Back in 1859, Charles Darwin released his famous theory of evolution by natural selection whereby inherent variations in the individual members of some population of organisms under consideration would eventually lead to speciation events due to those variations producing a differential in survival and reproductive success and thus leading to the natural selection of some subset of organisms within that population. As Darwin explained in his On The Origin of Species:
If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being’s own welfare, in the same way as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.
While Darwin’s big idea completely transformed biology in terms of it providing (for the first time in history) an incredibly robust explanation for the origin of the diversity of life on this planet, his idea has since inspired other theories pertaining to perhaps the three largest mysteries that humans have ever explored: the origin of life itself (not just the diversity of life after it had begun, which was the intended scope of Darwin’s theory), the origin of the universe (most notably, why the universe is the way it is and not some other way), and also the origin of consciousness.
Origin of Life
In order to solve the first mystery (the origin of life itself), geologists, biologists, and biochemists are searching for plausible models of abiogenesis, whereby the general scheme of these models would involve chemical reactions (pertaining to geology) that would have begun to incorporate certain kinds of energetically favorable organic chemistries such that organic, self-replicating molecules eventually resulted. Now, where Darwin’s idea of natural selection comes into play with life’s origin is in regard to the origin and evolution of these self-replicating molecules. First of all, in order for any molecule at all to build up in concentration requires a set of conditions such that the reaction leading to the production of the molecule in question is more favorable than the reverse reaction where the product transforms back into the initial starting materials. If merely one chemical reaction (out of a countless number of reactions occurring on the early earth) led to a self-replicating product, this would increasingly favor the production of that product, and thus self-replicating molecules themselves would be naturally selected for. Once one of them was produced, there would have been a cascade effect of exponential growth, at least up to the limit set by the availability of the starting materials and energy sources present.
Now if we assume that at least some subset of these self-replicating molecules (if not all of them) had an imperfect fidelity in the copying process (which is highly likely) and/or underwent even a slight change after replication by reacting with other neighboring molecules (also likely), this would provide them with a means of mutation. Mutations would inevitably lead to some molecules becoming more effective self-replicators than others, and then evolution through natural selection would take off, eventually leading to modern RNA/DNA. So not only does Darwin’s big idea account for the evolution of diversity of life on this planet, but the basic underlying principle of natural selection would also account for the origin of self-replicating molecules in the first place, and subsequently the origin of RNA and DNA.
Origin of the Universe
Another grand idea that is gaining heavy traction in cosmology is that of inflationary cosmology, where this theory posits that the early universe underwent a period of rapid expansion, and due to quantum mechanical fluctuations in the microscopically sized inflationary region, seed universes would have resulted with each one having slightly different properties, one of which that would have expanded to be the universe that we live in. Inflationary cosmology is currently heavily supported because it has led to a number of predictions, many of which that have already been confirmed by observation (it explains many large-scale features of our universe such as its homogeneity, isotropy, flatness, and other features). What I find most interesting with inflationary theory is that it predicts the existence of a multiverse, whereby we are but one of an extremely large number of other universes (predicted to be on the order of 10^500, if not an infinite number), with each one having slightly different constants and so forth.
Once again, Darwin’s big idea, when applied to inflationary cosmology, would lead to the conclusion that our universe is the way it is because it was naturally selected to be that way. The fact that its constants are within a very narrow range such that matter can even form, would make perfect sense, because even if an infinite number of universes exist with different constants, we would only expect to find ourselves in one that has the constants within the necessary range in order for matter, let alone life to exist. So any universe that harbors matter, let alone life, would be naturally selected for against all the other universes that didn’t have the right properties to do so, including for example, universes that had too high or too low of a cosmological constant (such as those that would have instantly collapsed into a Big Crunch or expanded into a heat death far too quickly for any matter or life to have formed), or even universes that didn’t have the proper strong nuclear force to hold atomic nuclei together, or any other number of combinations that wouldn’t work. So any universe that contains intelligent life capable of even asking the question of their origins, must necessarily have its properties within the required range (often referred to as the anthropic principle).
After our universe formed, the same principle would also apply to each galaxy and each solar system within those galaxies, whereby because variations exist in each galaxy and within each substituent solar system (differential properties analogous to different genes in a gene pool), then only those that have an acceptable range of conditions are capable of harboring life. With over 10^22 stars in the observable universe (an unfathomably large number), and billions of years to evolve different conditions within each solar system surrounding those many stars, it isn’t surprising that eventually the temperature and other conditions would be acceptable for liquid water and organic chemistries to occur in many of those solar systems. Even if there was only one life permitting planet per galaxy (on average), that would add up to over 100 billion life permitting planets in the observable universe alone (with many orders of magnitude more life permitting planets in the non-observable universe). So given enough time, and given some mechanism of variation (in this case, differences in star composition and dynamics), natural selection in a sense can also account for the evolution of some solar systems that do in fact have life permitting conditions in a universe such as our own.
