I see a danger to the future existence of the human race, and it is the kind of thing that people should think about and prepare for now. Sometime in the next 50 years machines will be smarter than people. There are major technical hurdles to overcome, such as the inevitable end of Moore's Law, which probably mean that it is not right around the corner or even within the next couple of decades, but it will happen, and easily within this century. And if for some reason it does happen within the next couple of decades then that means the results will be upon us that much sooner.
We can predict what will happen next and follow it to its logical conclusion, which is a future without people.
As machines become smarter, people will become increasingly reliant on technology. We can see that already with smartphones, which only have been with us for barely over a decade. Eventually machines will do all the heavy mental work, which will make our lives easier, but also make us more dependent.
And since we will be so dependent on the machines, we will start incorporating them into us. This will evolve over time until we are no longer purely human, but human machine hybrids. Perhaps when your biological brain dies, the machine part of you will be able to continue with all your memories intact. Maybe it would have an artificial body or maybe it will exist in a virtual world. It is likely that some would prefer to live in a virtual world where they can do more things than they could in the real world. Taken to the eventual extreme, our descendants would no longer bother with biological bodies and prefer to exist as machine intelligences either in the real world or in virtual ones.
The evolutionary pressure will be against purely biological people. Having machines incorporated into you will make you more productive, competitive, and increase your quality of life.
The future I describe might be long distant, but if it is not the future we want for the human race then we should start thinking about it now. Maybe we could have a Pure Human movement that would prohibit the merging of machine intelligence with human intelligence? This could be roughly analogous to the current legal ban on human cloning, because we very likely have the technology right now to clone humans, but countries ban it because they are uneasy about the implications of where that might take us.
However, we might not be able to prevent it. Linking machines with human intelligence is likely to happen in such small steps that we will easily adjust to it. It is sort of happening already with our dependence on computers. It could also start as a series of military applications where having the most effective soldiers determines who wins the wars. And once the genie is out of the bottle, we will never get it back in.