Incorrect. Humans are not perfectly adapted to our environment. That we can maintain numbers is not indicative of evolutionary "perfection". The Neanderthals were by all measures better adapted for the ice age than we were, yet in the end, we won out. Evolution doesn't just stop, that's a ridiculous assertion. Genes mutations don't just suddenly stop because we can maintain our numbers.
The fact is that evolution is not always a forward moving process. It doesn't make people be more complex or necesarily better. It's only goal is to maximize adaptability to an enviroment. There are plenty of cases where a human being would seem inadequate. For example: No claws, relatively weak muscles, takes a long time to raise young (most animals have some kind of chance at survival if you just dump them on the ground, huamn babies wouldn't last long. Most not all animals). Humans for the most part have no natural offensive or defensive abilities. However, there are two things that makes a human perfectly evolved for our enviroment and that is our brains and oposable thumbs. We don't need claws, tough skin, or any of the other specializations because we can think of a way to work around them or simulate them. The fact is that with a human brain even if the body is unsuited for an area (where it's too hot, where it too cold, ect.) we still survive. Take any animal grossly out of its natural enviroment into one vastly different it will most like die, do that to a human and its survival is dependant not on its body as an animal, but on its mind.
As for mutations stopping, no definitly not. Although it likely sounded that way from how I stated things. Evolution is not a one person thing, its not a small group thing, its a species thing. A single person gets a mutation that gene isn't going to be too important without pressure. If a gene is not needed (i.e. doesn't help the person have kids) then the gene will not be of any major importance. It'll exist but will have no strong prevelance.
I say evolution has stopped because our species is at the point where there is no reproductive pressure (save for constant widespread disease in an area, or reproductive problems) nearly any person on this planet that is capable of having kids can do so, it makes no difference whether their genes are of any quality. In smaller populations where food is scarce and predators hunt them, only the top most suitable 25% of a group might survive. That 25% is chosen on luck (I can't discredit this) and their genes. How strong are they naturally, how smart, how fast, disease resistent, aggressive, passive, ect. all matter.
Without such pressures then the "bad" genes and the "good" genes all exist in the pot. Evolution stalls because nothing is there to kill off the "bad" ones and to promote the "good" ones. If we ever get some kind of pressure back then evolution will pick up.
With sickle-cell, you are refering to what is called heterozygous advantage, which is a trait that evolves. Another example of this is found in Ashkenasi Jews, and evolved in the last few hundred years. Blink of an eye in evolutionary terms; humans are still evolving, and will continue to do so until we go extinct.
Some groups do have some pressures that lead to changes. Such as long standing disease in an area. In fact you can begin to see the results of this in Africa where Aids is so prevelant and being such a debilitating disease that some populations have developed resistance to the disease, some people seemingly unable to catch it. This is evolution in a way but until the whole species aquires these genes I don't know if that counts.
Evolution is a process, not a goal. The "final" state will be whatever state the last generation of humans finds itself in.
I will say this...ecological stress will accelerate our evolution, you are correct in this. But it has not stopped.
Evolution is a process but it has a goal that is reachable. Once a population no longer needs to change in order to reproduce sucessfully then evolution no longer does anything. As stated above there are places where changes are needed to reproduce successfully (like populations with high prevelance of aids) but they are for smaller groups, not the species as a whole. I say that evolution has stopped because what our bodies might be inadequate with, our minds make up for. As our technologies and knowledge advance there will be less and less factors stressing our population. New medicines to kill disease (thus preventing our bodies from naturally developing those defences), new fertility drugs or pregancy techniques (thus allowing genes that evolution would normally kill to continue). Our brains have slowly been making it so that evolution no longer works. Evolution is designed to make a species suitable to its enviroment. Humans now make their enviroments suitable to their species. Everything evolution does humans are now able to do or are working on being able to do. So maybe it's not 100% stopped but its only a matter of time.
