I took a race, humanoid in basic form, and fragmented it into four groups that, because of the life habits they chose to lead, they evolved in four drastically different directions.
Like all bipedal creatures we are most familiar with (humans), they farmed crops, herded an assortment of livestock, lived in wooden structures of a log cabin design, and so on - your average very early western settlement, so to speak.
On this world, the trees are immensely tall - maybe something like our redwoods, only rather than being only something akin to a spruce tree, they all were this tall, even the fruit trees. SO - one quarter of the people took to the trees in search of the fruit up there, and since it took so long to climb up there and back, not to mention hauling their harvest around, they took to living in the trees all the time.
And as we all know, there are those people who simply must climb mountains, so I made the mountains in my world viscous crags that were much easier to attain on the wing. Now since wings aren't really an evolutionary trait I can see spontaneously developing, the root race of this planet may have been winged to begin with and only those who remained in the mountains retained their flight ability. I did make them all egg-layers with many of the nesting characteristics of birds. Who knows, maybe severe mountain cold drove many of the people out of the mountains and only the hardiest remained. Then, after generations of life on the ground, wings atrophied away.
That leaves the fourth and last quarter of this fragmented race. As in all peoples there are those who might be called the criminal element. As life becomes rather specialized, the selfish and mean, the greedy brutes, bullies and other such personalities were ostracized. Unwilling to do the work to pick the fruit or till the fields, they took to hunting within the fringes of the great forests, and they hunted anything that moved, to include any of the other humanoid members of their world.
The tree-dwellers I came to call Eanders. They were frail but very strong and ghostly white in appearance with an elven beauty.
The people of the mountains I call Winders. They were tall, fine-boned people with an average wingspan of around fifty feet. They built grand open stone structures and hunted the tops of the trees or the open plains.
The farmers of course were named Landers. They lived near the fringe of the forests walking a fine line between the demons who stole their livestock or the unwary citizen and the plains where the Winders hunted whatever they could swoop down on and carry away.
Then there was the Honders. Raised in such a way that only the strongest of their young survived to procreate, they were heavier than any of the others. They were the most brutish and unforgiving of all the peoples.
Despite all these physical differences, and the obvious hate or fear each has for the others, they all have quite a few similarities.
They all have bony stingers located on the inside of their wrists at the base of their palm. Per race, these had also evolved differently. The Winders were highly poisonous; prey needed to die instantly if they were to successfully hunt on the wing. Eanders poison wasn't so vital to their survival but it did paralyze. Being blood-drinkers rather than water-drinkers, Honders' venom was a strong anticoagulant, which in itself was fatal enough. The Landers also had the barbs but their poison cause a wasting infection that might cost a victim to lose a limb if the sting went untended too long.
They also had spinnerets located between their thumb and first finger, but the uses of their webbing was drastically different per race. The Eanders were by far the most talented:their homes were spun into a hollow ball, which they camouflaged with the leaves of their host tree. It lasted a lifetime unless damaged. The Landers were next in proficiency; they spun all their clothing and material. The Winders could also weave but they did little more than create their sleeping nests. The Honders used their webbing to bind their prey until they were no longer of use alive, or they make sacks to transport or store meat.
As I mentioned before, they all laid eggs that looked something like a turtle egg, about the size of a softball. At first the outer membrane is transparent and the yellow yoke is clearly visible. As soon as the male fertilizes it (after being laid) the membrane turns white. How the egg is tended after fertilization is drastically different per race.
At any rate, I had a lot of fun creating these divergent races, while at the same time tying them closely together. You see, the plan for the story is to end up with one young man who can claim blood ties to all four of the races, and then just maybe bring them all back together, maybe not to live, but at least to work together rather than hunt or prey on each other.
So how did I do that? Well, when I finally get it all written, you'll find out.
Out of curiosity, how would you manage to pair these four races together? You gotta have two of them somehow create a girl and the other two somehow create a boy, at about the same time, and somehow this girl and boy should fall in love (an important step, I think) and create the child who will try to bring peace and understanding, or at least cooperation between all four of the races. Who knows what that will start.