I just finished re-reading Simon Conway Morris' article, Evolution: Bringing Molecules into the Fold (Cell 100: 1-11, 2000). Morris makes many arguments that fit nicely into my developing views concerning front-loading evolution. In fact, the article is so good that I will discuss it at length.

Morris argues that our understanding of evolutionary processes and its mechanisms are fundamentally incomplete (that is, we are not simply missing mere details). I could not agree more, and in fact, recently offered the following comments in my discussion of junk DNA:

The non-teleological view of evolution is that it is not really a biological process, but instead is the consequence of many smaller biological processes. Or look at it this way: the purpose of life is not to evolve; it just happens. But a teleological view of evolution likens it to a biotic process (roughly analogous to ontogeny). Evolution was intended/anticipated. I suspect much of the so-called junk DNA comes into play here. Is evolution really nothing more than a by-product of messy molecular interactions or is it far more sophisticated (itself being designed)? Concerning the cell and its contents, Bruce Alberts noted, " But, as it turns out, we can walk and we can talk because the chemistry that makes life possible is much more elaborate and sophisticated than anything we students had ever considered. " More and more, I am coming to seriously think that in another few decades, another leading scientist will write, " But, as it turns out, we exist because evolution has been much more elaborate and sophisticated than anything we students had ever considered. "

Morris begins his article by pondering the meaning behind that fact that "deep and pervasive similarities amongst the metazoans seem to be the rule." There is something more here than mere evolution. He first considers sponges, generally accepted as the most "primitive" form of metazoan life:

their biochemistry includes elements that seem to foreshadow the immune system of vertebrates. Sponges do not have nerve cells, but paradoxically they possess neuronal-like receptors....With such features, sponges seem to be almost "animals in waiting": everything is in place but nothing happens.

Morris adds that this is, however, a distorted views for two reasons. First, much happens with sponges; they just exist as sponges and not "animals." Secondly, "the basic building blocks and processes found in metazoans are very widespread among eukaryotes and must have originated much earlier than the first animals."

Elsewhere, Morris drives this point home as follows:

the diversity of life is, in molecular terms, little more than skin deep. Most, perhaps all, of the basic building blocks necessary for organismal complexity were available long before the emergence of multicellularity.

Observations like these constitute good evidence of front-loading. What this means is that all the hardware needed to form all the various metazoan life forms already existed in unicellular organisms. While this may be commonly seen merely as evidence for common descent, a bigger picture emerges from a deeper look.

(1.) First, it would appear more and more that a designer could design mutlicellular life through unicellular life forms. This is front-loading.

(2.) Secondly, our perception of evolution has been skewed over the last century. This is not surprising, as science is limited by the perceptions its tools can deliver. Yet how has the perception been skewed? From a morphological and behavioral perspective, life is immensely diverse. But the molecular perspective shows such diversity to be "skin-deep." Thus evolution, as evidenced by the fossil record, has not been about developing novel hardware to solve adaptive problems. It has been more about reshuffling, testing, and deploying the molecular endowments it has been given. Put bluntly, all the evolution contained in the entire fossil record and inferred by our phylogenetic trees has been largely a footnote in the development of life. The really interesting and important questions concern the origin of this "animal in waiting" hardware that was infused into protozoan life forms.

(3.) Thirdly, one can always attribute the origin of such hardware to non-teleological processes, but what a coincidence all this would be. That is, selective pressures shaping protozoan life forms for millions of years just happened to find solutions that would just happen to become essential for metazoan life.

Returning to Morris, he introduces a concept called molecular inherency that he defines as "a gene known to be of major importance in organogenesis in a higher animal also occurs in a more primitive group." This is very similar to one way in which I infer front loading.[1] Morris lists a few examples:

a. Sponges contain equivalents to many Pax genes.

b. Otx is a gene family important in the development of the brain/head of arthropods and vertebrates. But it is also found in Hydra (cnidaria), where it plays only a role in cell movements.

c. Genetic and tissue studies of Amphioxus show a "vertebrate in waiting."

Again, all of this speaks to front-loading. For example, if one wanted to design a vertebrate, they would not need to design vertebrates. They need only design Amphioxus and evolution is then rigged to evolve vertebrates.

