Pre-Human Portals (Funnels, Bottlenecks): A Starter List
Let us now continue our discussion of the evolutionary development of hierarchical substrates (EDHS), this time focusing less on the substrate that emerges, and more on the portal (aka funnel, bottleneck), the converging gestational environment that appears to guide randomly created evolutionary assemblages, in the vicinity of the portal, toward the birth of the new, more developed substrate. Once we begin to see these portals, guiding certain kinds of evolutionary complexity, we open ourselves up to a powerful new way of understanding the world around us, and our place in it.
Portals are funnels that take some forms of evolutionary diversity out of a local environment, and lead with high probability to a more complex developmental state. They also act as bottlenecks, funnels, and gates through which the next leading developmental substrate must emerge. Finally, we can think of them like “wombs”, gestational environments for the next hierarchical acceleration that will invariably emerge. Just like the uterus and its developing embryo, portals bring together special systems which, in close spatiotemporal proximity, will lead to developmental emergence with high probability, even in complex, risky, and noisy environments.
While our math, physics, information theory, and simulation tools are often not yet up to the task of proving such portals, we can still use logic, argument, and cases of comparative and convergent evolution here on Earth to test any of our portal hypotheses.
Here are a few pre-human portals for your consideration. They are all colored in blue as we should expect them all to convergently and predictably emerge throughout our universe, as complexity builds, in a process of galactic development:
- Developmental physics, leading to the ubiquity of spiral galaxies (60% of galaxies in our universe), and Sol-type (G-class) suns (just 8% of our Milky Way galaxy’s stars, but right in the middle of the main sequence star distribution in luminosity and temperature on the Hertzsprung-Russell diagram, see picture right). Three other classes of suns (M, K, and F) have also been proposed as places where we might find long-term life-supporting conditions. Even when we account for the need for things like a moon, Astrobiologists now think there are tens to hundreds of millions of habitable Earth-like planets in our galaxy, and in the billions of galaxies in our universe.
- Earth-like iron-core rocky planets with water, plate tectonics, and carbon and nitrogen cycles, in combination with self-forming nucleic acids, lipid membranes, amino acids, and proteins as perhaps the only easy path to complex replicating autocatalytic molecular species. Earth as a catalyst for complex molecular evo devo.
Organic (carbon-based) chemistry, via a special set of molecules (autocatalytic sets of inorganic and organic enzymes, lipid membranes, and proton gradients across those membranes, driving oxidative phosphorylation redox chemistry) in a special environment, undersea alkaline hydrothermal vents, as perhaps the only easy path to autonomous RISVC molecular systems (living cells). See Nick Lane’s lovely book on the biochemistry of the origin of life, The Vital Question (2015) for more on this.
- Symbiosis between bacteria and archaea to produce eukaryotes, which Lane estimates allow eukaryotes to produce up to 200,000 times more energy per gene than prokaryotes, once they enter an endosymbiotic relationship with archaea, which become mitochondria in all complex cells. This is a fantastic example of STEM compression, the natural developmental process we find behind all accelerating change, which we discussed in Chapter 2.
- Gene regulatory networks, which control morphological development, may require a generic minimum set of gene interactions to create bilaterally symmetric body plans, and there may be generic ways these plans and networks must interact based on diffusion biochemistry to produce differentiated tissues The “hourglass model” of biological development (picture right, which conveniently looks like a phase-space funnel) describes a “phylotypic stage” of development where various animal embryos, which began with different egg morphologies, converge to look and function very similarly, and then later diverge again into their adult forms. The phylotypic morphology portal, the center of the hourglass in this picture, may be optimal, seen in all multicellular embryos based on DNA anywhere in the universe. A set of bottlenecks like this may have to emerge in all metazoan embryonic complexification, to continually prune the diversifying molecular chaos. If such portals must emerge, they always limit what local evolution can do.
- Multicellular organisms, with bilateral symmetry, eyes, skeletons, jointed limbs, land colonization, wings, opposable thumbs, social brains, language, and imitative behavior, starting out in the tree niche, as the easiest path for life to get to continuously self-improving tool use and social acceleration.
- Dominant body-plan morphologies in species, leading many of the same species forms to independently re-emerge, as in placental and marsupial mammals.
Fifty years ago, most chemists would not have had a strong opinion on whether organic (carbon-based) chemistry in liquid water was a universal constraining portal on the path to higher molecular complexity. Boron-based, silicon-based, and other non-carbon based complex self-replicating systems, in fluids other than water, were still serious alternative proposals. There were also lovely ideas for exotic organic replicators in our solar system. In 1976, Astronomers Carl Sagan and Edwin Salpeter published a classic paper on the possibility that gasbag organisms (sinkers, floaters, and hunters) could exist in the troposphere of Jupiter. These were visually depicted in Sagan’s epic science documentary series, Cosmos (1980) See artist Drell-7’s lovely adaptation (picture right).
Today’s xenobiology speculations are much more constrained by what we’ve learned in recent decades. Non-carbon based replicators outside of liquid water don’t seem able to easily replicate, vary, stably inherit, allow for selection or convergence the way organic chemistry does. Many astrobiologists and biochemists also think the first-arriving biological replicators must be like our prokaryotes and archae found in Earth-like environments with long term liquid water, plate tectonics, and hydrothermal vents. Lane’s work should help convince others that endosymbiosis is a necessary portal to all complex life, given its incredible energetics advantage over simple life.
