Darwin Imagineers Stuff Fantasy Narratives with Irrelevant Details
Brains are like trees, only ours are upside down because plant brains are in the roots. Both came from chemicals.
Where did brains come from? (John Hewitt, Phys.org). John Hewitt speaks of “pre-genetic Darwin imagineers” – his term, not ours. It implies that post-genetic Darwin imagineers are still at work, only that they have more sophisticated ignorance now.
In Hewitt’s visit to evolution’s Magic Kingdom, he is intrigued to see brains emerging from neurons that emerged from secretory cells in snails that emerged from signaling molecules in sea urchins. He traces a seamless line through these widely scattered points as if a human brain is a natural (indeed, inevitable) consequence of upwardly-evolving molecules and cells wishing to improve their lot in life.
He begins by claiming that a human is very much like a plant, except that a plant’s brain is in its roots that point down, where our brains are in our heads that point up. The first graphic shows a human figure planted upside down next to a tree.
Guess what name will start off Hewitt’s imagination fest:
Charles Darwin wrote a book called “The Power of Movement in Plants” with his son Francis in which they first identified the root apex as the central command center of plants. In contrast to our own orientation with respect to Earth’s gravitational field, Darwin proposed that the root apices represented the anterior cognitive pole of the plant or tree, while the shoot apices represented the posterior pole. In this view, the root apices are solely responsible for identifying and targeting nutrient-rich and toxin-depleted areas of soil in which to grow, while the shoots generate the sexual apparatus for reproduction.
Another informative brain/plant comparison can be made between the highly polarized cortex and trees. Pyramidal cells extend highly fractalized apical dendrites up into the cortical sheet while puncturing the white matter below with a deeply penetrating and purposively ramified axon. To understand why trees, nervous systems or individual neurons concentrate resources in certain regions within themselves and proliferate uniquely branched elaborations into different external environments, we need to identify the chemical partners and physical persuasions each seeks and responds to.
Hewitt is reviewing articles in a special edition of the Philosophical Transactions of the Royal Society. He seems mesmerized by display after display of imagination, visualizing chemical brains and hopeful molecules. This is all very intriguing, he says. The Magic Castle always advertises a good ride. The sign over the entrance says, ‘All things evolutionary are possible to those who wish upon a star.’
Jékely’s chemical brain hypothesis postulates that neurotransmitters came before synapses and neurites, as opposed to the other way around. In other words, transmitters make nervous systems. He further suggests that the evolution of circulatory systems and neurohaemal organs released the constraints imposed on peptidergic signaling by diffusion. The so-called hemocoelar circulation within the primary body cavity of invertebrates, coupled with peptide release, ensured the rapid conduction of signals throughout an increasingly large body. While intriguing, it is also true that primitive nervous systems, which predate modern circulatory systems (with oxygenating and immune cells), also distribute nutrients and metabolites, and may have originally evolved for this purpose.
Wait; nothing evolves for a purpose. Hewitt forgets that Darwinism is blind, aimless and purposeless. But we mustn’t disturb Hewitt’s trance as he follows the narrative being piped through the magic castle’s PA system. He approaches the blinding light of evolution’s powerhouse, natural selection:
In this case, the compelling narrative is that peptide or small protein neurotransmitters must have evolved first. The genetic record indicates that secreted proteolytic digestive enzymes and peptide toxins with readily adaptable, three-dimensional structures were the early molecular targets on which natural selection productively operated.
Note: To understand Hewitt’s article, one must pass over the Jargonwocky elements that distract from the story. Statements like “Cleavages frequently occur at di- or monobasic sites (like lysine-arginine) by prohormone convertases followed by C-terminal α-amidation where a bifunctional peptidylglycine α-amidating monooxygenase (PAM) enzyme converts a C-terminal glycine into an amide” have nothing to do with the narrative that Hewitt is pursuing. They are only props to give a feeling of science awe to the target of the presentation, which is: “Where did brains come from? Chemicals.” In fact, the above jargon-loaded sentence discusses present-day complex processes in cells – not evolution. Astute readers are forewarned.
Wandering on, Hewitt admires another imagineered exhibit:
In a later article, Detlev Arendt observes that as multicellular animals emerged within a world of host-associated and likely symbiotic microbiota, organisms could have evolved neural phenotypes as immune mediators discriminating self from nonself within their enteric cavities.
Next, Hewitt kneels in awe at the ancestor that gave rise to his brain:
These giant, paired, serotonin-containing interneurons are involved in feeding arousal, and their descendants can be recognized across all Euthyneura (basically snails and slugs). It is a level of molluscan subclasses separated by more than 380 million years of evolution in each direction and therefore of immense importance in understanding early nervous systems.
King Charles reappears as the sovereign conferring knighthood on his loyal molecules.
…. L. Moroz et al. trace the origins of the most primitive nervous systems to discover how a select few of the thousands of ordinary molecules under cellular control were ultimately knighted into neurotransmitters. While many of the ideas presented in this paper, as well as the larger issue on origins of brains, are still hypothetical, truth is often most readily accepted when transmitted in surprise. Therefore, the unlikely yet inevitable emergence of nervous systems through the simple requirements of extracellular digestion in evolving multicellular forms is an idea that can be readily swallowed once the appropriate chemical links are laid bare.
Now, at last, humans can understand how their primitive brains drive them to the refrigerator. Brains did not emerge for thinking. They emerged for eating. Surprise! Ain’t that the truth? Better swallow it, because there’s nothing else in the Darwin kitchen.
As the “which came first” story for transmitters and receptors is now rapidly unfolding, the once mysterious origins of nervous systems that puzzled pre-genetic Darwin imagineers now becomes obvious.
Eat your Darwin swill like a good apprentice. You will like it.
Fortunately there is good intelligently-designed food outside the Darwin castle in the sunlight. One can toss out everything Hewitt and his fellow imagineers say. If their brains emerged by chemical natural selection, nothing they believe can possibly be true, including the notion that their brains emerged by chemical natural selection. For the rest of us, this episode provides comic relief. It’s funny how seriously these imagineers take themselves. They actually believe their made-up narratives. Turn on the lights and it all gets exposed as Darwin’s fantasyland theater of the absurd.