In a new paper in Biology Direct, University of Maryland biology researcher Arlin Stoltzfus takes a non-Darwinian view of the origin of much biological complexity (“Constructive neutral evolution: exploring evolutionary theory’s curious disconnect“). He observes that “much of contemporary evolutionary genetics departs from the conception of evolution underlying neo-Darwinism, resulting in a widening gap between what formal models allow, and what the prevailing view of the causes of evolution suggests.”
He opens his paper by marveling at the “baroque and apparently gratuitous complexity” we see in biology. In particular, he thinks that natural selection is incapable of producing some of this complexity, such as a process called “gene scrambling.” He describes it this way, using an example from the lifecycle of a group of protozoans:
Gene scrambling. In a post-mating ciliate cell, the micronucleus divides, and one daughter is converted into a new macronucleus as the old macronucleus degenerates. Processing to generate macronuclear genes includes removal of intervening segments and unscrambling of segmented genes. (diagram citations removed)
In other words, genes are spliced together from different parts of the genome to make entirely new genes and proteins. Gene scrambling relies on a molecular machine that Stoltzfus calls the “inordinately complex spliceosome.” If you think that sounds like an extremely complex process, you’re right. But there’s no need to label these processes as “nugatory,” as Stoltzfus calls them. Once the molecular machinery exists to un-scramble genes, then scrambling them isn’t a problem. The question ought to be, how did this highly complex scrambling/unscrambling machinery arise? Stoltzfuz thinks it’s too complex for Darwinian processes to explain:
It is hard to imagine an idea less congenial to the adaptationist habit of thought that has dominated biology from pre-evolutionary times. The classic paradigm of an evolutionary explanation is an adaptive rationale: feature X exists by virtue of benefit Y. If one version of “Y explains X” doesn’t work, the adaptationist imperative compels us to revise the rationale (Y’), or re-define the feature (X’), a cycle that may be repeated indefinitely.
So Stoltzfus rejects Darwinian explanations for these features. But he’s no proponent of intelligent design. Does his alternative explanation work? He calls it CNE or “constructive neutral evolution”:
CNE seems to provide something completely different: not features that are noisy, limited manifestations of an adaptive reason-for-being, but complex features that emerge by an internal dynamic without an adaptive raison d’�tre. Our neo-Darwinian intellectual ancestors — who derided the notion of internal forces as an appeal to vitalism — would have scoffed at CNE.
In other words, according to Stoltzfus, the ciliate’s ability to rewrite its genome exists for no apparent reason — it’s just an emergent property that came into existence by sheer chance. Is this convincing? Can chance events, unrelated to the need to survive and reproduce, explain the origin of highly complex structures and processes that allow an organism to survive and reproduce?
While gene scrambling is a highly complicated process that might seem to us OVER-complicated, it still works, and it allows these ciliates to survive and reproduce under their revised genomes. Complex features that adequately perform a function usually don’t just happen without a reason. Stoltzfus seems aware of this problem:
The ultimate cause of scrambling, in the CNE model, is not an adaptive rationale, but a dynamic in which a gratuitous unscrambling capacity opens the door for the system to wander into a morass of scrambled configurations. This tendency, which reflects an asymmetry in the space of possibilities, is present whether changes take place by drift or by selection.
Yet, our claim to have identified an intrinsic tendency is unsatisfying, because we have not implicated a proper mechanism. Evolution does not look ahead: for every effect, there must be a blind, local cause. The doctrine of mechanism demands that we identify such causes. To invoke, as a causal mechanism, a global asymmetry in a possibility-space — a mere abstraction about future potentialities — would be to leave the mechanistic imperative unanswered.
The lack of a properly construed cause for intrinsic tendencies is an issue with implications beyond CNE.
So CNE is supposedly a way of getting order for free — and no need to explain it because, under CNE’s own terms, we are freed from the obligation of providing any “properly construed cause.”
It’s nice to see that scientists increasingly recognize how Darwinian evolution fails to explain the data. But the post-Darwinian alternatives they offer, for the most part, don’t seem a whole lot more promising.
Update, 6/4/2013: Dr. Stoltzfus does go on to offer a “mutationist conception of evolution,” which deemphasizes the role of selection and claims that the cause of evolution is “bias in the introduction of variants.” But why should chance mutations be expected to generate anything advantageous (absent the guiding force of selection)? It’s difficult to see what any explanation for the origin of functional biological complexity is supposed to be.
Image: Oxytricha trifallax/Wikipedia.