Origin of Consciousness
The last significant mystery I’d like to discuss involves the origin of consciousness. While there are many current theories pertaining to different aspects of consciousness, and while there has been much research performed in the neurosciences, cognitive sciences, psychology, etc., pertaining to how the brain works and how it correlates to various aspects of the mind and consciousness, the brain sciences (though neuroscience in particular) are in their relative infancy and so there are still many questions that haven’t been answered yet. One promising theory that has already been shown to account for many aspects of consciousness is Gerald Edelman’s theory of neuronal group selection (NGS) otherwise known as neural Darwinism (ND), which is a large scale theory of brain function. As one might expect from the name, the mechanism of natural selection is integral to this theory. In ND, the basic idea consists of three parts as read on the Wiki:
- Anatomical connectivity in the brain occurs via selective mechanochemical events that take place epigenetically during development. This creates a diverse primary neurological repertoire by differential reproduction.
- Once structural diversity is established anatomically, a second selective process occurs during postnatal behavioral experience through epigenetic modifications in the strength of synaptic connections between neuronal groups. This creates a diverse secondary repertoire by differential amplification.
- Re-entrant signaling between neuronal groups allows for spatiotemporal continuity in response to real-world interactions. Edelman argues that thalamocortical and corticocortical re-entrant signaling are critical to generating and maintaining conscious states in mammals.
In a nutshell, the basic differentiated structure of the brain that forms in early development is accomplished through cellular proliferation, migration, distribution, and branching processes that involve selection processes operating on random differences in the adhesion molecules that these processes use to bind one neuronal cell to another. These crude selection processes result in a rough initial configuration that is for the most part fixed. However, because there are a diverse number of sets of different hierarchical arrangements of neurons in various neuronal groups, there are bound to be functionally equivalent groups of neurons that are not equivalent in structure, but are all capable of responding to the same types of sensory input. Because some of these groups should in theory be better than others at responding to some particular type of sensory stimuli, this creates a form of neuronal/synaptic competition in the brain, whereby those groups of neurons that happen to have the best synaptic efficiency for the stimuli in question are naturally selected over the others. This in turn leads to an increased probability that the same network will respond to similar or identical signals in the future. Each time this occurs, synaptic strengths increase in the most efficient networks for each particular type of stimuli, and this would account for a relatively quick level of neural plasticity in the brain.
The last aspect of the theory involves what Edelman called re-entrant signaling whereby a sampling of the stimuli from functionally different groups of neurons occurring at the same time leads to a form of self-organizing intelligence. This would provide a means for explaining how we experience spatiotemporal consistency in our experience of sensory stimuli. Basically, we would have functionally different parts of the brain, such as various maps in the visual centers that pertain to color versus others that pertain to orientation or shape, that would effectively amalgamate the two (previously segregated) regions such that they can function in parallel and thus correlate with one another producing an amalgamation of the two types of neural maps. Once this re-entrant signaling is accomplished between higher order or higher complexity maps in the brain, such as those pertaining to value-dependent memory storage centers, language centers, and perhaps back to various sensory cortical regions, this would create an even richer level of synchronization, possibly leading to consciousness (according to the theory). In all of the aspects of the theory, the natural selection of differentiated neuronal structures, synaptic connections and strengths and eventually that of larger re-entrant connections would be responsible for creating the parallel and correlated processes in the brain believed to be required for consciousness. There’s been an increasing amount of support for this theory, and more evidence continues to accumulate in support of it. In any case, it is a brilliant idea and one with a lot of promise in potentially explaining one of the most fundamental aspects of our existence.
Darwin’s Big Idea May Be the Biggest Yet
In my opinion, Darwin’s theory of evolution through natural selection was perhaps the most profound theory ever discovered. I’d even say that it beats Einstein’s theory of Relativity because of its massive explanatory scope and carryover to other disciplines, such as cosmology, neuroscience, and even the immune system (see Edelman’s Nobel work on the immune system, where he showed how the immune system works through natural selection as well, as opposed to some type of re-programming/learning). Based on the basic idea of natural selection, we have been able to provide a number of robust explanations pertaining to many aspects of why the universe is likely to be the way it is, how life likely began, how it evolved afterward, and it may possibly be the answer to how life eventually evolved brains capable of being conscious. It is truly one of the most fascinating principles I’ve ever learned about and I’m honestly awe struck by its beauty, simplicity, and explanatory power.