The mega‐evolution of life with its three memory systems depends on sender–receiver communication and problem‐solving. A narrative review

It should be the ultimate goal of any theory of evolution to delineate the contours of an integrative system to answer the question: How does life (in all its complexity) evolve (which can be called mega‐evolution)? But how to plausibly define ‘life’? My answer (1994–2023) is: ‘life’ sounds like a noun, but denotes an activity, and thus is a verb. Life (L) denotes nothing else than the total sum (∑) of all acts of communication (transfer of information) (C) executed by any type of senders–receivers at all their levels (up to at least 15) of compartmental organization: L = ∑C. The ‘communicating compartment’ is better suited to serve as the universal unit of structure, function and evolution than the cell, the smallest such unit. By paying as much importance to communication activity as to the Central Dogma of molecular biology, a wealth of new insights unfold. The major ones are as follows. (1) Living compartments have not only a genetic memory (DNA), but also a still enigmatic cognitive and an electrical memory system (and thus a triple memory system). (2) Complex compartments can have up to three types of progeny: genetic descendants/children, pupils/learners and electricians. (3) Of particular importance to adaptation, any act of communication is a problem‐solving act because all messages need to be decoded. Hence through problem‐solving that precedes selection, life itself is the driving force of its own evolution (a very clever but counterintuitive and unexpected logical deduction). Perhaps, this is the ‘vital force’ philosopher and Nobel laureate (in 1927) Henri Bergson searched for but did not find.


Introduction
This review is my 'Yes, of course' physiology-based answer to Laland et al.'s question (2014): 'Does evolutionary theory need a rethink?' Since Darwin's On the Origin of Species by means of Natural Selection… (1859), the scientific world, in parallel to the economic world, has drastically changed.In biology, many novel disciplines that did not exist in Darwin's and Wallace's (1871) time, e.g.genetics, cell biology and in particular physiology, did not exist at all or only existed in a nascent form.To date, these disciplines are grown-ups, each with its extensive new vocabulary and experimental methods.They continue to expand and to advance ever newer insights.Some have already been incorporated in neo-Darwinism.But more needs to be done (e.g.Wikipedia, 'Central dogma of molecular biology'; Danchin et al., 2011;Laland et al., 2014;Pigliucci & Müller 2010;Pookottil, 2013;Stoltfus & Cable, 2014;Shapiro, 2016Shapiro, , 2021;;Barton, 2022;Gontier, 2015Gontier, , 2017;;Jablonka & Lamb, 2014, 2020;Noble, 2013Noble, , 2017;;Smith et al., 2018;Villarreal & Witzany, 2019;Dawkins & Noble, 2023).According to Shapiro (2021), 'a third way' of thinking on evolution is necessary.He argued that the 'Modern Synthesis' , which was based on Darwin's preference for phyletic gradualism, necessary to elevate natural selection to the sole force determining the direction of evolutionary change, no longer holds.Initially after its launch in 2014 (see Shapiro, 2021), the Third Way idea met with quite some (vigorous) opposition.To date, its rate of approval has dramatically improved.As one of its supporters, I think that an all-round theory of evolution should not just explain the coming into existence of new species by the principles of micro-and macro-evolution, and not only emphasize the genetic mechanisms involved, but address the evolution of life in all its complexity (i.e.mega-evolution).This is a higher level than macroevolution.It necessitates that the term 'life' should be defined first.This is thought to be impossible by many, given the limited intellectual capacity of the human brain.Yet, it can be done (De Loof and Vanden Broeck, 1995;De Loof, 2015a), even without invoking any not yet fully documented biological principles.The key? First, ask the right questions; second, involve the principles of communication, and see how these enable problem-solving; third, deduce how the latter, in concert with the possibilities offered by (molecular) genetics, contributes to adaptation (De Loof, 2004, 2015a, c, 2017, 2022).This invites one to bend the well-known one-liners 'struggle for life' and 'survival of the fittest' into 'the best problem-solvers for overcoming obstacles of all sorts have better chances for being successful in survival and reproduction' (De Loof, 2015c).By doing so, a new paradigm emerged, not through a single serendipitous flash of new insight, but through a multitude of small steps that gradually -over about 50 years -advanced the principles of communication/problem-solving as at least equally important as molecular genetics in improving the wording of evolutionary theory.The very essence of this fundamental change in paradigm, which is easy to teach, is summarized in Fig. 1.
In the present review only selected topics are covered.I highlight in particular some advances that emerged from my fields of experimental expertise, namely general physiology, comparative endocrinology of animals and developmental biology.
'Physiology is rocking the foundations of evolutionary biology' Charles Darwin is best known for his ideas on the links between genetic inheritance and evolution.Denis Noble (2013Noble ( , 2022) ) reminds (evolutionary biologists) of 'a largely ignored fact, namely that Charles Darwin, in the last decade of his life (1872-1882) got very interested in physiology, a discipline that he viewed as the way forward in answering fundamental questions about inheritance, acquired characteristics, and the mechanisms by which organisms could achieve their ends and survival' .Noble, who for many years pioneered linking evolution and physiology (Noble, 2008(Noble, , 2013(Noble, , 2017(Noble, , 2018(Noble, , 2022;;Dawkins & Noble, 2023) is, rightly in my opinion, very outspoken in his wording: 'It is time for physiology to come to the rescue of evolutionary biology by providing the evidence for the causal mechanisms of evolutionary change, which Darwin himself believed was lacking from his theories' Noble (2022) (and which are still lacking from the standard theories today).
A major problem arises: both genetics and physiology have become very comprehensive disciplines, with ever expanding new vocabularies.Their integration, if do-able at all, likely requires the formulation of a novel paradigm.In this paper, I recount how I became, unintentionally, interested in evolutionary theory, and how I became aware that the basic activity of sender-receiver communicating compartments -which transfer information -might be a prime candidate for representing the very heart of such a paradigm.That implied a drastic shift in thinking: cells not only have a nucleic acid-based genetic memory, but also both a cognitive memory system and an electric memory system (De Loof, 2022; see below).The last two have been overlooked in the Modern Synthesis and its extensions.Three complementary memory systems harbour many more possibilities for adaptation and evolutionary change in general than just a single one.

