Monday weekly Series on Alternative Evolution:
If it didn’t happen by Neo-Darwinian means, how did evolution occur?
Biology’s Big Bang/s – Scaling Laws: Something Universal is going on…
Decent from a common ancestral condition?
To introduce you to the first major model of alternative evolution employed throughout this series, I will start with Eugene Koonin’s model entitled: ‘The Biological Big Bang model for the major transitions in evolution’ (now you can see where the inspiration for the title of this part of the series). It i summarised below:
Major transitions in biological evolution show the same pattern of sudden emergence of diverse forms at a new level of complexity. The relationships between major groups within an emergent new class of biological entities are hard to decipher and do not seem to fit the tree pattern that, following Darwin’s original proposal, remains the dominant description of biological evolution. The cases in point include the origin of complex RNA molecules and protein folds; major groups of viruses; archaea and bacteria, and the principal lineages within each of these prokaryotic domains; eukaryotic supergroups; and animal phyla. In each of these pivotal nexuses in life’s history, the principal “types” seem to appear rapidly and fully equipped with the signature features of the respective new level of biological organization. No intermediate “grades” or intermediate forms between different types are detectable..
I propose that most or all major evolutionary transitions that show the “explosive” pattern of emergence of new types of biological entities correspond to a boundary between two qualitatively distinct evolutionary phases. The first, inflationary phase is characterized by extremely rapid evolution driven by various processes of genetic information exchange, such as horizontal gene transfer, recombination, fusion, fission, and spread of mobile elements. These processes give rise to a vast diversity of forms from which the main classes of entities at the new level of complexity emerge independently, through a sampling process. In the second phase, evolution dramatically slows down, the respective process of genetic information exchange tapers off, and multiple lineages of the new type of entities emerge, each of them evolving in a tree-like fashion from that point on.
(Koonin 2007) article link
As you will see throughout this series, the fossil record makes a great deal more sense in the light of this type of model. Koonin’s use of the term, Big Bang, is of course with reference to the cosmological big bang – and as most of us know, biology has an equivalent sudden eruption in the form of what is often termed the Cambrian Explosion, a period just over half a billion years ago when almost all of the main body-plans (Koonin’s principal types without apparent transitional forms) came suddenly into existence, and seemingly from no certain precursors, as is the case with other rather abrupt eruption of complex life also noted by Koonin. However, as indicated above, Koonin’s model suggests a rather more silent eruption, behind the evolutionary scenes, during the major leaps of life, offering clues such as: novel genetic exchange via whole organism mergers and rampant horizontal genetic transfer across whole domains and species. I will deal with these major exchanges more in next week’s article, but for now I would like to focus more on another aspect of Koonin’s model: what I believe is a fundamental aspect of the over-arching synthesis I aim to present throughout this series.
As also alluded to above in Koonin’s Big Bang analogy, evolution follows the pattern of rapid early (inflationary) phase (think in terms of blowing up a big balloon), followed by a rapid slowing down, or stable phase. This pattern of evolution/growth just happens to correspond to a universal (or almost universal as most things we have measured turn out to have the same sigmoidal growth/evolutionary pattern). This logistics ‘S’ curve should therefore be applicable to the growth pattern of evolution itself and the growth patterns of these evolutionary seemingly seamless boundaries of leaps of complexity. This is known as a sigmoid curve (see below) where initial and slow starting conditions (we know this to be the case prior to big rapid eruption of life as the fossil record shows) – a lag phase, followed by exponential growth/eruption of complexity and then rapid stability.
Sigmoid curve or stretched ‘S’ shaped curve
Generic ‘S’ Curve type chart that applies universally growth/evolution of any system or species population
Source: FIGURE 11.5 Exponentlal growth of a colonizing population of Scots pine. Pinus sylvestris (data from Bennen 1983). http://sky.scnu.edu.cn/life/class/ecology/chapter/Chapter11.htm
Source: FIGURE 11.8 Sigmoidal growth by a population of the yeast Saccharomyoces cercvisiac (data from Gause 1934).http://sky.scnu.edu.cn/life/class/ecology/chapter/Chapter11.htm
Life fortunately is an open, not a closed system as in the bacteria in a Petrie Dish. A whole system is established, but based on principles of the former, can take another quantum leap if the new novel conditions are introduced and wider horizons can be exploited before stability kicks in. Nature has been making use of all opportunities that opened up as the environment changed working in a feedback loop and driving complexity and stability within each level of life. The elongated part of the logistic curve (the exponential part) as in the rapid colonisation of plants or trees in the diagrams above, or the explosive nature of the internet after all the independent parts of technology required were in place to make the leap as you will see further on, all follow the pattern of the Sigmoid growth curve. Evolution itself appears to have taken a course that can be mapped by a continuous sequence of increasing complexity (on scales) of discrete, but linked ‘S’ curves according to the pattern of a feedback mechanism with the environment as new and novel materials, products, environments and novel genetics come into the equation. A good illustration of this continued growth after stabilisation of one fundamental form of life can be seen in a business model below in an article entitled: Jumping the S curve requires frequent injections of new blood and a continual shake-up of the top team.
