“Notions” About Metamorphosis Fall Short of Scientific Explanations
The authors of a new paper on insect metamorphosis admit that its evolution is “poorly understood,” adding that “why this extreme lifestyle evolved is unclear.” Stated succinctly, they don’t know how it evolved; they don’t know why it evolved; they just know that it did evolve. With non-Darwinian explanations ruled out from the starting gate by the philosophical rule of methodological naturalism, what’s a Darwinian to do? Some of them came up with a notion.
Our work supports the notion that the holometabolous life history evolved to remove developmental constraints on fast growth, primarily under high mortality.
Dictionary.com gives five definitions for “notion”—
a general understanding; vague or imperfect conception or idea of something: a notion of how something should be done.
an opinion, view, or belief: That’s his notion, not mine.
conception or idea: his notion of democracy.
a fanciful or foolish idea; whim: She had a notion to swim in the winter.
an ingenious article, device, or contrivance; knickknack.
Science aspired to rise high above notions. For instance, in Leeuwenhoek’s day, people believed in spontaneous generation. The citizen scientist debunked that notion using the tools of observation, testing, and causal explanation. He observed the complete life cycle of ants, fleas, mussels, eels, and various insects, proving that all organisms had parents.
Notions have no place in scientific explanation. They may serve a pre-scientific purpose by suggesting a hypothesis to be tested but fall short of the demands of rigorous science. Notions (“small items displayed for sale”) belong in department stores, not universities.
Terms in Metamorphosis Science
Insect metamorphosis is best illustrated by the butterfly hatching from a chrysalis. This form of complete metamorphosis, in which the larval body plan is broken down and a new adult body plan is built, is called holometaboly. An adult butterfly hatches from its straitjacket with new wings, new limbs, a new proboscis, new sense organs, new reproductive organs, a new digestive system — a whole new organism built from the same genome.
In its documentary Metamorphosis: The Beauty and Design of Butterflies, Illustra Media compared the transformation of a caterpillar into a butterfly to a Model T driving into a garage and emerging as a helicopter, ready to fly, having been constructed out of all the disassembled parts of the car (see excerpt here). It’s no wonder that this kind of metamorphosis is “poorly understood” by Darwinians. Strictly speaking, holometaboly includes four stages in the life cycle of insects that undergo complete metamorphosis: egg, pupa, larva, and adult (also known as the imago). Over 50 percent of insects undergo holometaboly.
There’s a simpler form of metamorphosis known as hemimetaboly (incomplete metamorphosis) that might give a creative storyteller a steppingstone for support of his notion. This kind of life cycle, exemplified by grasshoppers, dragonflies, lice and many others, skips the pupa stage and goes from egg to nymph to imago. A few other insect orders are ametabolous(exhibiting slight or absent metamorphosis), growing in size from birth to adult. Only “primitive” wingless insects are ametabolous. Is there an evolutionary progression evident in these life cycles? That wasn’t clear to the authors of a new paper:
Holometaboly has fascinated students of natural history since Aristotle, yet the evolution of this extreme form of metamorphosis is puzzling: If decoupling different life stages is the key adaptation of metamorphosis, simpler forms of metamorphosis such as hemimetaboly should suffice. What is then the extra driver for the evolutionof complete metamorphosis?
The Notion Marketers
Four evolutionists from the Free University of Berlin and from Princeton published their notion in the Proceedings of the National Academy of Sciences. In the Significance statement of their paper titled, “Rapid growth and the evolution of complete metamorphosis in insects,” Manthey et al. boasted of the explanatory power of their notion.
More than half of all animal species are insects that undergo a dramatic rebuilding of their bodies, dubbed complete metamorphosis, as exemplified by the transition from a caterpillar through a pupa to a butterfly. Why this extreme lifestyle evolved is unclear. Here, by combining empirical data and mathematical modeling, we find that the holometabolous insects grow much faster than insects that do not show this extreme form of metamorphosis. This allows to first grow and then build the adult body, allowing for much faster growth.Fast growth is favorable under many ecological conditions such as competition and predation. This growth advantage reported here can almost certainly help to understand the huge diversification of the holometabolous insects.
The Abstract mentions the “notion” quoted earlier. But they didn’t leave it at the notion stage, a Darwinian might object. They tested the notion with empirical data and mathematical modeling, didn’t they? Well, let’s see.
The “Mother-May-I” Allow Notion
The essence of their notion is that complete metamorphosis allows the insect “to first grow and then build the adult body, allowing for much faster growth.” Stop right there! Are we to picture the magic hand of evolution, like a fairy godmother, granting permission to evolve? Does she tell the caterpillar entering a chrysalis, “You are now allowed, child, to build your adult butterfly body faster than you could before.” How does this make their explanation superior to a notion? Continuing this mini-fable, wouldn’t the caterpillar complain to the fairy godmother, “But how am I supposed to do that? I know how to die, dissolving all my existing parts, but where are the instructions for building wings and a proboscis and everything out of the debris? This chrysalis you gave me looks like a casket! How do I know I will get out the other side alive, let alone fly?”