State-of-the-art in the 1960s
In the early 1960s, when I was a student at Ghent University's Faculty of Agronomy, evolutionary theory and Darwin's approach were not a hot topic in the teaching of general biology and not even of genetics.There were several reasons.In the western world the static worldview, as formulated in the 'Book of Genesis' , was widely literally accepted: God created all species one by one, and their form/anatomy hardly changed in the course of time.No wonder that the common descent principle, which is today very well documented, was initially regarded with great scepticism.There was more interest in the functioning or physiology of plants and animals, as well as in improving their commercial value, than in the theoretical discussions by biologists of the origin of species.Improving the quality and economic value of food were an ongoing issue and concern for farmers and breeders, who had worked for generations without knowing the theoretical principles of genetics.They had learnt how way to achieve this by trial and error.The basic idea was selection.This means that farmers select in a population individuals with an aberrant or superior trait, and use them for preferential breeding in the next generation(s).If the superior trait continued to be present in the progeny, it may have been hereditary: a mutant.That practice was repeated again and again over the centuries.Mutations were known, in particular in plants, but occasionally in animals as well (Fig. 2).Collecting and selecting mutant tulips, begonias, azaleas, roses, lilies and even orchids was a commercial business in the early 1900s in the immediate neighbourhood of the farm where I grew up.And selecting pigeons was practiced by numerous pigeon fanciers, as mentioned in Darwin's On the Origin of Species (1859).Selection methods that were common practice in farming for centuries may have been new to the young Charles Darwin.
Thus there was a dichotomy: some biologists continued teaching biology in the classical way, namely by focusing on systematic biology, and continuing to label biology as a mainly descriptive discipline.Darwin and Linnaeus saw the variability (similarities and differences) in morphology and anatomy, and used it for designing a classification system.It was Darwin, Lamarck and others who made the link with evolution: the birth of the common descent idea.That was the type of biology I A. De Loof J Physiol 602.11 grew up with: learn the names of phyla, families, species, all in Latin: rather boring.Modern (molecular) biology (see next) was not yet covered in Introductory Biologynot even in genetics textbooks.I became more interested in how organisms living in very different environments function, and how they could cope with challenges, e.g.toxins, viruses, etc.Briefly, my interest in evolutionary biology was not at all triggered by any of my (older) professors at the university.It was the arrival of a new generation of very young professors who had been trained as postdocs in the USA who started teaching the New Biology centred on the principles of molecular biology.They opened a new world to the 'homestayers' .Genetic theory, variability, mutations and the selection practices of farmers and growers were finally put on a logical, understandable basis.They explained that what farmers and horticulturists had been doing for centuries in their selection efforts was correct, and could be continued.These practices are still in use today.
1970: the caesura before and after the Central Dogma that changed biology dramatically and permanently: DNA→RNA→proteins While teaching biology 'the classical way' continued up to the 1970s-1980s (it takes time to prepare new editions of textbooks, and to have professors accept them), novel insights for an alternative approach of genetics-related topics were developed in a few laboratories from the 1950s onwards.In particular two epoch-making papers outlined the new principles: one by Watson & Crick (1953) and the other by Crick (1970) (Maurice Wilkins and Rosalind Franklin deserve to be quoted, as well, as pioneers in bringing up the new ideas).What makes the Central Dogma (Fig. 3) so innovative is its level of correctness at a time when genome research was only just beginning.The Central Dogma of genetics does not describe the mechanics of protein synthesis but tells us that gene expression follows a near-predictable pattern.These papers and many additional ones marked the beginning of the era of molecular biology.Concurrently, the introduction of electron microscopy, of advanced tools for studying biochemistry and of some wording and methods from the computer sciences was very beneficial for the discipline of cell biology.In its turn, this discipline gave a boost to physiological research, making it into a major tool in broadening the theory of evolution.
The molecular genetics approach answered many open questions.Books on molecular biology rather quickly replaced the classical genetics textbooks.New editions of introductory biology textbooks got chapters introducing the principles of modern molecular biology.Research Two examples: left: tulip mutants that were selected and then mass-cultivated over centuries.Remember the tulip-mania and the stock market crash (early to mid-1600s in Holland).Right: a cattle mutant with hypertrophied muscle development due to a mutation in the 'dikbil allele', which was brought to large-scale commercial exploitation in some West European countries.For example, the Belgian White-Blue is a breed of beef cattle from Belgium.The extreme muscle development is caused by an 11-base-pair deletion in the myostatin gene, which leads to some loss of its normal function which is inhibition of hypergrowth (see Wikipedia, 'Belgian Blue' and 'Double-muscled cattle').The tulip picture: from Jan Pereboom (The Netherlands), who published numerous pictures of flowers on his website 'Collection: Flowers' (flickr.com),licensed under CC BY-SA, Open Access.The bull picture: licensed under CC BY-SA from Wikipedia, also Open Access.

