In my setting the humans live in the shadow of the now mostly extinct older races.

Elves basically created their own rapture by using magic and creating porotal to paradise. The entire species would move in and seal the gates behind them forever the absolute worst among them. Still long lived these ‘Fel’ now change and warp as the unseen magical infostructure that was the key to their species succuss now falls into ruin and their imbued bodies take new forms. It is often that humans worship the Fel as what remains of their power can affect crops or be used to ward of the large creatures at night. Their bodies are now things of nature and take many forms, an entire forest could actually be part of a massive collective conscious of a single Fel.

The Giants came next and where short lived compared to the others. They understood magic that allowed them to create the massive cities that still stand today. They even created creatures carved from stone and turned to flesh. The dwarves where a servant race meant to aid in making their ever-growing cities. But for all their achievements it was a plague ripped through the population destroying them and leaving behind their cities and their slaves. Today these cities are mostly inhabited by humans building homes among the unbroken ruins taking advantage of the aqueducts and the city’s natural defenses to set up their own small kingdoms. One of these is the heart land of the sprawling Twilight Empire.

The dwarves survived their masters. The magic within the cities still had its effect of making them docile and weak and they left and built their one settlements carved from stone. Immortal but unable to breed or create more of their kind and facing the seemingly endless attacks by the orcs the dwarves knew their species was doomed. This is perhaps why they took interest in humans who had formed their own small civilizations dotted around the safe proximity of the dwarves’ mountain kingdom.

It is unknown what caused the great madness that caused every dwarf to turn mad and started going on killing sprees until their species was no more. But their work still stands and today most of their cities are avoided as the living remints still stalk the very depths of their moutainhomes. However, most human culture can be traced back to the dwarves who had taught the growing human civilizations how to build, craft and use magic.

The orcs have been around before the elves even existed, but an alien virus took over the whole species and now they all serve a single dark master said to live in the furthers most remote regions of the world. Their vast armies march out to destroy any rival civilizations however the coming of the dwarves nearly destroyed them. There numbers are recovering however and today they face humans another short lived race that can breed and multiply even faster then they do.

Most of the peoples in Aedelor, the world my partner and I work on, were created by gods either directly or indirectly. Souls are real and inform the ancestry you will be, and gods tinker with souls to create new kinds of life. Very rarely, non-god entities have been able to do this as well, most notably giants and dragons have both achieved the feat in different methods.

There are only two sapient species in the Lonely Galaxy, humans and yinrih. There is a closely related non sapient species to the yinrih, closer even than chimps are to humans, and the question of why the yinrih are sapient and the tree dwellers are not drives a lot of philosophizing on the yinrih’s part. The Atavists in particular resent the burdens of existential dread and moral guilt that come with having a rational soul and wish to return to being irrational animals.

In one of my settings, this is taken into account, sort of. The world spans ages. In the first age, magic is so plentiful that entire species, at various levels of sapience/sentience, were created by random accidental acts of magical creation. By the third age, most have disappeared, leaving areas dominated by single species. By the fifth, only non-magical life remains, just humans, and there is no sixth.