I’m surprised at how quickly Darwinists have abandoned any claim that evolution is a powerful process at work today, retreating to the position that its power is a thing of the past. The convenience of that stance, of course, is that it enables them to insist that natural selection was a powerful mechanism without committing themselves to the more risky proposition that it still is.
Laurence Moran is among those who seem to favor this approach, at least as I interpret his recent post.
Ann Gauger and I have shown that Darwin’s mechanism cannot accomplish what appears to be one of the more favorable functional transitions among proteins. Specifically, we’ve presented experimental evidence that the protein pictured here on the left cannot evolve to perform the function of the protein shown on the right, despite their striking similarity and the generous assumptions we granted.
We completely agree with Moran that this exact transition never happened in the history of enzyme evolution (and said as much in our paper). But evidently we expect more of Darwin’s theory than he does. In particular, we expect it to conform to the established norm of offering universal principles instead of just-so stories.
If it can be shown that natural selection actually has (present tense) the creative capacity attributed to it, then I will certainly join those who are calling everyone to accept this. But if the facts go the other way, as it seems they have, then perhaps the reality check should likewise go the other way.
Darwin certainly didn’t make the mistake of relegating natural selection to the past:
It may metaphorically be said that natural selection is daily and hourly scrutinising, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.
By this classically Darwinian view, all that was needed for our ape ancestors to evolve the intellectual capabilities that distinguish us so dramatically from apes was the right “conditions of life.” It follows that any ape population of today, if placed in those conditions, should evolve in the same way — not becoming human per se, but rather human-like in every respect that we benefit from being un-ape-like. And similarly, all it should take for one member of a protein family to transition to a new function is the right selective environment.
As old-fashioned as this classical view sounds in a day when very few biologists are proudly waving the flag of natural selection, it did at least have its place in the time-honored scientific tradition of making claims that can be tested today.
So, to Moran I say, regale us with heroic stories of magically evolvable apes and magically evolvable enzymes if you must, but when you’re finished with the stories, be sure to join us in doing the science that should convince everyone one way or the other as to their plausibility.
It’s the same challenge I put to James Shapiro at the beginning of the year:
We can go into the lab and modify bacterial cells by deleting the entire set of genes dedicated to the synthesis of tryptophan, one of the essential building blocks of proteins. When we observe what happens when these modified cells are given just enough tryptophan to grow and reproduce, we will see lots of things happening, but none that can be expected to reinvent a set of genes for making tryptophan, even in a large population over billions of years.
I know of many processes that people talk about as though they can do the job of inventing new proteins (and of many papers that have resulted from such talk), but when these ideas are pushed to the point of demonstration, they all seem to retreat into the realm of the theoretical. Having followed this debate for some time now, and having made several experimental contributions to it, Ann and I have become convinced that none of the current naturalistic ideas about the origin of protein folds or the functional diversification of existing folds actually works in any general sense.
But of course, as experimentalists we are very willing to see the evidence that might prove us wrong.
Image credit: sameold2010/Flickr.