One well-known business example most of us would be aware of is Facebook: I have linked to the article here https://hbr.org/2012/09/throw-your-life-a-curve/
Their ‘S’ Curve representation says it all:
Source: Méndez and Johnson 2012
As this pattern corresponds to a universal and so far seems to apply to all complex systems and their evolution as well as the growth forests, the development of plants, growth of bacterial colonies and even cities and the internet and just about anything that has been studied from the point of view of growth and development/evolution, it would seem a good place to begin in attempting to formulating an over-arching synthesis and model for an alternative evolutionary perspective. For instance, the ‘almost’ universality of Sigmoidal growth curves as they apply to biological complexity is highlighted below:
Growth models based on first principles or phenomenology?
…Still largely missing, however, is a theoretical framework for understanding the mechanisms that affect whole-organism growth trajectories. So questions such as why growth curves are almost universally sigmoidal, what controls the final or mature body size, and what affects the allocation of energy and materials to growth and development remain largely unanswered.
Thanks to the work of physicists like Geoffrey West and others and the application of scaling laws to biological systems, answers many mysteries about otherwise, seemingly mind-boggling complexity of biological life and evolutionary growth and at the same time demonstrate the surprisingly simple principles of life that underpin such complexity. I will return to some aspects of their work further on, but in the meantime here are a few quotes from West that I believe highlight the significance of these universals as applied to biology:
In an article entitled: Of Mice and Elephants: a Matter of Scale by GEORGE JOHNSON
Published: January 12, 1999 West in quoted as follows:
”Everything around us is scale dependent,” Dr. West said. ”It’s woven into the fabric of the universe.”…
”It is truly amazing because life is easily the most complex of complex systems,” Dr. West said. ”But in spite of this, it has this absurdly simple scaling law. Something universal is going on.” …
Other articles worth reviewing http://jeb.biologists.org/content/208/9/1575.full
Video on you tube where West explains a great deal
So to apply and interpret Koonin’s big bang model of early evolutionary development in light of the fossil record and the principle of scaling laws, it would go something like this: There is a slow build until all the resources are in place (lag phase), which we know from the fossil record (the base of the elongated ‘s’), then the system takes a quantum growth spurt (the sinuous length of the ‘s’) as it scales up to an entirely new level of complexity and then stabilisation of the overall system as it has reached its full potential of complexity or growth capacity. The other eruptions of complexity can be seen to follow the same pattern on different scales that can be illustrated as interlinking ‘S’ curves. Recall the lag phase for the start of the ‘S’ curve before it goes exponential. There is a lot of work behind the scenes that is not obvious, not seen or observed, prior to exponential growth. It is only when everything is in place that this growth can go the way it does. We know for example that there was a great deal going on behind the scenes prior to the Cambrian explosion of life (or the Big Bang in Biology).
Source: FIGURE 1. Atmospheric oxygen levels during the history of the planet
The estimated oxygen concentrations in the Earth’s atmosphere since the planet formed ∼4,550 million years ago and major events in evolutionary history including the evidence for the first simple cells, the beginning of photosynthesis, the appearance of green plants, and the Cambrian explosion during which metazoan radiation took place.
The seemingly universal Sigmoidal logistic curve may ultimately help to explain why all this genetic exchange across entire domains of life didn’t keep morphing and come to be so stable and FIXED with only micro-changes occurring today. In other words, why bacteria still remain bacteria, even though some of them have hitched a ride in our guts and are essential in a co-evolutionary way (symbiotic relationship) to not just our well-being, but to the planet as a whole. Why fish are still fish and why some higher primates went on to become human while others specialised as other forms. Imagine the mess of the planet if everything was still morphing into complexity instead of each fundamental “type” once it had reached its natural level of complexity stabilising in that form? It appears to all come down to efficiency (metabolism in the case of organisms), judging by the research of West and others, and an organism’s drive to use energy efficiently, an exchange at a cellular and fractal-like biological networks, a striving towards efficiency of the whole system and all its parts (its organisms) in a positive feedback mechanism that has itself followed the ‘S’ curve standard model for growth in the universal system we find ourselves in. These principles as applied to biological complexity and evolutionary development are not new ideas.