Thirty years ago, few chemists would have been willing to argue that nucleic acids, fats, amino acids, and Earth-like planets are likely to be portals for the production of cell-based life throughout the universe. Today, we have several physicists, chemists, biologists, and complexity theorists making just this argument. Consider physicist Eric Smith and biologist Harold Morowitz, who believe biogenesis was the inevitable result of the laws of physics and chemistry, and that Earth-like geochemical environments “force life into existence.” (See Philip Ball, Was life on Earth inevitable?, Nature News 2006).
Recently, we have even found a clue that at least one of our universe’s “genes,” the finely-tuned initial developmental parameters, may be tuned to bias the emergence of prebiotic chemistry. In astrobiology, life’s use of “left-handed” amino acids is today a mystery. All our solar system’s meteorites are L-amino acids, when in the lab we form L- and R- in equal forms. Mindy Levine, a chemist who studied the emergence of chirality (left- or right-handedness in molecular shape) and its relation to biogenesis for her doctoral dissertation, argues that lie could have emerged via either left- or right-handed prebiotic chemicals, but not in any environment where there was a mix of both. For life to emerge, some process needed to preferentially enrich one or the other forms in early chemical evolution.
Some physicists have long suspected that circularly polarized radiation, which we have found radiating from supernovas, may be the mechanism that created life’s homochirality. Low energy spin-polarized radiation, such as beta particles, is most efficient way physicists currently know to create homochirality. Beta decay results from the weak force, one of the four known fundamental forces of nature, and the only one in which is handed, reacting only on particles with left-handed spin. In 2014, a clever 13-year long experiment with low-energy beta decay, radiating through an organic compound called bromocamphor, showed that these spin-polarized radiating electrons can transmit their asymmetry to organic molecules.
We still don’t know what processes formed the exclusivity of L-amino acids of our solar system, or whether other Earth-like solar systems will also be L-amino acid exclusive. I would bet they are, as such a finding will provide further evidence that we live in a developmentally life-rigged universe. We may live in a universe with a handed weak force simply because we need that handedness to get us to prebiotic chemistry with high reliability. We’re still a long way from being able to prove such claims, but they are looking good to me, from my position as an interested amateur.
Further research will need to verify Mindy Levine’s claim that either L- or R- amino acids could have taken us to life. To believe this, I would need to know that extensive molecular simulations have been done showing that R- amino acids can still create that special combination RNA and proteins that, together with lipids, allowed the formation of the first protocells. From what I remember of chirality, this would be unlikely, as different stereoisomers truly have different shape-charge interactions, and it is shape charge interactions, not general chemical properties, that get us to such highly specific assemblages as transfer RNA and all the associated transcription and translation protein machinery of life. Thus it remains possible that only L-amino acids will work, creating an important portal through which all complex biochemistry must pass. We shall see, as they say.
Recall also the Rare Earth astrobiologists, who predicted that Earth-like planets must be rare in the universe. These folks were dominant, or at least prominent, until the 1990s, when exoplanet data began arriving. Now we’re arguing over whether there should be millions or hundreds of thousands of Earth-like planets in our galaxy alone. We’ve come a long way, but we still have miles to go before science fully accepts the idea of an evo devo universe.
In recent decades, we’ve found molecular precursors for nucleic acids, fats, and proteins in intermolecular clouds throughout the galaxy, and in comets and meteors throughout out solar system. Our universe increasingly looks primed for the production of complex life, but only in very special locations. It’s pregnant with portals for life’s development that are greatly isotropic (the same or very similar everywhere) in the universe.
On Earth, molecular genetics is also helping us understand convergent evolutionary development, portals for biological form and function, at a new level of sophistication. For example, the antifreeze proteins in the blood of northern and southern polar fish appear to have been created by two entirely different genetic paths in these two geographically isolated biomes—another natural experiment. Yet the essential structure of the molecule in both sets of fish, and its adaptive benefit in their bloodstreams, is convergently the same. We can predict that fish in such cold conditions on any planet would, via evolutionary experiment, necessarily develop such molecules in their blood, because the laws of chemistry and genetics make them accessible. Once accessed, they would persist, as such features are a developmental optimization for these very cold environments.
Many molecular species replicate (RNA, viruses, prions, clays) but only one, cells, is presently continuously and recursively self-improving (evolving and developing) its replicative complexity in a way that doesn’t require other complex replicators. Many animals (crows, monkeys, dolphins) engage in tool use. But only one species, humanity, is presently recursively self-improving its tool use, originally over living generations, and now over generations of tool design and use.
There are also unique developmental advantages to simulation advances like language, math, and science, and to technological advances like sharp rocks, clubs, levers, wheels, electricity, and computers. Each of these technemes are quite defensible as portals. We’ll further explore just two of these, the wheel and the computer, a bit later in this chapter.
As a result of this kind of controversial work, the “random” evolution view of the universe, while still by far the dominant view in science, is losing ground. We are slowly returning to one of the older views that the universe is, in Fred Hoyle’s terms, a “put-up job”, a system rigged not only for diversification and random walks (evo), but for the acceleration of complexity (devo). See his book The Intelligent Universe, 1988, for more on that view. Our universe seems self-organized to be exceptionally fit for the emergence and persistence of both life and intelligence, a topic known as the anthropic cosmological principle. For a more technical survey of the evidence for life-fitness, see John Barrow et al. (eds). Fitness of the Cosmos for Life: Biochemistry and Fine-Tuning (2006).