May 16, 2020 | David F. Coppedge

Natural Selection Is Catnip to Darwinians

The words put them in a state of euphoria, dreaming they have explained something when all they have said is “stuff happens.”

Researchers discover the evolutionary origins of the cat attractant nepetalactone (Max Planck Institute for Chemical Ecology). In her trance, Sarah O’Connor of MPI imagined that genes for the synthesis of nepetalactone (the iridoid that causes a reaction in cats) devolved in some mint ancestor, then evolved back again.

They were able to determine the mechanisms for the loss and subsequent re-evolution of iridoid biosynthesis in catmint. These new discoveries provide broader lessons in the evolution of plant metabolic novelty and diversity….

“This can in turn help us to uncover the selective pressures that led to loss and regain of this pathway” [O’Connor says]…. She wants to understand how and why plants apply such complex chemical reactions to produce this fascinating diversity of molecules: “Plants are constantly evolving new chemistry. With our research, we would like to get snapshots of this evolution in action.”

Darwin cat in ecstasy, hugging natural selection

The paper in Science Advances, “The evolutionary origins of the cat attractant nepetalactone in catnip,” with 17 authors, goes into a lot of detail of which plants have this compound and which don’t. Presumably it didn’t “evolve” to titillate cats, but to resist herbivorous insects. Interestingly, the Biblical plant hyssop doesn’t have it, nor do many other similar plants. Nepeta (catnip) sits off by itself as a producer of nepetalactone, with more genetically distant plants. The authors try to fit the pieces together with stories of gene duplication and sub-functionalization, but in the end rhapsodize with visions of futureware while waving the magic wand of natural selection:

Overall, these ancestral reconstructions and positive selection analyses support the model of a gene duplication of a PRISE ancestor with minor ISY side activity, followed by selective pressure to form a dedicated iridoid biosynthetic enzyme. While this hypothesis fits a standard model of enzyme evolution through duplication of promiscuous ancestors, we acknowledge that further work is required to unravel the molecular basis for this transition.

Later, they fall under the power of suggestion:

This proposed chronology suggests that gene clusters are not the cradle of plant metabolic novelty but may instead emerge subsequent to enzyme evolution while the nascent metabolism is under strong positive selection. This study highlights the complementarity of enzyme and genome evolution in elucidating the emergence of novel chemistry in plants.

The measure of “positive selection,” however, is defined as a ratio of non-synonymous mutations to synonymous mutations, which is only an indirect proxy that requires interpretation about what it implies. But surely the more interesting question is how a plant learned to synthesize complex molecules by chance in the first place; “the crucial innovation required for nepetalactone biosynthesis was the NEPS enzymes, which act in partnership with ISY to control the profile of stereoisomers formed from the cyclization reaction.” But those enzymes already existed! If the environment could create them by “selective pressure”, then every plant in the vicinity would make catnip vapor.

The evolution of nepetalactone biosynthesis in Nepeta is not simply a re-emergence of iridoid biosynthesis in this lineage; it also represents an evolutionary innovation. Nepetalactone is an example of repeated evolution with a twist; while nepetalactones maintain the iridoid structure, there are key differences compared to other iridoids found in the mint family.

It’s easier to lose an enzyme than to make one. They already believe gene loss was involved in many of the species that don’t make nepetalactone. Why not stick to gene loss as the cause of the observations? Why do they force the narrative into a story of “re-emergence” of an “innovation” involving biochemical wizardry? The answer is that their Darwinian phylogeny requires it. Things must evolve in a Darwinian sequence from simple to complex rather than devolve in a degenerating world. To make it work, they sniff their catnip and, when sufficiently intoxicated, wave the magic wand of natural selection to bring about whatever miracles are required.

Short Examples

Fossil record analysis hints at evolutionary origins of insects’ structural colours (YaleNUS College, Singapore). Darwinians just cannot think outside the box of evolution and long periods of time.

The fact that very similar substrate-matching green colours have been maintained over hundreds of thousands of generations suggest that the same selective pressures for camouflage have been acting on these weevils. This is consistent with a recent study by Asst Prof Saranathan and weevil systematist Dr Ainsley Seago that suggests the weevils’ colours evolved initially for camouflage amongst their leafy background, before diversifying for other functions such as to signal potential mates or deter predators.

