My knee-jerk response was to say, “Well, of course natural selection is fast enough, because here we are?” But I didn’t do that.
I also didn’t respond by taking out my Dawkins-certified religion-bludgeoning stick. I’m not partial to that pedagogical approach, and I figure it only got Dawkins uncomfortably familiar with Ms. Garrison of South Park.
Instead, I responded in what I think was a more helpful fashion, and my answer was not what the questioner expected. Here is what I wrote:
On how evolution could be fast enough to get things like us, one distinction worth mentioning is that one can be confident that X is the mechanism underlying some phenomenon B, without being clear about how exactly X in fact manages to do B.
An an example, consider the case where X is the brain and where B is our thinking. We are sure that the brain is the mechanism underlying our thinking, but we are still very mystified at how the brain can really engender all this thinking and experiencing we do.
In this light, now let X be evolution and B be the speed at which it can create fancy things like us. Just as we're sure the brain underlies thinking, we can be sure that the (ugly, sloppy, lengthy) mechanism of evolution underlies the complex biological stuff we find on Earth. And despite being overwhelmingly convinced that this is the case, we can still be thrown for a loop as to how natural selection can do it in the time frames allowed.
I don't mean to suggest that we don't know a lot about how the mechanism of natural selection leads to the biology. We do know a lot. And we also know a lot about how the brain leads to our mental life. But in each case there are still huge tracts of unanswered questions. (I'm on the pessimistic side, actually; I believe we're millennia away from understanding the brain and genes.)
For evolution, knowing the genome is only the first step. It may be hundreds of years or more before they can comprehend how it works together in a unified computational fashion. And with that understanding, they may better appreciate that the range of possible offspring is much much lower -- and the survivability and functionality much much higher -- than one would expect if genes were only flipping at the individual level.
The general point is that figuring out “that X is the mechanism for B” is a radically simpler problem than figuring out “how X works as a mechanism for B.” This is so obvious, and yet easy to overlook. For example, it doesn’t take a rocket scientist to conclude that my computer is the mechanism that allows these letters I’m now typing to appear before me. But it does take a rocket (or computer) scientist to understand how my computer manages to make this happen. Showing that evolution is the mechanism of life has an astronomically lower bar than showing how evolution exactly does it.
What was unexpected about my response was my admission that we don’t completely understand how evolution can be fast enough. The reason this is unexpected is that we scientists are often unwilling to show any traces of uncertainty about evolution to intelligent-design folks, probably out of a fear that it “may only encourage them.” But we are, in fact, uncertain about some aspects, and if we claim otherwise and get called out, our credibility will be blown.
Instead, we scientists should be glad to display uncertainty about evolution. …but only in regards to how exactly it works in detail to achieve the complexity found on Earth. We should reserve our claims of certainty to where we truly have them, namely in the claim that evolution is the mechanism underlying life on Earth. …and we should emphasize that the bar for showing this is vastly lower than for showing how.