Evolution works by incremental changes, each of which to a first approximation must be at least neutral and preferably advantageous to producing offspring. In order for evolution to get from A to B, there must be a path of incremental advantageous changes to get from here to there. It can't magically leap from one optimum to another. So you see things like the way the same basic body plan is reused endlessly in the natural world; with only incremental changes available to create the next species, you can't create a whole new body plan from scratch, even if it would be completely appropriate due to, say, transitioning from land to water. It is also completely goalless; if there is a fantastic two-gene change that a species could make, even if both are individually advantageous, there's no particular force that will cause them to occur [1].
Evolution is both very powerful, with many people underestimating it, and profoundly stupid, with many people also overestimating it. Once humans really get cracking with the gene engineering (which has proved harder than we had initially hoped, but I'm still confident we'll get there), I'm sure we'll find a plethora of relatively simple changes we can make to natural organisms that may involve changing three or four genes simultaneously where no single change is advantageous, which is a thing that evolution essentially can't do.
[1]: Or at least, not yet... one bizarre-ish, "Selfish Gene" way of looking at human gene engineering is evolution evolving itself a way to make those multi-gene changes. Still not in a directed fashion, of course. But evolution will still apply to our own gene engineered creations, just possibly with a very different set of constraints, such as potentially severing the billion-year-old connection between fitness and direct biological reproduction... as I've said on HN before, you don't have to be a full-on "Rapture of the Nerds"-style Singulatarian to see that the future may get very weird....
Evolution is both very powerful, with many people underestimating it, and profoundly stupid, with many people also overestimating it. Once humans really get cracking with the gene engineering (which has proved harder than we had initially hoped, but I'm still confident we'll get there), I'm sure we'll find a plethora of relatively simple changes we can make to natural organisms that may involve changing three or four genes simultaneously where no single change is advantageous, which is a thing that evolution essentially can't do.
[1]: Or at least, not yet... one bizarre-ish, "Selfish Gene" way of looking at human gene engineering is evolution evolving itself a way to make those multi-gene changes. Still not in a directed fashion, of course. But evolution will still apply to our own gene engineered creations, just possibly with a very different set of constraints, such as potentially severing the billion-year-old connection between fitness and direct biological reproduction... as I've said on HN before, you don't have to be a full-on "Rapture of the Nerds"-style Singulatarian to see that the future may get very weird....