Another article by West and others is linked here and explains universal scaling laws:
For example, in the above article they note the important research which offered explanations of patterning and chemical self-organisation. This research dates back to the turn of the 20th century and is relevent today in going beyond genetic coding for all variation on the planet goes back to the mathematical formula and universal laws seen within our natural world and indeed, everywhere outside the planet where we have looked thus far. In his theory of mathematical explanations and predictable growth patterns of transformations in biology, Wentworth, D’Arcy Thompson, born the year after Darwin published his famous book on ‘On the Origin of Species’. D’Arcy Thompson published on the Growth and Form 1917. Thompson explained that all form and shape in nature was underlain by principles of repeating patterns and could be understood in a similar way to how physics and maths applies universal laws to other complex systems. This research is being taken seriously as the NASA scientists are using Thompson’s research and book of life to find extraterrestrial life as seen below. I find it interesting that they didn’t take ‘On the Origin of Species’ with them. On the Nasa website the article is entitled:’Who Wrote The Book of Life? Picking Up Where D’Arcy Thompson Left Off’
NASA scientists are using Thompson’s biomathematical studies of life forms on Earth to postulate about life forms throughout the universe. There are certain universal conditions that will always affect the shape of a life form, wherever that life may be.
“Everywhere Nature works true to scale, and everything has a proper size accordingly,” wrote Thompson. “Cell and tissue, shell and bone, leaf and flower are so many portions of matter, and it is in obedience to the laws of physics that their particles have been moved, moulded and conformed.” … Gravity, for instance, acts on all particles and affects matter cohesion, chemical affinity and body volume. Other influences that are consistent throughout the universe are temperature, pressure, electrical charge and chemistry.
Similar ideas were further developed and formalized in the mathematical form by A. M. Turing (1952) (perhaps better known for his pioneering code cracking abilities during World War II), in his publication entitled: The Chemical Basis of Morphogenesis, http://www.dna.caltech.edu/courses/cs191/paperscs191/turing.pdf
It explores mathematically the chemicals during development and how these can account for many patterns seen in the natural world. More recently Turing and his ideas are being supported by our deeper insights into biology and development and the world of physics, maths and biology are converging as they once did back in the old pre-Modern synthesis days as seen in the work of scientists such as biophysicist Stuart Kauffman who proposes:
…a new “fourth law of thermodynamics” – an inherent organizing tendency in the cosmos that counteracts the entropic influence of the Second Law. “A few deep and beautiful laws may govern the emergence of life and the population of the biosphere”
(THE SYNERGISM HYPOTHESIS p.7).http://journals.isss.org/index.php/proceedings56th/article/viewFile/1932/658
All of these concepts and models mentioned thus far, offer mechanisms for biological evolution as they are underpinned by well-understood behaviours of natural physical forces that organise, shape and form any evolutionary system. A good way of maybe thinking about this over-arching principle and how it seems to apply to biological evolution, is to use a well-known system that evolved in the manner akin to development of the species. That is the evolution of computers and the emergence of the internet.