In the Illustra film, this argument is stated more elegantly by Paul Nelson and Ann Gauger (see my earlier articles here and here). Unless there is a plan and a genetic program already in place to emerge from the chrysalis with wings and antennae and all the new body parts, the caterpillar, like the melted down Model T, is the end of the line. One cannot assume that “allowing” it to happen will make it happen. Yet Manthey et al. continue to use the Allow Notion:
Metamorphosis, the life-cycle discontinuity between larval and adult phenotypes, is found in the majority of animal taxa and is commonly explained as an adaptation that allows organisms to optimize their phenotypes to different habitats or diets.
A synonym for “allowing” is “enabling” good things to happen. Enable, like allow, personifies selection as a beneficent driver. They disguise this driver by embedding it in a mathematical model. This is evident in the following quote, where we notice they substitute “idea” for “notion” — the same fallacy.
We find that holometabolous insects have higher growth rates than hemimetabolous insects. This is consistent with the fastest reported growth rates in insects being reported for black soldier flies and burying beetles, both of which are holometabolous. Our mathematical model shows that in the presence of a trade-off between growth and differentiation, selection for fast growth results in the temporal decoupling of growth and differentiation and can result in the evolution of holometaboly. This effect is exacerbated under increasing risk of mortality.
Risk of mortality — recall the poor caterpillar worried about dying in the casket. Here comes the “enable” word; evolution will enable the caterpillar to come out alive as a butterfly.
Taken together, our findings are highly consistent with the idea that holometaboly enables insects to escape the developmental constraints imposed by a trade-off between growth and differentiation.
Twice they say their notions are “consistent with” some evidence. Correlation is not causation. Despite the whiz-bang math in their model, a model built with a notion confers no empirical adequacy on it. This is especially true when the model personifies the cause, contrary to the authors’ naturalistic worldview.
The “It Could Be Beneficial” Notion
A common flaw in evolutionary explanations is the assumption that a new trait or innovation might be beneficial. That doesn’t work except in hindsight. Because Darwinism lacks foresight, pointing to benefits of a trait today begs the question that it evolved yesterday. Natural selection cannot select what isn’t there. From the ancestor’s view before the innovation emerges, benefits can only arise by sheer dumb luck. It cannot say, “If I get this mutation, I will enjoy a benefit.”
How complete metamorphosis is related to the evolutionary success of the holometabolous insects, measured in terms of both species richness and habitat dominance, is poorly understood. One explanation is that once complete metamorphosis had evolved, the resulting higher modularity would enable higher evolvability, as for example shown by the high diversity of mouthparts in holometabolous insects. If, as we propose here, the decoupling of growth and differentiation has been the main driver for the evolution of complete metamorphosis, then any ecological situation where fast growth is beneficial would give holometabolous insects a significant competitive advantage over other organisms that display alternative forms of metamorphosis or no metamorphosis at all. The breaking of constraints on growth almost certainly provides an added evolutionary benefit to the other potential advantages provided by biphasic metamorphic life cycles.
Natural selection knows nothing of “potential advantages” that might accrue. Nothing in nature “evolves to” reach a potentially advantageous goal. Postdicting causation by observing existing benefits begs the question of natural selection. Why not consider that the benefits were designed into the original coding?
The Promissory Notion
For a beneficial trait to persist, it must be coded in genes. The authors never link their notion to genetic mutations being naturally selected. That part of the explanation, they say, is a job for future research. All they speculate is that their notion “can” or might work.
Our results do not make a statement about the developmental pathways that result in a larval and pupal stage of holometabolous insects but rather identify how selection can result in decoupling growth and differentiation. Bringing together the developmental and the adaptive evolution perspective on complete metamorphosis will be an important future challenge. This should allow for understanding genetic changes and their order that were required to result in this key innovation of the pupa.
Other Darwinians, they just suggested, are now “allowed” to explain how the benefits got coded in the genes. Others — not them — will bring the coveted “understanding.” With this promissory note, they tossed the hot potato of turning their notion into an explanation to others! But readers of a scientific paper expect understanding now. If it’s just a notion that might be explained later by others, why publish it?
Summary
Notions are beneath the dignity of science. They can serve as heuristics that lead to science, but they fall short of scientific explanations. An untested notion dies in its chrysalis and won’t fly. Weak papers like this getting published in major journals is one result of censorship of critiques from outside the Darwin Party.
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