Figure 3. The Central Dogma
Left: the 'Central Dogma according to F. Crick (1970).Google Pictures, Biology Dictionary.netEditors, "Central Dogma" Open Access.For more text, see Knapp (2021).Right: it yielded a wealth of novel insights for genetics and evolution theory.
fund-granting agencies reoriented some of their interests towards the molecular approaches.In retrospect, in the past half century since 1970, biology metamorphosed from being an almost fully descriptive discipline into one with basic principles as solid as the ones in chemistry and physics: biology reached maturity.Some authors warned of over-interpretation (e.g.Noble, 2018Noble, , 2022)).
The Modern Synthesis and its extensions: splendid theory but still insufficiently all-round The Modern Synthesis incorporates many complementary approaches.As important as they are (Barton, 2022; see Wikipedia, 'Modern synthesis'), this paper does not focus on any genetic aspect of classical evolutionary theory that might still need some upgrade: I leave this to the numerous specialists who are active in this field.The shortcomings I have in mind concern the larger knowledge gaps, e.g. in the importance of communication activity as a major driving force of evolution, and in the acceptance of a triple memory system instead of a single (genetic) one.Another goal is to formulate a concept/paradigm with wording that better incorporates the specificities of the digital era we live in and that is easy to teach.

The answer to 'what exactly is life?' did not readily emerge from the Central Dogma nor from molecular genetics. What was missing?
While some researchers thought, or at least hoped, that after the physics approach of Erwin Schrödinger (1944) had failed to do so, the Central Dogma would come close enough to uncover life's very nature.It did not, or least not readily.In 2002, 32 years after Crick's paper (1970), Koshland, at that time the Editor-in-Chief of Science, published a short paper entitled 'The seven pillars of life' (Fig. 4) in which he outlined the way in which the majority of biologists were teaching an answer to 'what is life?' , namely by listing the major characteristics of living matter and comparing them with those of non-living matter.Next, he tried to distil the integrative concept that emerges by combining them.Koshland thought that reproduction would be a plausible, yet incomplete answer.The counterargument would be: are non-reproducers not yet or no longer alive?Even in combination with the Central Dogma and the laws of genetics, reproductive activity cannot possibly be the right answer.

