The unwanted children of...

What if the whole human race was an accident or never intended to exist? the "sacrifice" at the beginning, maybe it was an execution of a criminal from the home planet of engineers and his elders wanted to see him off for the last time. He was probably someone of importance to have a lot of folk at his sacrifice or death sentencing. after his death, the first humans spawned from out of nowhere and grabbed the attention of the engineers and saw us a little pet project. they interacted with us and tried to teach us a lot of things hence the cave paintings. eventually human nature kicked in and we started to kill each other in favor of the engineers or simple enough, the others persons land or resources. Embarrassed and ashamed of their pets, the engineers thought it be the best idea to just put us down and end our pathetic lives.