Enmos. There is certainly a limit to how smart we can become. Even machines do not work with "machine-like" precision as they become ever more complicated, as their parts become ever smaller. Our brain is supposed to be a fantastic computer but we are outperformed by basic computers on so many tasks because our minds have so many other things to cope with at one time and is at the mercy of the chemicals produced by the body. Diseases are still evolving and maybe one day, one of them will beat us. Extinction level impacts happen as does weather changes and environmental disasters caused by over population. I remember someone saying civilisations lasted about several million years according to his calculations so we would never find any "very old" civilisations in the universe. He maybe wrong though.