Please, and this is to everyone, please stop answering the poor kids post. There are lots of people who don't fully understand evolution (it's not the easiest concept either, for that matter, not if you don't know about it). It was an easy enough mistake, and could be taken to the following:
"Because the orcish race hunted the mighty Avarr for the feathers on their wings (they used the feathers in their dreamcatchers, headsets, and arrows. Mostly the arrows) the Avarr with wings lived shorter lives and had less children. It is also thought that those Avarr that weren't killed outright often had their wings broken by the Orcish hoards for pleasure and entertainment (Orcs are a brutal race). Eventually, thanks to the orcish hunting, the Avarr not only lost their wings entirely, but gained a larger, sturdier body. That is due to only larger, stronger, bulkier, and wingless Avarr being able to survive the hunting by the orcs, and also explains why they loath the orcs so much and sacrifice them to their sun god - they are trying to get their wings back by wiping out the orcish race. It is also theorized that their intellgence evolved to combat the hunting by orcs - only the smartest survived." - Book of Evolution, by the later burned for being a witch 'Darwin Galligos'.
To clarify, this is an actual thing - because human poachers wipe out about 5-10% of the elephant population for the ivory in their tusks each year only the tusk-less elephants are surviving to have young, leading to populations of tusk-less elephants across Africa (Bush and Forest Elephant) and Asia (Indian Elephant). As such, this is considered to be a viable evolutionary drive - hunting for a specific trait makes the trait disappear.