In reply to a question on the discussion forums of this Coursera course: Introduction to Genetics and Evolution. Check it out.
Evolution is just change over time. It can be good or bad, it can also make the individuals unfit to the environment they live in.
This is because the driving force of evolution (the main one, in Nature) is natural selection (survival of the fittest). This makes us think that “Evolution makes species better”, because in our point of view (we are animals, after all) surviving as long and as healthy as possible is a “good thing”. We put morality over the evolutionary process.
Think about dog breeding. There is another force, stronger than natural selection: human intervention. We let reproduce only dogs that have the feature (or a part of the feature) we want the final breed to have. This regardless of how fit the final dog will be in his environment, ie regardless of how many years he will live and how many illnesses he’ll be catching.
The final result might be the dog we wanted (eg, pink-colored, with pointy ears and small as a mug), that will maybe leave 5-6 years with plenty of tumors, heart problems and the such.
Now, back to the humans. In our case it’s exactly the opposite of dog breeding. We are reducing, over time, the power of natural selection (even the “unfit” survive, and we all fight daily to make this happen), we luckly do not have artificial selection (some bad guys in the past had this idea though, I guess you know who am I talking about).
If you want, you can still talk about “human evolution”, in the sense that humans change over the generations (for example, there might be temporary “unintentional artificial selections”, where only super-nerds get to marry and make children and the super-muscled are left alone because of a TV series…but that’s not going to last long enough to actually make a difference And it differs from country to country, anyway).
The truth is that we are just “accumulating mutations”, because the selective pressures are all flattened out. Where this will lead us, we can only guess.
My bet is that we’ll soon be able to modify most of our genomes, making us fitter than ever (I’d like to live a couple of thousand years, for example, being able to run a marathon the month before I die). But it’s only my hope.