Evolution of Internet compilation by Digging up the future. Credit for large cartoon image on right (the internet road and PC) http://www.buzzfeed.com/expresident/whats-your-earliest-internet-footprint#.qszBRmAwK
All the parts had an independent development/evolution, operating (functioning as self-contained units) until efficiency (electricity and eventually the micro-chip) within these systems coalesced as these technologies converged and amalgamated to form the main modules of the personal computer and the internet exploded into life. It wasn’t that the monitor out-competed the TV, or the abacus became extinct and ultimately was replaced by the first computing machine, falling by the wayside until something better came along in the form of giant computing beasties, munching and spewing out punch-cards once gainfully employed by the great textile looms. Or the silicon chip was the only means of doing big code breaking. Nor was the mechanical type-writer a dying breed as it evolved to be an all singing, all dancing electric slim-line model, to ultimately be replaced by the keyboard. No, all these technologies were really useful and great innovations of their time, always paving the way for what was ultimately to come, but still operating independently and happily functioning just as they were with some modification (modernisation) according to available resources and innovations of the time. It is the principle of their design and function that persisted until all of these technologies suddenly converged into a super technology,
Technologies Big Bang, each acquiring the principal functions of the other or took cues from the preceding system. Mother Nature wastes nothing and as we are talking about living systems and not man-made types, she has kept all her models and previous versions that are still essential to all of life from the very small to the very tall. But in a way, we keep our own older technology as curiosities of piecing together the past by displaying them in museums. The point being, that the computer (personal) and the internet evolved from the principal design and function concepts of the previous inventions. Nature seems to build upon systems of efficiency and it is these systems and innovations that inform the basis and build the foundation of what comes later. It does not have to be linear common descent through a single pieces of technology, say, the telephone to the mobile or cell phone, but the fundamental concept of telecommunications – the means of sharing information across vast distances, that merged with visual displays (output systems) and keyboard (input systems) and computation power from an abacus to punch-card/binary code systems of information connected electronically to fuel and run the whole internet/phone or computer device (the interface) that converged and went exponential when everything was in place, to become greater than the sum of its individual parts. Biological evolution would appear to be the same in principle where bigger is better is the name of the game in Mother Nature’s domain. and small is best in the technology game – the principle of efficiency is fundamentally the same.
Similarly, cellular life, not cellular phone life, and metabolism evolved first and networks of bacterial colonies into fungal networks that helped spawn the later plants and broke down minerals in rocks etc and then the microbial world to process the soils etc. This would take a few books to describe, but there is a great deal of preparation and a hidden and silent evolutionary complexity going on before the seemingly sudden eruption of life. One part of the system does not work in isolation to the other. For example, the oxygen and carbon cycle and the atmosphere and photosynthesis within air-breathing organisms – it’s all symbiotic and dependent. Yet, these are whole systems that seem to co-evolve. We cannot study species complexity without seeing it in the context of its environment. The eco-system has to evolve in order for the organisms to evolve within it. I’ll return to this concept of ‘no species is an island’ shortly, but let’s now return to these amazing universal patterns and how they apply to biological life. For instance, in West and Brown’s biologically applied scaling laws, entitled:
The origin of allometric scaling laws in biology from genomes to ecosystems: towards a quantitative unifying theory of biological structure and organization they state the following:
.., all organisms share a common structural and functional basis of metabolism at the molecular level. The basic enzymes and reactions are universal, at least across the aerobic eukaryotes. Additional general rules based on first principles determine how this molecular-level metabolism is supplied and regulated at higher levels of organization: from organelles, to cells, to organisms, to ecosystems. The most important of these rules are those relating to the size of the systems, including the body size of the individual organisms, and the temperature at which they operate. Our theory of quarter-power scaling offers a unified conceptual explanation, based on first principles of geometry, biology, physics and chemistry for the size-dependence of the metabolic process. The theory is based on generic properties of the metabolic distribution networks in simplified, idealized organisms.
There are scales of complexity within scales of complexity and we are not just talking reptile or fish scales either. The pattern emerges via metabolic complexity of the emergence of complexity itself seen in the fossil record and the living system. There is another scaling law that would appear to universal – literally, and that is the scaling law for all organised matter. See below, for one example of this and as biological systems are also organised matter, it does not take a leap of imagination to propose: “That something universal is going on…” as noted earlier by Geoffrey West and others, as physicists are well used to the applying such universals to understanding our universe, why shouldn’t they apply to biology?
In an article interview with West entitled: Yeah, but what about the crayfish? dating by Edwin Cartlidge the following is of interest.
A different mind set
The work has drawn praise from many biologists, including the popular science writer and Oxford professor Richard Dawkins, who describes it as “a theory of enormous power, explaining a huge range of facts with great economy”. … “In general,” he says, “although this was not true of my collaborators, biology tends to be dominated by a certain type of person in the opposite way to physics. They are always looking at the particular, and everything is an exception.” He says he does not understand how such people can work in science if they do not believe there are such things as universal laws. “If you had biologists working, for example, in nuclear physics you would have someone working on deuterium and then someone else working on helium and they would not realize they were working in the same field.”
What emerged closely approximated a so-called fractal network, in which each tiny part is a replica of the whole. Magnify the network of blood vessels in a hand and the image resembles one of an entire circulatory system. And to be as efficient as possible, the network also had to be ”area-preserving.” If a branch split into three daughter branches, their cross-sectional areas had to add up to that of the parent branch. This would insure that blood or sap would continue to move at the same speed throughout the organism.