Missing: a new (computer-era) vocabulary: hardware, software, information, communication, etc
In the absence of appropriate wording/vocabulary, elaboration and propagation of new insights is very difficult, not to say almost impossible.This is clearly illustrated in the 'exploding' disciplines of electronics, computer technology, informatics, the various disciplines in the humanities, etc., all of which were accompanied by the introduction of a novel vocabulary.In the biological sciences a similar development took place after elucidating the basics of molecular cell biology, ecology, etc.Some new computer/digital era terminology (e.g.hardware, software, transfer of information, etc.) has already become part-and-parcel of the daily vocabulary of our children and students.This turned out to be useful in the biological sciences as well.It made it easier to word new concepts that could not yet be adequately described.A, for a long time it was thought that the most appropriate way to approximate life's very nature was to list the major features of living matter.Koshland (2002) visualized this in the form of a temple with seven pillars.In this classical approach reproduction featured as the major outcome of the interactions among all seven pillars.However, according to Koshland (2002) himself, life cannot be defined in full this way.Modified after De Loof (2015a) (Own work, Open Access).B, an artist's representation of the ultrastructure of a eukaryotic cell Also modified after De Loof (2015a) (Open Access).The focus is on the cell organelles that participate in the coding and synthesis of proteins.The 'electric dimension of cells' was not yet considered.
A. De Loof J Physiol 602.11It may not be superfluous to list here some definitions of newer concepts.The reason is that some concepts may have different meanings in the various disciplines they are used in.My way of formulating definitions is evidently influenced by my background.For me, 'life' is mainly written in the language of biochemistry and bioelectricity, not in that of mathematics. Communication.
Communication is transfer of information.This necessitates that we define 'information' .
Communicating compartment.A major goal of this paper is to outline that different levels of organization as well as the fact that 'each bird sings its own song' are, despite all the differences, only variants of one universal unit.A biological compartment -or simply compartment -is a unit based on carbon chemistry and on electricity carried by inorganic ions.This unit is limited by a moderately leaky boundary with appropriate 'holes'; it can stockpile the right form(s) and amounts of energy; and it can generate gradients that can be used for communication to enable the compartment to function from its lowest to its highest levels of compartmental organization (see later).Its basis structure is the sender-receiver.The sender-receiver incorporates automatically gradients (situations of higher to lower), which are omnipresent in living entities (e.g. in development).Feedback is very common in communicating compartments.Feedback is not circular but spiral-like (Fig. 5).
Information.In my early career, it took me quite a while to find a plausible definition of 'information' .The problem was that the numerous definitions were (and still are) are mostly discipline-specific (see Wikipedia for the many aspects of 'information').In my own university, I had quite some discussions with colleagues from our Physics, Philosophy and Communication Sciences departments.I learned that there are nearly as many definitions as specialists.In other words, there does not seem to be a definition that everybody agrees upon.One such definition that was communicated to me by a colleague was the following: ' A message contains information if, upon decoding, it decreases the degree of uncertainty in the system' .This can be a workable definition in physics, but it is not practical in biology, because it is not evident how to quantify the degree of uncertainty.A workable definition for biology of 'information' could be: A message contains information when upon decoding the receiver starts mobilizing sooner or later part of its stockpiled energy to engage in some sort of work; the transport of information through a communication channel (water, blood, air, etc.) usually needs a material carrier.Can information be immaterial?In biology, absence of something can, under specific conditions, be information.In physics, information always has a material aspect De Loof (2015a).
Bioelectricity.A very recent formulation by Pio-Lopez and Levin (2023) reads: 'Developmental bioelectricity refers to signalling among non-excitable cells mediated Their interactions enable communication-problem-solving activity as a key outcome.B, the major centralizing idea is that all types of communicating compartments are organized as senders-receivers with the (prokaryotic) cell as the smallest type.C, in case of feedback, communication is not fully circular, but a unidirectional spiral-like (helical) process.Bifurcation point: at increasing complexity more than one solution for a given problem becomes possible.B, in this approach, in fully organic chemistry based-compartments the sender-receiver communicating compartment with its three memory systems (this paper) is the basic unit of structure, with the (prokaryotic) cell as its smallest representative (see later, by endogenous electric fields and differences in resting potential.These electric states arise due to specific ion channels and pump proteins, which uphold voltage gradients across the cell membrane.Such gradients elicit various cellular responses, including transcriptional and epigenetic responses.'According to Levin (2023a, b) 'Evolution was using bioelectric signalling long before neurons and muscles appeared, to solve the problem of creating and repairing complex bodies.'Software (biological).According to Pio-Lopez & Levin (2023), bioelectricity is the software of life.
Time.Again, there are as many different definitions as there are authors.Even the brightest scientists had trouble with its definition.Life is an activity at a given moment.In its functioning it consumes energy.Thus it can be viewed from the point of view of an energy converting system.This means that to make the symbolic notation of life (De Loof, 2016) more complete, the time dimension too should be defined and added, not a simple task.I used a burning candle as a simple experimental model of an energy-converting system in trying to uncover under what conditions 'time' has a meaning.The definition that I tried to formulate reads: Time (t) as experienced in daily life (to distinguish it from Newton's absolute time which applies to the scale of stars and the universe (T)) could, perhaps, be defined as the inertia by which in a given energy-converting system, one form(s) of energy is converted into one or more other form(s) plus change in entropy.
During the past half century, the number of new words in use in biology has hugely increased, making keeping up with all the novelties hardly possible, a major problem for teaching.It facilitates explaining why organic and cultural evolution (De Loof and Vanden Broeck, 1995;De Loof, 2015b) are the two sides of the very same coin, and why cells also must have, in addition to their genetic/hardware memory, also a learning/software memory, and an electric memory that is essential for their functioning as 'miniature electrophoresis chambers' (see below).6), thought to have been accidentally imported from its native habitat somewhere in the Rocky Mountains (USA), had not landed in Europe and begun destroying potato fields.Panic all round: schoolchildren were sent into the potato fields to search for, collect and destroy the typically yellow-orange egg pods that they found at the bottom of the leaves.This primitive attempt to control the rapidly spreading plague was hopelessly inadequate.
The plant protection industry as well as laboratories in entomological research centres and in universities could not provide a rapid cure.Professor de Wilde was doing research, among other topics, on the Colorado potato beetle and on locusts (another major plague insect in warmer countries).He was interested in the question whether, perhaps, an insect hormone known as juvenile hormone (JH), of which several physiological effects were already known but not its chemical structure, could become an environment-friendly insecticide against the Colorado potato beetle and other insects.Worldwide, research teams were engaged in identifying JH, a real challenge.De Wilde's lab was specialized in physiology, but it did not have the very expensive tools for purifying and chemically identifying JH.Some laboratories in the USA had that sort equipment and succeeded: de Wilde had good contacts with them.To cut a long story short, I became a member of the JH research sub-team.On my arrival, my expertise in endocrinology was almost non-existent.It meant that I had to learn everything from zero, a fortunate challenge, because I could think freely, without the ballast of already existing and sometimes wrong hypotheses.To summarize the way of thinking in comparative endocrinology in the late 1960s: insects and other arthropods were thought to be primitive animals totally different in physiology from vertebrates (mammals and fish, the at that time current models), worms, etc.If simple animals like insects would have hormones, an idea rejected by quite some researchers, these hormones would be very few and, for sure, very different from the ones already identified in higher vertebrates.I disagreed with this view, which was against the common descent principle of Darwinism.Furthermore, there was no reason to assume that control of the activity of the various organ systems would need less complex hormonal control systems in smaller than in larger animals.But what was missing to prove who was right?The comparison of invertebrates versus vertebrates of the amino acid sequences and coding genes of neuropeptidic hormones.In my later life, my laboratory spent decades in helping to fill this gap in knowledge in insects/arthropods, while other laboratories did so for molluscs, echinoderms, Caenorhabditis elegans, etc.
A major breakthrough: the structure of molluscan and other invertebrate insulins strongly resembles human insulin.Insulin was the first peptide hormone discovered.It was isolated from dog pancreas in 1921 (by Banting and Best), but it took until 1951 before its amino acid structure could be fully sequenced by Sanger.It turned out to be a heterodimer of an A-chain and a B-chain, which are linked together by disulfide bonds (Fig. 7).The molecular origins of insulin-like proteins go back at least as far as the simplest unicellular eukaryotes, and thus over 1 billion years.Apart from animals, insulin-like proteins are also known to exist in fungi and protists, and to play a role in various physiological systems (see Wikipedia, 'Insulin').In Europe, the laboratory of Prof. Joos Joosse in Amsterdam, which studied among other topics, the neuroendocrine system of the snail Lymnea stagnalis, reported that growth-controlling molluscan neurons produce the precursor of an insulin-related peptide (Smit et al. 1988).The similarity with already known mammalian insulins, the human one included, was striking.
Similar discoveries were made in other molluscs as well (Okamoto, 2021), and in other invertebrates (Elphick et al. 2018; and many other research teams), insects included.Of particular interest in comparative endocrinology is the finding that in the silkworm (Bombyx mori), one of the two brain secretory peptides (Prothoracicotropic Hormone (PTTH) and bombyxin), is insulin-like.Bombyxin plays a role in controlling moulting and metamorphosis.It is a 5 kDa heterodimeric peptide that is synthesized by eight dorsomedial neurosecretory cells of the brain, and shows a high similarity to insulin in both its amino acid sequence and its coding gene structure (Ishizaki & Suzuki, 1994).Remarkably, the Bombyx genome contains the exceptionally high number of more than 30 copies of the bombyxin gene.In retrospect, the enormous advances in technology for identifying neuropeptides enabled such rapid progress that one after the other the known neuropeptides (and their receptors) of vertebrates were almost all shown to have a structurally similar counterpart in invertebrates, and vice versa.All this made clear that the validity of the common descent principle could no longer be denied.

