Essential reading for evo supporters.
The Evolutionary Accessibility of New Enzyme Functions: A Case Study from the Biotin Pathway
ā¦This leads Koonin and Wolf
to reject convergent evolution (extensive similarity appearing
by evolution from dissimilar starting points) as implausible.
But from this they conclude that homology, while not
formally proven by similarity, is nonetheless overwhelmingly
supported in cases where chance convergence is implausible.
The problem with this is that all non-chance alternatives
must be considered once chance is ruled out. Yet Koonin and
Wolf consider only one of these alternativesāthe standard
Darwinian one.
We agree with their rejection of chance, but we argue here
that the Darwinian explanation also appears to be inadequate.
Its deficiencies become evident when the focus moves from
similarities to dissimilarities, and in particular to functionally
important dissimilaritiesāto innovations. The extent to which
Darwinian evolution can explain enzymatic innovation seems,
on careful inspection, to be very limited. Large-scale innovations
that result in new protein folds appear to be well outside
its range [5]. This paper argues that at least some small-scale
innovations may also be beyond its reach. If studies of this
kind continue to imply that this is typical rather than exceptional,
then answers to the most interesting origins questions
will probably remain elusive until the full range of explanatory
alternatives is considered.
When Theory and Experiment Collide
ā¦As other scientists have found with other enzymes, it turned out
not to be a snap. The technical details are reported in a paper just published in
BIO-Complexity. [2] Here weāll keep it simple.
Based on our experimental observations and on calculations we made using a published population model [3], we estimated that Darwinās mechanism would need a truly staggering amount of timeāa trillion trillion years or moreāto accomplish the seemingly subtle change in enzyme function that we studied.
Now, if I were a Darwinist a result like this would bother me. Iām sure some of my fellow Darwinists would try to dismiss it as irrelevantā¦ but that would bother me all the more.
The excuse for shrugging it off would, I expect, be that the transition we examined isnāt actually one that anyone thinks occurred in the history of life. Thatās true, but it badly misses the point. As Ann and I made clear in the paper, our aim wasnāt to replicate a historical transition, but rather to identify what
ought to be a relatively easy transition and find out how hard or easy it really is. We put it this way in the paper [2]:
Whether or not a particular conversion ever occurred as a paralogous innovation (or the direction in which it occurred if it did) is not the point of interest here. Rather, the point is to identify the kind of functional innovation that ought to be among the most feasible ā¦] and then to assess how feasible this innovation is.
So, if I had a Darwinist alter ego, hereās the problem heād be facing right now. To dismiss our study as irrelevant, heād have to say (in effect) that he sees no inconsistency between these two assessments of the power of Darwinās mechanism:
http://biologicinstitute.org/wp-content/uploads/2011/04/transitions.jpg
But thatās not an easy thing to say with a straight face, is it?
Having always believed the bottom picture to be correct, my alter ego would be very reluctant to reject it. And yet he wouldnāt be able to deny the obvious. There is in fact a jaw-dropping, ludicrous, even
grotesque inconsistency between the top picture and the bottom picture. They canāt
possibly both be true. But that realization, of course, forces an uncomfortable decision.
And here I must confess to feeling more than a little sympathy for my alter ego. I think itās because of what we have in common.
He loves science.
So do I.
He loves stories.
So do I.
He sees a role for stories in framing scientific ideas.
So do I.
And he has said to himself, āThe progress of science has invalidated my alter egoās favorite story.ā
So have I.