But what if it wasn’t hundreds of thousands of generations? What if they originated with structural color? How did they “evolve initially” by chance? How many mutations did that take to invent genes that could tailor feather nano-structures able to intensify light?

Ancient aquatic crocs evolved, enlarged to avoid freezing (University of Nebraska-Lincoln). This one’s a crock, all right. Natural selection causes change, except when it causes stasis. Selection is the great molder of body forms. Believe.

Though their maximum size remained almost constant, marine species did evolve two to three times faster than the semi-aquatic and terrestrial groups, Gearty found. Along with increasing the size of smaller aquatic species, natural selection molded body forms to surmount the challenges presented by water. Scales, plates and other drag-increasing skin deposits disappeared. Heads and tails flattened. Snouts narrowed.

Natural selection: better than sex. This tom looks fully intoxicated.

Sexual reproduction: sometimes it’s just not worth the effort, study finds (Monash University). The euphoria of evolutionary catnip lasts longer and reaches higher when Darwin Flubber is applied to the shoes. With a higher perspective, an evolutionist can see natural selection as an efficiency expert.

This phenomenon, called ‘parallel evolution’, suggests that sexual populations were better at keeping beneficial mutations, and discarding deleterious mutations, than asexual populations . “This finding provides support for one of the theoretical explanations for why sex is beneficial: sex and recombination makes natural selection more efficient,” Dr McDonald said.

Did old McDonald name any beneficial mutations? No. But under the influence, he can imagine they must have been there. “Most mutations are deleterious or have no effect, however some mutations may be beneficial,” he says, ignoring genetic entropy. Sometimes it’s just not worth the effort to do science the old fashioned way, by demonstration instead of speculation.

Footprints of natural selection at the mannose-6-phosphate isomerase locus in barnacles (PNAS). When you look at one gene in one genus, does the picture of natural selection get clearer? This paper uses the word “selection” a whopping 93 times. The authors are overdosing on evolutionary catnip! There’s balancing selection here, purifying selection, heterogeneous selection and fill-in-the-blank selection in their analysis of a particular gene from barnacles. But is there any clear indication that natural selection leads to increased fitness or adaptive innovation? None! Look at these typical quotes showing squishy conclusions like ‘on the one hand this, on the other hand, that, but more work is needed.’

As such, the magnitude and direction of zonation at Mpi may emerge from the antagonism (or synergism) of these temporally and spatially varying selective pressures across different life stages. Overall, there is little doubt that Mpi is experiencing a complex landscape of selection, but a model of selection focused on a single site (e.g., Q390K) and one single stress gradient (e.g., temperature) is too simplistic to account for the molecular evolution of the locus…..

This spatial–temporal variation in Mpi zonation is the primary evidence that the gene experiences heterogeneous selection. As such, we propose that genetic variation at the locus is maintained by a complex landscape of natural selection in which long term balancing selection cooccurs with recent instances of allelic replacement. Although more work is necessary to fully resolve Mpi’s connection to fitness, our results provide a robust example regarding the roles and spatial scales of adaptive responses in a natural population evolving in a highly heterogeneous environment.

In short, they don’t know which way selection is going, whether it is positive, negative or neutral, or whether it works differently at different life stages, or whether any of it is related to fitness! No innovation or novel structure is reported. But they know that natural selection has something to do with this mess, because Darwin and Eugenie Scott insist that Evolution is a fact!  Evolution is the one great truth that scientists most certainly know! It has to be true, because the alternative is unthinkable!

Darwin Party members deeply inhale the fumes of evolutionary catnip—natural selection—and go crazy, losing all restraint. They know they won’t get in trouble for being intoxicated on the job, because the Darwin Party Dictatorship of the Proletariat has legalized catnip while working. In fact, Party bosses encourage it; they pump the fumes out with their fogma machines to get the proletarians hooked on it. The fumes liberate the imagination and increase the vividness of their visions, where tangled webs of hair going in all directions conjure up visions of the hoary face of—blessed be he—the Bearded Buddha.




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