State of the art to date?
The endocrine systems of all animals have so many things in common that it has become common practice to include Drosophila, Caenorhabditis elegans, annelids, echinoderms, etc. as models in basic research in vertebrate endocrinology, both general and medical.The similarities between the endocrine systems of invertebrates and vertebrates largely outnumber the differences.Furthermore, it became very clear that small invertebrate organisms have neither fewer endocrine signalling pathways nor fewer ligand-receptor pairs than larger ones.A striking example: the tiny worm C. elegans, the only organism to have its whole connectome (neuronal wiring diagram) elucidated, has only 302 neurons in its whole body while humans have while humans have billions (8.6 × 10 10 ) (see Wikipedia, 'List of animals by number of neurons').Beets et al. (2022) undertook the construction of a system-wide mapping of neuropeptide-G-protein-coupled receptor (GPCR) interactions in this small but not at all simple worm.By reverse pharmacology screening of over 55,384 possible interactions, they identified no fewer than 461 cognate peptide-GPCR couples, uncovering a broad signalling network.C. elegans has become a promising model for studying the role of neuropeptides in non-associative and associative learning as well as in forgetting (Frooninckx et al., 2012;De Fruyt et al., 2020;Van Damme et al., 2021).

Electrical effects of hormones: an unexpected (and still undervalued) novel insight: the cell as a miniature electrophoresis chamber
Since the 1960s the main focus in comparative endocrinology has been on the identification of novel hormones and their receptors.The search for their mode of action also continued.A truly novel mode of action was discovered by Woodruff & Telfer (1980) while studying the development of the ovaries in silk moth (Hyalophora cecropia).This insect has polytrophic oocytes, which means that during yolk deposition the growing oocyte remains connected -through cytoplasmic bridges -with seven sister cells, called nurse cells.They deliver RNA to the oocyte in a polarized way, namely exclusively from the nurse cells to the oocyte without any flowback.Using ingenious techniques, the researchers proved that this unidirectional transport very much resembled the charge-dependent migration of proteins during electrophoresis in laboratory equipment.
That stimulated thinking on the nature and function of biological electricity in organ systems other than the already studied nervous and muscular systems.Electrical current means transport of charge.The current from the electrical socket is carried by electrons; biological electrical current is carried by inorganic ions in particular H + , Na + , K + , Ca 2+ and Cl − .A challenging question was how a self-generated inorganic-ion-based electric current could flow from A to B. Further analysis of the system resulted in the concept of 'self-electrophoresis' , closed current loops, and emphasis on generating a non-spherical (asymmetrical) distribution of ion pumps and ion channels over the plasma membrane of cells.In a watery environment extracellular electric fields, which are omnipresent in animals, plants, fungi, etc., can be measured by the vibrating probe technique (Jaffe & Nuccitelli, 1974).It also led to the insight that all cells have a self-generated electrical dimension, which is essential to being alive: death ensues if it comes to an irreversible standstill.Thus, since the origin of the very first ancestral cell, the electrical activity had to keep going on: cells have an electrical memory that never, ever stops, not even at cell division.It thus functions on its own, partially independent from the Central Dogma (see later) (for more details see De Loof, 1986Loof, , 2016)).Hitherto the electrical dimension has hardly been taken into account in established theories of evolution.
In classical biology, with respect to (cellular) memory, nearly all focus is on the genetic memory system with the Central Dogma at its very heart.But some types of organisms, in particular animals, also have a cognitive memory system (some even without having a head or brain; Baluška & Levin, 2016) of which the underlying biochemical and biophysical mechanisms are still only partially understood.Thanks to the great progress that has been made in the humanities, the ways it can be used and guided are increasingly better understood.Biological electric current is carried by inorganic ions (De Loof, 1986, 2016).Ion pumps and channels are to some extent non-symmetrically distributed over the plasma membrane.In such case, cells have the potential to drive an ionic/electric current through themselves (white arrows in Fig. 8A), thereby becoming (temporary) miniature electrophoresis chambers (Fig. 8A).The electric properties of cells do not arise de novo after each cell division.Part of the plasma membrane is shared between parent and daughter cell at cell division (Fig. 8B).Thus, there is an electric memory system that may never irreversibly fall to zero, and this since the very origin of life on earth.As illustrated in Fig. 8C, extracellular electric/ionic currents were measured and visualized by the vibrating probe technique developed by Jaffe & Nuccitelli (1974).
A. De Loof J Physiol 602.11The dual origin of the wording of the novel paradigm.Part 2: evolution of life What conditions should a plausible definition of 'life' meet?In 1978, I was asked to teach an introductory course of general biology in which a topic was: What exactly is life?I felt embarrassed in front of my students that I could not do better than follow the approach that was widely used worldwide in general textbooks: enumerate the list of major properties of 'the living state' , and next conclude that 'life is the total sum of all that' (Fig. 4 as an example).My problem was that, in my opinion, all these properties should fit in a logical, preferably simple concept that, unfortunately, remained unrecognized at that time.When I confronted my students with my problem, some students reacted with 'Why should we take a course of which the subject cannot be defined by the teacher?' and 'Why don't you come up with a good definition yourself?'I accepted the challenge.But to my frustration, I did not manage to come up with a plausible definition before the end of the course… It took me several more years of trial and error to come up with a definition that in my opinion met the criteria of a good definition according to the philosophers Schejter & Agassi (1994).Their wording: ' Apart from its not being trite and uninformative (circular, to use a traditional term), it should be neither too wide nor too narrow; it should not exclude living things and it should not include dead ones.Furthermore, it should not make biology part-and-parcel of chemistry and physics' (meaning that there should be room for an 'immaterial dimension' .I add: it should organize all known dimensions and properties of living matter in a logical order and context, and it should pave the way for defining what exactly happens at the moment of death.Too many conditions to possibly catch in a single comprehensible sentence?No, it can be done (De Loof & Vanden Broeck, 1995;De Loof, 2015a).
By 1990, it became clear that a definition of life was not likely to follow from some principles of physics as Erwin Schrödinger (1944) had advanced (De Loof, 1993), nor from the Central Dogma of biology, as originally worded by Francis Crick (1970) and colleagues.Neither were any of the numerous definitions that were published at that time sufficiently all-round (examples in De Loof (2002).More recently, Villarreal & Witzany (2019) formulated a communication-based definition of life that comes close to mine.
What was missing in all classical approaches?The sender-receiver concept.What could be missing, in particular in Koshland's outline?To make a long story short: the tool or 'machine' that makes the seven pillars, which are all nouns, into an energy-requiring activity, and thus into a verb, namely it enables transfer of information in systems organized as senders-receivers (Fig. 5; De Loof, 2015a).Life itself is not a machine (Witzany & Baluska, 2012;Witzany, 2014Witzany, , 2020)), but the activity that can result from all its ongoing interactions.This concept is not inherent to the Central Dogma, but to the principles of communication activity.This activity is a synonym for transfer of information, a concept that can have different meanings depending on the context or discipline.It was my experimental work in comparative (insects, vertebrates) endocrinology, in which the sender-receiver concept was, and still is, at the very heart, that paved the way towards finding a plausible definition for life as an activity.
Bringing order to the multitude of communicating compartments (sender-receiver types).Major revolutions.It was a real challenge to find a way to uncover the key to 'seeing the wood for the trees' .That became possible after asking the questions: Which type(s) of communicating compartment can die?Only organisms or also other types of organization, e.g. a population, a colony, etc.? And what exactly changes at the very moment of death?To bring order and logic into the multitude of existing compartments, a communication-based classification system was devised (De Loof & Vanden Broeck, 1995;De Loof, 2002).Its essence is depicted in Fig. 9   A. De Loof J Physiol 602.11 the deduction of this and other more accurate symbolic notations that also include the types of chemistry and electricity, see De Loof & Vanden Broeck (1995) and De Loof (2002Loof ( , 2015a)).
Because life is an activity of a given sender-receiver compartment of many different forms (man-made artificial life included), one can further specify the definition and the symbolic notation by taking into account the type of chemistry, electricity, etc.Although it is a sum, the whole is more than the mere mathematical addition of its parts.This is due to the fact that the parts interact in specific ways, and are enabled to do so by the organization of living compartments as senders-receivers.

