Human race is here all because it is part of an experiment being performed by a greater galactic race. The experiment was designed with various parameters in mind so that the subjects will only last for so many years un-assisted by their own technologies before their physical selves wear out. There are also other constraints put on life in general such as the constant needs for sustenance, oxygen, love, the idea of a greater being (or beings) than themselves, being grounded on the ground due to their physical form, etc. Some of the constraints were designed as limitations to test if life created by the experiment would eventually be able to overcome them. Other parameters such as hope, altruism, and faith were included as tools to help the subject race progress further into latter stages of the experiment.
The Solar System was chosen as the location for the experiment mainly because of its relatively remote location; a dark corner of the galaxy, so other galactic races will not likely stumble upon it by accident.
Early on, other parts of the experiment were carried out in other planets and natural satellites within the Solar system but they all eventually ended up with life died off in the early stages or ended up not progressing in the direction anticipated by the experimenters. Earth so far has been one part that has been able to produce the closest replication of what is deemed to be life that is (projected) advanced enough and is progressing in the proper direction that has a great chance to create technologies at some point in time to allow itself to escape the space it is originally confined to, in addition to the potential of transforming its physical self in the far future to another more advanced form to evade the eventuality of this physical universe coming to an end.
Not all has gone well with the experiment, however. A short while ago, a passer-by of a lesser galactic race had almost ruined part of the experiment when its chariot moved close enough to Earths space and was disabled by one of the barriers erected to cloak life on Earth from other space beings. The debris from its chariot had caused unintended spikes in technological progress of the subject race and more importantly provided concrete evidence of other more advanced beings. Another even greater compromise was the violation of the Non-Interference Principle. Far into the experiment, life on Earth evolved into the current subject race. Unlike all previous species life has created within this confined space, this new race has the natural tendency to deviate itself from set parameters. It has very peculiar ways of stretching and manipulating set boundaries to modify and mutate itself especially mentally on a large scale. In short it is the most chaotic version of life thus far on Earth.
About the chaotic nature of the subject race as mentioned above, it tends to magnify itself into some of the most destructive ways the experimenters have seen on this experiment scale. Its potential as a race that could last the whole experiment is constantly threatened by its aggressive and violent nature. Parameters that were introduced to safeguard life are constantly being twisted and combined in perverted ways to fuel its hunger for self-produced calamities.
Since in some sense the human race is the most promising part of this experiment so far, the experimenters are unwilling to allow it to destroy itself. A while back they decided to abandon their original role as the Clock-Maker and started allowing extremely limited interference when it is absolutely necessary in order to keep the subject race safe from itself. Seeds of philosophy, religion, deities, prophecy and life after death were introduced as additional parameters allowing the subject race limited abilities to subjugate itself and its destructive nature. Various deadly diseases and natural disasters are also injected periodically at the right moments to slow down the rate of expansion of humans. Advanced concepts in Mathematics and Science are intermittently revealed to the most promising humans pushing the subject race as a whole down a specific corridor to speed up the experiment progress and preventing the subject race from consuming all natural resources before having a chance to colonize other places in the Solar System.
The question that the experiment was designed to answer has always been HOW? Instead of WHY? Also, the experiment was designed to end abruptly when a certain result is attained by the subject race since beyond a certain point of biological and technological advancement the future outcome from that point on is always predetermined, for all galactic races that the experimenters have encountered so far.