The scientists were delighted to see that the model gave rise to three-quarter-power scaling between metabolic rate and body mass. But the system worked only for plants. ”We worked through the model and made clear predictions about mammals,” Dr. Brown said, ”every single one of which was wrong.”
In making the model as simple as possible, the scientists had hoped they could ignore the fact that blood is pumped by the heart in pulses and treat mammals as though they were trees. After studying hydrodynamics, they realized they needed a way to slow the pulsing blood as the vessels got tinier and tinier. These finer parts of the network would not be area-preserving but area-increasing: the cross sections of the daughter branches would add up to a sum greater than the parent branch, spreading the blood over a larger area.
After adding these and other complications, they found that the model also predicted three-quarter-power scaling in mammals. Other quarter-power scaling laws also emerged naturally from the equations. Evolution, it seemed, has overcome the natural limitations of simple geometric scaling by developing these very efficient fractal-like webs.
Mammals have richly branched air tubes, but they are confined to special organs, the lungs. Fish do a similar thing with gills. Trees use their richly dividing branches to supply their leaves with water and pump sugars back from the leaves to the trunk. The 3/4-power law is derived in part from the assumption that mammalian distribution networks are “fractal like”…
… This relationship seems to hold across the animal kingdom, from shrew to blue whale, and it has since been extended all the way down to single-celled organisms, and possibly within the cells themselves to the internal structures called mitochondria that turn nutrients into energy.
One could say that this is metabolic speciation as it is the fundamental forms of metabolism and their scales of complexity are what define the broad spectrum of species from broccoli to bacteria and from fish to frogs and mice to men. Mammals fall within the metabolic to scale ascending line in discrete ratios, although overall they all broadly fall along the line according to scale. The unicellular organisms are as would be expected, occupying the lower end of the evolutionary spectrum. There would appear to be a correlation between the origin and main species type and time. The simplest and smallest organisms arise first as seen in the fossil record. But here is what I find most interesting, note the fundamental leap along the axis (discontinuous line for each fundamental species type). Could this represent a corresponding leap in evolutionary metabolic complexity according to their fractal networks? Although, the organisms as a whole sequence follow the underlying three-quarter scaling law, the discrete units falling along this line of descent, from the tiniest to the largest would suggest fundamental scales of complexity according not just to size, but according to the metabolic complexity of the organism itself. In other words, a mouse-sized lizard cannot be plotted within the higher scale of metabolism, but remains fundamentally a lizard. The mouse was not once a lizard and became a complex mammal over time via its ancestral inheritance, but evolved a more complex fractal-like network that allowed it to become, in the end, a mammal.
https://universe-review.ca/R10-35-metabolic.htm for diagrams and explanations
The following chart taken from this paper disputing universal scaling laws applying across the board to all species, is of interest as it is used to illustrate that “scaling exponents of fish, amphibians, reptiles, birds and mammals are significantly heterogeneous” (White et al – Abstract 2006).
Scaling relationships between SMR normalized to a body temperature of 38 °C and body mass for mammals, birds, reptiles, amphibians and fish. Q10 values used for temperature normalization are presented in table 1, as are OLS (pictured) and RMA regression parameters
(Source: Figure 1 from White et al 2006)
In other words, these metabolic rates to mass are more diverse and varied than the predicted universalism scaling principle suggests. However, as West et al point out, that they are looking for universals and trying to explain why these principles drive and underlie complex biological forms in the first place and of course, these laws and their application to complex biology, are going to vary somewhat when looking at the smaller picture. The over-arching bigger picture is a whole lot more informative and revealing. For instance, West states:
”Physicists tend to look for universals and invariants whereas biologists often get preoccupied with all the variations in nature,” Dr. Brown said… Dr. West liked to joke that if Galileo had been a biologist, he would have written volumes cataloging how objects of different shapes fall from the Leaning Tower of Pisa at slightly different velocities. He would not have seen through the distracting details to the underlying truth: if you ignore air resistance, all objects fall at the same rate regardless of their weight.
Dr. West is not too bothered by these seeming exceptions. The history of physics is replete with cases where an elegant model came up against some recalcitrant data, and the model eventually won.
As I said earlier, some inverse measurements of scale reflect the universal scaling law for all organised matter as reflected in the diagram below. Furthermore, the diagram also shows discrete fundamental scales of complexity (principal types as described by Koonin, may be a better way of viewing these groupings according to species complexity and/or evolutionary timing). However, these forms still broadly following the main power law principle.