Communication harbours endless possibilities for evolutionary change and adaptation
Any of the four pillars of life (Figs 4 and 5) is subject to change, and hence an endless number of combinations are possible.
There are three types of memory systems: life as a genetic-cognitive-electrical or in a digital-era formulation, a hardware-software-electrical triple memory continuum, as follows.
Genetic memory with DNA→RNA→protein(s) at its very heart.The major focus of the Modern Synthesis and its extensions is on the possibilities for change of this memory type.In principle genes last lifelong.Genes can mutate in a variety of ways or change epigenetically.Changes in gene frequency (in populations) are most important in the long run.
Cognitive/learning memory, of particular interest to short-term learning and to cultural evolution.This memory acts instantly.The speed at which this type of memory operates is so fast that it most probably operates largely electrically, and thus by the help of inorganic ions.Its molecular as well as its electrical mode of action continues to be poorly understood.Important for physiology, the cognitive memory also harbours the possibility to forget, in particular lots of irrelevant information.Selective forgetting is a means of brain protection.
Electric memory: the 'electrome of cells' (De Loof, 2016Loof, , 2022)), which is absolutely vital to being alive, for functioning of epithelia, the nervous and muscular systems, osmoregulation, self-electrophoresis, some roles of the cytoskeleton, etc.In introductory textbooks of biology, it is seldom mentioned that the electrical dimension of cells does not arise de novo at each cell division.It is shared between parent and daughter cells.
There are three possible types of types of progeny as well: physical children/descendants; learners/pupils/forgetters; and 'electricians' (more explanation in De Loof, 2022).

