An interesting syndrome called "Unertan Syndrome" is shedding light on the evolution from quadruped to biped, and this in turn sheds light on the possible future of human evolution.
Until recently, scientists all believed that many genetic mutations were required for humans to evolve gradually over a long period of time from a quadruped (walking on four legs) to a biped (walking upright on two), but some families have been discovered in Turkey who challenge this assumption. Several members of these families have a mutation in a single gene, and as a result they are quadrupeds, walking on all fours. They sit like apes, holding their heads forward. They are able to stand on two legs only briefly. Furthermore, they are ape-like in having a very primitive language, and mental retardation.
Could the change from quadruped to biped also have been the result of a mutation in a single gene? If so, the change could have happened over a single generation, as the devolution to quadruped has happened in these Turkish families. Since these individuals have lost articulated speech, it is also quite possible that a single gene is responsible for our ability to walk upright and our ability to develop a vocabulary greater than six grunts.
If a mutation in a single gene can produce such massive changes in a generation, what mutations might occur in the future that could change the human race entirely? The discovery of Unertan Syndrome makes assessing the future of human evolution next to impossible.
The theory of evolution as we know it depends on the concept of "survival of the fittest", but in the Western world at least we have more or less removed this effect, since survival no longer depends on fitness. Humans are nevertheless changing - in the West we are growing taller and living longer - but this is more to do with changing food supplies than "evolution" as we understand it.
The existence of Unertan Syndrome, however shows that, in these Turkish families at least, the children have devolved in a generation from intelligent bipeds to unintelligent quadrupeds, without "survival of the fittest" coming into the equation, and without natural selection. There is no reason to suppose these individuals will not have offspring who are also quadrupeds.
Evolution is not fully understood, and discoveries are made all the time that force scientists to modify their theories to incorporate the latest findings. This makes the assessment of human evolution (or evolution of anything else for that matter) impossible, or little better than pure speculation.
It does seem likely, however, that survival of the fittest may become a real factor in the future if climate change becomes extreme. Perhaps we will all end up on all fours crawling back into the jungle to escape the heat!