Humans are a species from Earth.
Many Spore users have tried to create Humans using the game, but they often struggle because, although Human parts are available in the Creature Creator, it is difficult to make them to fit the exact appearance of a real-life Human.
Some players report finding user-made Human Empires whithin the vicinity of the Sol system. It is unknown whether this is a coincidence or observation bias, or whether there is a feature that causes creatures named (or tagged) "Human" to appear in that region of the galaxy, in a similar manner which causes simpler creatures to appear in the early Creature Stage.
It is also unclear whether (by the time you reach Earth) that humans are extinct or it was before they "came to earth". The age of Earth, however, can be measured by the difference in distance between the Earth and The Moon (Earth) - but because of the unreality and inaccuracy of the game, it is still impossible to measure the distance, as it would be not be accurate. Also, it would have a low possibility that the designers of Sol would have been accurate, as it was an Easter Egg. Also, further investigation reveals that many features of Sol (Asteroid Belt, etc.) were not featured in the first release. The asteroid belt was included in a later update, but other factors still remain missing.