Looking at H. Ergaster makes me rather worried about the future of our species...after all, we haven't been around nearly as long. What if we run up against an innate limit in our brains, and our technology can proceed no further? I doubt this will ever be an issue for our species. The beauty of culture is that it is cumulative and each progressive generation builds on the ideas of the previous. There may well be an innate limit in our brains that will not be present among children raised in a future culture in which our own ideas have been fully digested. As for Homo ergaster, I suspect that other factors simply caused their extinction before some threshold was reached for more advanced technology.
Similarly, I suspect we will cause our own extinction rather than encounter any technological celling.
Wow, whats with the missing tag? if any story ever deserves the "what could possibly go wrong" tag...