The aliens of the Mystaverse may also reveal more of what the pre-Mars society was like. The aliens may be alien only because they are different from the accepted norm, not because they evolved independently. Given that the majority of the aliens thus far revealed are variations of the humanoid form it may be that they are basic human stock, modified to work in different environments. After civilization fell they were basically abandoned and left to fend for themselves and it is now, an unknown amount of time later that the various races are large enough in number or advanced enough to exercise a certain independence from their previous employers/masters. It may be that the criminal, subterranean and centaur creatures of the previous chapters are emerging as a force who want the advantages the rest of the populated planets further along in their recovery are enjoying.
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