Source: Figure 2: The natural logarithm of body mass-corrected relative brain size vs. inverse temperature in vertebrates.
Relative brain size is expressed as a percentage of body mass, body mass is expressed in grams, and temperature is in degrees Kelvin (T)
For example, across space, one might expect gradients in brain size with elevation, latitude, or climate depending on the degree of temperature change and the taxonomic group in question. And across time, one might expect changes in brain size during the transition from water to land or the evolution of endothermy as these events involved changes in species’ temperatures and aerobic capacity (Bennett & Ruben, 1979). One could also speculate on the possibility of phenotypic plasticity in brain size with respect to temperature.
Now I thought at this point it might be a good idea to show you just how universal these scaling laws seem to be. As I indicated above, physicists really don’t have an issue recognising the complexity of life and systems being organised according to laws, equations and principles: it’s what most physical scientists and mathematicians do – apply their findings to discovering how the world and universe works. For instance, in a science paper entitled: SCALE UNIFICATION – A UNIVERSAL SCALING LAW FOR ORGANIZED MATTER by Nassim Haramein, Michael Hyson and E. A. Rauscher, I have taken a snapshot to show you the universality of this type of scaling law. Don’t worry about understanding the details of their measurements, just know that the scale at factors of predictable ratios of mass to frequency in this case is truly universal as it plots and rises on a predictable scale and holds true for the atomic to the galactic level of life.
Do notice, however, that they mention eukaryotic cellular life and its relevant scale nano-scale. So returning to biological systems (or organised matter on another scale) as seen above, the metabolic charts – metabolic rate to size ratio (the ¾ scaling power laws) is exactly the same in principle of its scaling laws and is generally applied as described by West et al, to metabolic rate to mass of an organism which broadly scale in complexity according to mass and rate. These predictably scale on a slope of scaled complexity accordingly. These scales (reversing the ‘x’, ‘y’ axis) are uncannily similar to the organised matter scale and reflect the inverse logarithm scales plotted above for temperature dependent brain size. Now as we are staying with the universal themes, recall that these logarithm scales are not unlike our exponential growth part of the elongated ‘S’ curve or Sigmoidal growth/evolution logistic.
Now coming back down to earth, the brain study above and its relationship to temperature, or the Cambrian explosion of life showing an exponential growth curve corresponding to the rise in oxygen levels, point to the fact that the evolution of a species, or indeed, the evolution of the planets or stars, can only be understood in the context of all their fractal parts. Environment and conditions of interaction, whether they are electro-chemical at the cellular /molecular level or the nano-scale of interactive atomic particles, the context for exponential evolution, after a lag phase of culminating factors and then to stability, has to be understood. For organisms, it is their ecological environment and their chemical/molecular environment when developing either as an existing organism or a developing species. This will make much more sense as the series continues.
Factors operating in the environment during evolutionary development are key to understanding how the species emerged. What was the temperature? How would this affect the evolutionary trajectory of a species (initial conditions are sensitive and can have a massive outcome in the end. This is a principle in chaos theory trying to explain the dynamics of complex systems coming into order from disorder – otherwise known as the butterfly effect). This, concept, (perhaps not surprisingly) also is applicable to evolutionary biology and developmental studies (EVO-DEVO) for short. Certainly nutrients and protein intake etc would be very important factors and basically, what a developing organism munched on in its primordial pond. The important point in this model is the interplay between speciation and environmental interaction particularly during developmental stages of the species types, and their underlying principles of growth and development (such as scaling and growth laws) that have the potential to allow us to rewind evolutionary history and view it from an entirely different perspective. Take for example, a brain study of vertebrates and the suggestion that we may have been barking up the wrong evolutionary tree:
‘EVOLUTION OF VERTEBRATE BRAINS’
“…The simplistic … concept of evolution ranks organisms on an ascending scale that is presumed to reflect evolutionary history … as in fish-to-frog-to-rat-to-cat-to monkey-to-human. While this concept is unfortunately widely and deeply embedded in the public consciousness, it is completely unsupported by the massive amount of data on evolution, not only for the brain but for all characters across the board”.
Butler instead suggests going from a common ancestral condition to more specialised forms of differentiated species. Interestingly, these ties in with a much older theory of evolution based upon laws of embryology.