The important relationship between communication activity and problem-solving
Problem-solving activity: at the very heart of adaptation.
' Adaptation concerns the solving of a particular (set of) problem(s) in a given environment/context, making use of preexisting problem-solving strategies' (De Loof, 2004).'Survival of the fittest' says nothing more than that the survivors survive.An alternative could be: 'if they are not prematurely eliminated by accidental death, the best problem-solvers have better chances for being rewarded with a higher level of contentment (see 4th pillar of life in Fig. 5), and by faster growth and reproductive advantages' .Problem-solving requires adequate hardware, software, energy as well as the proper motivation (motivational salience: De Loof, 2022).
Any act of communication is a problem-solving act.The enabling role of communication follows, in part, from the fact that any act of communication is a problem-solving act.Indeed, any message is coded and needs to be decoded at its arrival at a target that has matching receptors.Idem for responding to the decoded message(s) sooner or later.This means that problem-solving is inherent to communication, and thus to life itself.No life without problem-solving.Problem-solving needs the presence of appropriate memory systems in which the decoding programs have to be stockpiled in advance.
Selection passively follows the preceding (un)successful problem-solving activity.The best problem-solvers survive: they have better chances for making it to the reproductive stage and having a fertile progeny.Problem-solving implies self-selection.
Life itself as the driving force of its own evolution: false or correct?Is this Bergson's (1907) 'vital force'?If it is correct that evolution is driven by the 'communication drive' with its inherent link to problem-solving as suggested for the first time almost two and a half decades ago (De Loof & Vanden Broeck, 1995), it actually means that life is its own driving force resulting in self-selection (De Loof, 2016, 2022).This results from the following reasoning: if life is communication activity and if communication activity drives evolution, it then follows that life drives its own evolution.Thus, life cannot exist without evolving.
Life (as an activity) is an approximating synonym for communication activity.
Through its inherent link with problem-solving, changes in communication drive evolution.
Thus, life drives its own evolution.At first sight this looks like a circular deduction, and thus false.But is it circular?If feedback mechanisms were perfectly circular, which means that upon being repeated two or more times not the slightest change could be observed, neither in the words nor in the intonation (whatever their nature) used in a conversation, there would be no evolution as no changes would occur.But as stated before, feedback loops are not perfectly identical, but slightly different, and thus they are spiral-like with the possibility of encountering bifurcation points (Fig. 5C).For a definition of a bifurcation point see Fig. 5.In fact life as the driving force of its own evolution is a most ingenious, splendid mechanism that always works.
A flash back: the French author and philosopher Henri Bergson (1859Bergson ( -1941) ) was famous because he won the Nobel Prize for Literature, in part because of his partially anti-Darwinian ideas about evolution, and his ideas about the nature of time.He advocated the existence of a 'vital force' (Bergson 1907).He never uncovered its very nature.My interpretation: Bergson's 'vital force' is probably nothing but communication/problem-solving activity, and thus life itself.In Bergson's lifetime, neither the exact sciences nor the humanities were advanced enough to arrive at such an explanation.
Organic and cultural evolution are the respective hardware-software sides of the same coin This topic has been dealt with at length in De Loof (2015b), and in the following abbreviated version (taken from De Loof, 2022).The integration of cultural evolution into classical neo-Darwinism has been problematic.This follows from the idea that cells have only one memory system with the Central Dogma at its very heart.Later, it was thought that additions/extensions could yield a sufficiently integrative concept.These approaches, too (e.g.Gould, 2002), tended to overlook that cells have three memory systems: genetic, cognitive and electrical.In cultural evolution the cognitive memory system and teaching-learning are of prime importance.It mainly acts the 'Lamarckian' way.The electrical memory system likely is part of the cognitive memory system (Levin (2023a).It is based upon inorganic ion effects and hence does not in full depend upon the Central Dogma.The cognitive memory remains a black box, and although we still do not understand its full functioning we should still take into account its importance.The humanities have amply shown how this can successfully be realized.My approach: consider life as a hardware-software continuum with an extra electrical dimension, and wait until a second Central Dogma (governing the cognitive memory) will be formulated: this may take quite some time.Also keep in mind that some biological problems are solved the hardware way (Darwinian organic evolution), others the software way (Lamarckian cultural evolution).

Limitations of current research and future directions
In my opinion, the truly major challenge for the future is the unravelling of the mode of action of the cognitive memory system.Despite intensive research worldwide, progress is slow (Reber et al., 2023).It can be expected that in due course, hopefully in the near rather than in the distant future, a second central dogma that governs the cognitive memory system will be formulated.Another remaining challenge is the further unravelling of the role of the cytoskeleton in transport of self-generated cellular electricity.This type of electricity is carried by inorganic ions.

Final conclusion
This paper summarizes how over a time span of some 50 years, bit by bit, it became clear that classical Darwinian evolutionary theory, with its major focus on genetic mechanisms that are causal to generating variability instrumental to evolutionary change, undeniably needs both a 'software' and an 'electrical' upgrade.The way to implement such upgrades proved to be rather simple and logical.It started from the principles of communication with their already very widely used computer-era wording that fits our young students like a second skin: handling of information, sender-receiver, coding-decoding, problem-solving, hardware-software, etc.A major consequence is that the main focus of evolutionary theory is no longer: how do new species come into existence?It shifts more and more towards: how does communication activity with its inherent link to problem-solving change over time?This approach strengthens the link between the exact sciences and the humanities with communication as their common interest.
Two catchy one-liners that may remind students of the complexity and ingenuity of evolution: Living systems are self-electrifying, communicating (= transferring information), working, reproducing and incessantly changing aggregates of fossil stardust, which all have in common their sender-receiver type organization: each of them a wonder of ingenuity.
In the recent past I repeatedly stated that, paraphrasing Theodosius Dobzhansky (Ayala, 1977;Shapiro, 2016): Nothing in biology and evolutionary theory makes sense except in the light of the ability of living matter to communicate, and by doing so, to solve problems both the hardware and the software way.

Figure 1 .
Figure 1.The development the communication-based paradigm was a multi-step process over a period of about 55 yearsThe communication/problem-solving approach may be a valuable alternative to the classical genetics-approach of neo-Darwinism.Parts of the novel paradigm have been published previously.