Cooption and Constraint

Morris also speaks of cooption. Front-loading, or genomic inherency, lead us to expect cooption. After all, it is cooption that exploits and draws out the potential of the front-loaded state. It seems (at least to me) that Morris is hinting that the phenomena of cooption is not an evolutionary "free-for-all" but instead occurs under high-order constraints. For example, Morris quotes Davidson and Ruvkun who "gently question received orthodoxy by reminding us that cooption of genes might be analogous to plugging of particular computer "chips" into a new program." The program is not the product of cooption, it is what is designed to make use of cooption. Yet as Morris notes, the "how, why and when cooption occurs is, however, only now beginning to be explored."

A further word on cooption. I have expressed skepticism concerning the notion that this phenomena explains the origin of IC molecular machines. However, that cooption may not be a good explanation for the origin of IC molecular machines does not mean that is was not involved in helping to generate the diversity of morphological forms that followed from the front-loaded state(s). That is, if cooption is played out on the stage set up by front-loading (which is maintained, at least in part, by the interplay of molecular machines), trying to use cooption to explain the make-up of the stage is like putting the horse before the cart.

Morris touches on the significance of the discordance between genotype and phenotype. He explains, "a much more interesting problem [is one] that questions whether genetic similarity, however striking, can be equated in any simple fashion with a shared ancestry." He then provides a very provoking quote from Nagy:

Should vertebrate and insect limbs be considered homologous because they are patterned by similar gene networks? Or is the similarity an example of molecular convergence, representing not an extreme conservation of limb construction throughout metazoa, but merely a consequence of a limited number of molecular tools an organism has available to change its form?"

As a rule, evolution is not going to design new molecular tools. It is merely going to make use of the tools it has been given. This is front-loading. And this also points us to the design of evolutionary mechanisms.

Morris also brings up sea urchin development that may contain an important clue:

may have wildly different ontogenetic trajectories, with fertilized eggs developing into very different types of embryo that subsequently converge on similar adult forms.

and

Multiple genomic pathways in ontogeny are probably the rule, but in our present state of knowledge, this seems rather surprising given that once a particular pathway is established, the advantages of altering it, when the end-product remains unchanged, are obscure.

Thus, here we have an example that demonstrates there can be multiple pathways to a very similar endpoint in ontogeny. If evolution is a biological process, rather than merely a consequence of many smaller biological processes, why can't we extrapolate this to phylogeny? And thus, the whole phenomena of 'convergent evolution' comes into play. Is this yet another clue to front-loading and the design of evolution? After all, convergence is, by definition, similarities not reflecting a common ancestral state.

Morris writes:

The question we need to ask is whether a structure (molecular or organismal) is similar because it shares a common ancestry and thus is homologous or because there is no (or very few) alternative. The former approach, of course, underpins most evolutionary thinking and has potentially a strong historical component. Convergence, on the other hand, points towards adaptive constraint in which the historical dimension is relatively unimportant.

The concept of adaptive constraint is another reminder that evolution is not an adaptive free-for-all. Evolution is constrained by the very substrate upon which it is played out. Thus, it is the substrate of evolution, and not evolution itself, that is of primary importance in these origin disputes. Morris then cites some very interesting examples of convergence which show that "remarkably similar endpoints can be arrived at from quite different starting points." I'll come back to these in a follow-up.

Let me finished with a provocative quote from Morris:

Just as phenotypic diversity of life excites the imagination of the naturalist, so the range of molecules and the sophistication of their biochemistries impress the molecular biologist. In comparison, the underlying constraints on form and the inevitability of convergences have received less emphasis. Why should this be so? There seems to be two reasons. The first is that if evolution is in some sense channeled, then this reopens the controversial prospect of teleology; that is, the process is underpinned by a purpose.

Let me merely say that we have just begun to understand evolution and I think we will one day find that the processes of evolution are far too sophisticated to fit comfortably in the Modern Synthesis. Darwin helped us to understand things like finch beaks and the spread of antibiotic resistance. His concept has been extrapolated to all other origin events merely because we don't understand evolution very well and have no better explanation. Those days are changing.