Von Baer described his laws of embryology in both editions of his book Über Entwickelungsgeschichte der Thiere [On the Development of Animals], published in 1828 and 1837. In this work, von Baer reviewed existing information on the development of vertebrates. He used the information in this review to extrapolate his laws. These laws, translated by Thomas Henry Huxley in Scientific Memoirs are verbatim as follows:
- […] the more general characters of a large group appear earlier in the embryo than the more special characters.
- From the most general forms the less general are developed, and so on, until finally the most special arises.
- Every embryo of a given animal form, instead of passing through the other forms, rather becomes separated from them.
- Fundamentally, therefore, the embryo of a higher form never resembles any other form, but only its embryo.
In other words: going from the generalist type species to the specialist species from a shared common ancestral condition rather than a linear descent from a single ancestral line. After all, it cannot be a linear descent. One, you have to take environment into the picture, such as temperature dependency of brain size etc (which people like De Baer would have fundamentally underpinned his theory with this principle of environmental shaping during both evolutionary and embryological development) and two, all the genetic exchange across whole domains of life would make it impossible to track down your ancestor/s due to the web-like nature of the family bush. I don’t mean the Bush family. So rather than looking at a direct common ancestry model of evolution based solely on genetic inheritance as the great unifying code of life, I am attempted to assess evolution from the perspective of simple underlying principles (albeit a little idealised), of metabolism which is essentially a chemical/molecular process in exchange with its environment and is the total of all the chemical reactions an organism needs to evolve and sustain itself. The genetics as you will see further on, are important in supplying all manner of raw genetic material from which the environment acts upon to guide the organisms towards being fully efficient organisms within the confines of their metabolic condition, leading to the great unifying principle of biological life that shows clear scaling laws and is all about energy conversion whether you are bacteria, a broccoli flower or a billionaire. If we view the fossil record in the light of Von Baer’s principles of scaling of the species and going from the shared common features before divergence into more complex and diversified forms, or Butler’s common ancestral condition rather than simplistic and literal common descent, then a model of a very different form of evolution begins to emerge.
For instance, metabolically speaking, we are not top of this evolutionary tree – elephants and whales are because they are bigger mammals than ourselves. But as mammals, we out-rank in complexity of our warm-blooded metabolic system, the cold-blooded (simpler) vertebrates such as lizards and amphibians. In turn, these vertebrates are still more complex than their fishy counterparts that never fully developed a system for being more than cold-blooded non-oxygen breathing, gill filtering and the magical metamorphosis of the chordate (of fish, amphibians and other primitive land-walking tetrapods – meaning paired limbs) that can go from a primitive floating, pooping, filter feeding, replicating invertebrate with a notch-chord and beginning of a brain to a full-blown vertebrate with limbs and a whole new breathing system would seem like a miracle indeed, unless we didn’t know any better. I hope that you are beginning to see what I am hinting at here as an alternative to walking fish story of evolution.
But there is more evidence to present, before this will begin to make full sense as a rather radical explanation of evolution, not by direct common descent but, by epigenetic modification – I’ll get to this topic next week.
The gradient slopes presented above for metabolism according to mass and the environmentally linked brain size to temperature inverse diagram, clearly show that warm-blooded animals such as birds and mammals are fundamentally distinct organisms to their cold-blooded tetrapod types. Even within this group of vertebrates with cold-blooded metabolism, when they are plotted according to species type and say, brain size to temperature, there are discrete groupings of complexity emerging within these classes of species. If we apply the concept of Von Baer’s laws and principles of embryology and the generalist to the specialist principle, the evolutionary picture begins to look rather different to our current standard model. I will give clear examples throughout this series of the actual fossil record and how easy it is to interpret in the light of Von Baerian principles. If we apply this to evolutionary development of the fundamental species forms (vertebrate/invertebrate/warm-blooded/cold-blooded) we can see not common ancestral descent, from fish to amphibian and from reptile to mammal, but discrete metabolic systems that run independently within the main species forms.
Could the systems to space-fill in the most efficient way depending upon the ancestral primordial pond have changed the trajectory of these organisms, going from an ancestral COMMON CONDITION rather than via direct common descent? Surely as the diagrams suggests, fish are not going to suddenly shift their metabolism whole system supply of nutrients and energy just to become an amphibian. Never mind the difficulty of putting on fractal fishy fingers and a new skin and breathing apparatus. I’ll return to the supporting evidence for this proposition, offering an alternative explanation later on in this series. But just to round this section up, regarding the bigger scaling picture for now, the overall model should be beginning to conjure up fractal-like scales of whole systems/organisms, like a telescope of unfurling discrete, but connected and nested extensions of increasingly complex life-forms and like the telescope, all its parts are required to work together as one system.
