
Fierce, powerful predators can terrorize prey populations. Their unpredictable attacks can remove individuals, sometimes key individuals, from evolving populations. Constant fear can monopolize the mental energies of a population, making it difficult to plan beyond the emergencies of the present.
Competition from Other Groups or Species
When groups compete for limited resources are
Diseases and Parasites