When most people try to answer this question they use their intuition. They assume that change happens at the same rate they have witnessed it happening based on their narrow experiences. History shows that change has happened at an expotential rate. Life formed 2 billion years ago hominids 6 million years. We've been around as a species for 100,000 years, had agriculture for 10,000 years, scientific revolution was 400 years ago, industrial revolution 150.
Looking at this sort of trend from a variety of perspectives leads to this conclusion about the nature of change.
What is interesting is that given trends involving moore's law, brain scanning and nanotechnology it seems likely that we will very shortly hit a point where change happens so fast we can't follow it. So I dont neccessarily think that we can conceive what life will be like in 50 years but I highly doubt humans will be the dominant species.
I really cant say enough do this topic justice. There was another thread where the seasteading institute was mentioned. Peter Thiel, the man who funded that institute to the tune of half a million also funds the singularity institute. They are having a conference in NYC this October that I will probably attend. I find the topic very interesting.
http://singinst.org/