Humans, Humanoids, Animals, Plants (CPrH)

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At some point in the history of the gods, they probably created all living things. (It's possible for the flora and fauna of the world to have been created by some other factor. For example, they might have just been there when the great ice-cap melted. But it's a more common element of the story that the gods created them.)
This creation process might have involved an accident; for instance, the greatest god sneezed, and blew fully-formed living things all over the world.
More commonly, it's a deliberate process, and the gods or one particular god methodically created all the living things known to man.
When working up this aspect of the story for his own campaign world, the DM can use this to help define the way the gods look upon specific forms of life. Was Man created so the gods would have something entertaining to watch? To fulfil a higher destiny? So that his brightest and best might one day add to the ranks of the lesser gods, or accompany the gods on one last, great battle? This kind of decision helps define man's view of the gods and their requirements of mankind.
It can also be used to define mankind's opinions on certain matters. If, for instance, animals in general were created to serve Man, then Man might have little regard for them, except as pets and beasts of burden. However, if each god created one or more animals to serve as totems for the god, then Man might have a lot more respect for certain animals.
If the story of creation says that one sex of the sentient races was created subordinate to the others, then there will be a crushing social pressure to keep that sex "in its place." If the story of creation does no such thing, then any such attitudes will be have been created by mortals and may vary from place to place. Additionally, with the added complication of several sentient races around (humans, elves, dwarves, etc.), the DM can make this decision several times and choose a different approach each time. Perhaps, on his world, dwarves are strongly male-dominated, elves are female-dominated, and humans are more or less equal? Any such arrangement is possible.
Note, however, that when one sex is oppressed, players are less likely to want to play members of that sex. Few players want their escapism to involve this sort of prejudice directed at them.