What would be a good thesis statement for an essay on this story?
To pick an interesting thesis statement you really need to think about the central themes of the story. Once you have identified those central ideas or messages of the story you can base an appropriate thesis statement around one of those. To me, the major theme of the story is the dangers of unrestricted scientific knowledge and man's inability to use that knowledge for good. This is based around the striking quote:
Perhaps, in the old days, they ate knowledge too fast.
Clearly the story paints a horrific dystopian picture of what could happen with the ever-daunting power man gains through science. Therefore a thesis statement could be:
The further advanced scientifically mankind becomes, the quicker our destruction as a race will occur.
Other themes that can be identified are the coming of age theme, truth and how we relate to it, and lastly, civilisation.