One article asks "Are Humans Still Evolving?", another answers "Humans Will Not Evolve Further", one asks "Natural Selection Not The Only Process That Drives Evolution?", while yet another exclaims "Natural Selection May Not Produce The Best Organisms", and finally as one says "Darwin Had It Right".
Notice some of the obviously conflicting statements in these articles:
"Survival of the fittest" is the catch phrase of evolution by natural selection. While natural selection favors the most fit organisms around, evolutionary biologists have long wondered whether this leads to the best possible organisms in the long run. [article 1](ibid). Debate is even developing around the issues resolved or not resolved by Darwinius and Afradapis, two finds this summer. It seems clear to me, then, that the teaching criteria for determining what is "the better" is what is drifting, evolving, or at least changing.
As part of a working group sponsored by the National Evolutionary Synthesis Center in Durham, NC, the team of researchers decided to find out if natural selection — a major driving force of evolution — is still at work in humans today. The result? Human evolution hasn't ground to a halt. [article 2]
The results lead to the provocative hypothesis that, rather than being the result of Darwinian selection for new adaptations, many of the genetic changes leading to human-specific characters may be the result of the fixation of harmful mutations. This contrasts the traditional Darwinistic view that they are the result of natural selection in favour of adaptive mutations. [article 3]
You may want to read some other concepts of other top scientists about where human evolution is heading; will we evolve into robots or into super human beings?
There is no set formula to determine, to use Darwin's approved language, "the fittest", if these fundamental questions are still perplexing to scientists.
One thing is sure, the criteria are biological considerations based upon this planet alone. The criteria, therefore, tend to be geocentric like they were when the earth was thought to be the center of the universe.
There are greater determinants, which seal the fate of species on planets orbiting central stars, than the singular and quite limited notion of biological evolution.
According to the Tenets of Ecocosmology, biological evolution on habitable planets is by no means the greatest factor in passing "The Test".
That test must be passed via memetic evolution in order for sentient species to avoid extinction in this cosmos, even after having avoided extinction on a habitable planet.