> Now that we are over 6 billion humans on earth, with migration way easier and common place than before, shouldn't on the contrary human evolution been speeded up ?
Evolution speeds up as a result of either an increased natural mutation rate or extreme environmental challenges (lots of death produced by unfitness) -- or both. But we're not seeing either in modern times.
> EDIT : I know evolution is not progressive but happen by sudden steps ...
No, this isn't true as a rule. In evolutionary theory, the overall rate of change,and the presence or absence of abrupt changes, is entirely dependent on what produces greater fitness. In other words, the rate at which evolution happens, and the shape of the change curve, are themselves driven by considerations of fitness and natural selection.
Evolution speeds up as a result of either an increased natural mutation rate or extreme environmental challenges (lots of death produced by unfitness) -- or both. But we're not seeing either in modern times.
> EDIT : I know evolution is not progressive but happen by sudden steps ...
No, this isn't true as a rule. In evolutionary theory, the overall rate of change,and the presence or absence of abrupt changes, is entirely dependent on what produces greater fitness. In other words, the rate at which evolution happens, and the shape of the change curve, are themselves driven by considerations of fitness and natural selection.