True most creatures on earth have two different sexes but with most you can't tell if its a female or male without getting up close. I mean a horse is a horse, you don't know which kinda unless you really get up close(not that you'd want to). I know there are creatures like lions or cardinals with distinct differences but if you're talking about having different organs on your creatures than I don't think you're in luck. I don't think spore will get that detailed. You might be able to change the color scheme or certain designs on your creatures to differentiate between genders but as for now it looks like all your creatures will be look-alikes.

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