Figure 2 .
Figure 2. Farmers practiced selection already centuries before Crick's publication of the Central DogmaTwo examples: left: tulip mutants that were selected and then mass-cultivated over centuries.Remember the tulip-mania and the stock market crash (early to mid-1600s in Holland).Right: a cattle mutant with hypertrophied muscle development due to a mutation in the 'dikbil allele', which was brought to large-scale commercial exploitation in some West European countries.For example, the Belgian White-Blue is a breed of beef cattle from Belgium.The extreme muscle development is caused by an 11-base-pair deletion in the myostatin gene, which leads to some loss of its normal function which is inhibition of hypergrowth (see Wikipedia, 'Belgian Blue' and 'Double-muscled cattle').The tulip picture: from Jan Pereboom (The Netherlands), who published numerous pictures of flowers on his website 'Collection: Flowers' (flickr.com),licensed under CC BY-SA, Open Access.The bull picture: licensed under CC BY-SA from Wikipedia, also Open Access.

Figure 4 .
Figure 4. What was 'life' in the pre-digital era?A, for a long time it was thought that the most appropriate way to approximate life's very nature was to list the major features of living matter.Koshland (2002) visualized this in the form of a temple with seven pillars.In this classical approach reproduction featured as the major outcome of the interactions among all seven pillars.However, according toKoshland (2002) himself, life cannot be defined in full this way.Modified after De Loof (2015a) (Own work, Open Access).B, an artist's representation of the ultrastructure of a eukaryotic cell Also modified after De Loof (2015a) (Open Access).The focus is on the cell organelles that participate in the coding and synthesis of proteins.The 'electric dimension of cells' was not yet considered.

Figure 5 .
Figure 5.What is life in the computer/digital era?A, the temple here has only four pillars.They are all subject to change and therefore possible sources of variability.Their interactions enable communication-problem-solving activity as a key outcome.B, the major centralizing idea is that all types of communicating compartments are organized as senders-receivers with the (prokaryotic) cell as the smallest type.C, in case of feedback, communication is not fully circular, but a unidirectional spiral-like (helical) process.Bifurcation point: at increasing complexity more than one solution for a given problem becomes possible.B, in this approach, in fully organic chemistry based-compartments the sender-receiver communicating compartment with its three memory systems (this paper) is the basic unit of structure, with the (prokaryotic) cell as its smallest representative (see later, Fig.9).More details in DeLoof (2022).A-C reproduced from De Loof (2015a, c); all own work and open access.
Figure 5.What is life in the computer/digital era?A, the temple here has only four pillars.They are all subject to change and therefore possible sources of variability.Their interactions enable communication-problem-solving activity as a key outcome.B, the major centralizing idea is that all types of communicating compartments are organized as senders-receivers with the (prokaryotic) cell as the smallest type.C, in case of feedback, communication is not fully circular, but a unidirectional spiral-like (helical) process.Bifurcation point: at increasing complexity more than one solution for a given problem becomes possible.B, in this approach, in fully organic chemistry based-compartments the sender-receiver communicating compartment with its three memory systems (this paper) is the basic unit of structure, with the (prokaryotic) cell as its smallest representative (see later, Fig.9).More details in DeLoof (2022).A-C reproduced from De Loof (2015a, c); all own work and open access.
versus vertebrates.I would never have become interested in thinking about major mechanisms causal to evolutionary change if I had not had the opportunity to join the Laboratory of Entomology in Wageningen, The Netherlands (at that time the Valhalla for comparative endocrinology in Europe), for doing most of the experimental work for my PhD degree under the supervision of Professor Jan de Wilde.Nor if an exotic insect, the Colorado potato beetle (Leptinotarsa decemlineata Say) (Fig.

Figure 7 .
Figure 7.The search for insulin-like proteins and for other hormone families, in particular of peptides, which had members in both vertebrates and invertebrates boosted the acceptance of the common descent idea, at least for animals A, the Rhinoceros mammal-beetle picture (by Julie Puttemans, an employee with artistic skills in my former laboratory; open access) served as an emblem for an International Conference of European Comparative Endocrinologists (held in Leuven in 1990).It helped to lower, not to say to overrule, the skepticism against the common descent principle.B, insulin.From Google Images: maker: Tetiana Kovalenko, source: 123RF.

Figure 8 .
Figure 8.The cell's electrome and the sharing of the electric memory system at cell division Parts of this figure are reproduced from DeLoof (1986Loof ( , 2015cLoof ( , 2016)); all are own work and open access.

A
definition of life that meets all criteria listed by Schetjer & Agassi (1994).A logically deduced, unambiguous definition of life (as an activity) reads: 'Life' sounds like a noun (in English, for example), but it denotes an activity, making it more like a verb.What we call life (L) is nothing other than the total sum ( ) of all acts of communication (C) exerted by a given sender-receiver compartment at moment t, at all levels of its compartmental organization (cell organelle, cell, tissue, & whole organism, & population, community, Gaia level).The simplest symbolic notation reads: L = C.For

Figure 9 .
Figure 9.A possible classification system for bringing some order in the complexity of the variability of the many levels of compartmental organization (left side), and the means for generating daughter compartments (right side) This only aims at providing a glimpse of the huge number of different languages/signalling pathways/problem-solving strategies that are incessantly used in nature.For more explanation, see legend in De Loof 2002.This two-dimensional representation of the succession of levels does not mean that such evolution is linear by necessity: it is not.The different levels represent major revolutions in evolutionary history (De Loof, 2002).This figure is reproduced from De Loof & Vanden Broeck (1995) and De Loof (2022); own work and open access.

cited definitions in mind, death and life can be plausibly defined Death: the very nature of death of any communicating compartment or level. Death
With the