These leaps in complexity according to the unifying system of size (scale) and metabolic rate in discrete fundamental scales of complexity is a clue to how evolution itself may have erupted at each fundamental scales and can be correlated to massive changes in environmental conditions. How species at a fundamental of primitive generalists can continue to refine their form and specialise to become fully developed and mature (stabilised) grown up species. Fully formed and without transitions as Koonin noted in his Big Bang model. There may have been many big bangs throughout evolution, just that the later ones got a little quieter than the initial ones like the Cambrian explosion. Obviously, the genetic exchange across all species domains of life helped fill these nested leaps of complexity and a highly coordinated manner, so it as each system of complexity erupted onto the scene, what mechanism may have led to the stabilisation of these morphs, bringing them to point of energy efficiency and in tune with their particular eco-system as they reached their full potential of metabolic efficiency and stabilised as fundamental types of organisms at a molecular/genetic level? The answer may lie in part in a study by Adrian P. Bird:
“Preliminary estimates suggest that gene number, and hence biological complexity, increased suddenly at two periods of macroevolutionary change (the origin of eukaryotes and the origin of vertebrates), but otherwise remained relatively constant. As the genome is in constant flux, what normally constrains the number of different genes that an organism can retain? Here, I suggest that an important limitation on gene number is the efficiency of mechanisms that reduce transcriptional background noise. The appearance of both eukaryotes and vertebrates coincided with novel mechanisms of noise reduction”.
In other words, nature seems to have a stabilising (silencing mechanism) when it becomes fully efficient and I suppose it also helps keep all those morphing novel forms of genetic exchange across whole domains of life and their resultant forms, into some sensible order as nature stabilises the energy exchange between the biological systems and the environment. The other important aspect of the scaling laws and how they might apply to evolutionary development as well established for the individual growth and development of an existing species or present-day population, is the fact that all this genetic novelty has obviously not only been genomically silenced and stabilised, whether it is the evolution of photosynthesis in relation to oxygen levels in the atmosphere, or as an organism or embryo is developing in a particular womb or primordial pond environment, it is all about environmentally driven evolutionary development. When we are talking about the genetic aspect of environment and an organism, we need to bring epigenetics into the equation. Epigenetic expression of existing genes would appear to be the means, by which these highly ordered and efficient organisms have evolved to be so perfectly adapted to their environments.
The topic of next weeks’ discussion will therefore be about the epigenetic revolution going on in evolutionary thinking and how epigenetic factors are the competent user via epigenetic expression, of the genetic toolkit and therefore is the all important factor when deciphering how organisms became shaped and formed according to their environments and needs. It is epigenetics that have acted upon the novel genetics that have been seemingly passed between so many species and whole domains of life (as described above in Koonin’s model, ranging from mergers of whole independent organisms, to direct transference of genetics between species – HGT – horizontal gene transfer). HGT is quite different from the lateral way that most of us understand genes being passed on via your parents, grandparents, ancestors etc, but in principle it is the same: it passes on traits and characters. However, their is an entire imprint on the epigenome of genetic expression to take into account that is the flexible part of genome remodelling – this too is inherited or passed on between species and domains of life. In addition to mergers of previously independent species; the coordinated networks of microbial life forming whole new organisms, and HGT resulting in things like cow’s genomes having no less than 1/4 of snake genetics, hybridisation should also be added to the mix. Although this is not noted in Koonin’s model, when one views the evidence for hybridisation between more complex species that also cross species barriers we once thought impassable, we have to rethink how epigenetic processes and other factors such as: remodeling of genomes (via mobile genetic elements) – jumping genes, and all in combination as leading, ultimately and seemingly, rapid to new and novel forms of characters, traits and whole new stabilised and fundamentally fixed species (fish remaining fish, but going on to be all micro-tuned variations on the theme of fish etc). All of this, of course, has serious implications for our current model of linear branching – tree of life scenario and its presumed genetic and ancestral relationships. It means that life is more flexible and web-like than anyone could have imaged. Therefore, it would simply not be possible to find your missing ancestors, even if you tried looking for it, because it may not have been an entity, a thing, but a mechanism for adaptive evolution.
Drop by Monday week for the next part in the series asking the question: Well, if it wasn’t by Neo-Darwinian means, how did evolution occur?