On a Spore planet, the native life forms are so different from humans that they look like aliens.
Although you can see no physical differences in their bodies or faces, there is an obvious difference in their behavior.
While on Earth we usually feel comfortable interacting with other people who have similar cultures to our own, it's not the case for other species.
On a Spore planet, it would be difficult even to speak the same language, let alone understand each other.
The indigenous life forms on a Spore planet (including humans) develop separately from one another and are genetically incompatible.
These organisms do not interbreed. They cannot produce offspring together because they don't share any genetic material.
