The Evolution of Perception

C. Cristofre Martin
Department of Anatomy & Cell Biology, University of Saskatchewan
107 Wiggins Road
Saskatoon SK S7N 5E5, Canada
Phone: (306) 966-4087, Fax: (306) 966-4298
E-mail: cristofre@home.com

Richard Gordon
Departments of Radiology and Electrical & Computer Engineering
University of Manitoba, Health Sciences Centre
820 Sherbrook Street, Winnipeg, MB R3A 1R9 Canada
Phone: (204) 789-3828, Fax: (204) 787-2080
E-mail: GordonR@cc.UManitoba.ca

Martin, C.C. & R. Gordon (2000b). The evolution of perception. Cybernetics & Systems, submitted June 7, 2000.

ABSTRACT: "Perception" has been invoked as the explanation of specific interactions of everything from electrons to humans. While this may or may not be a misuse of the word, we are attempting to tie all levels together by a careful consideration of how perception has evolved. We start with the rich perceptual abilities of bacteria and Protoctista. From this middle vantage point, we hope to piece together how perceptual abilities evolved from the atomic and molecular levels, and define the problems in explaining how multicellular eukaryotes evolved even greater perceptual capacities.

Whither Reductionism? As humans it is easy for us to describe our perception of the surrounding universe because within us the act of perception, along with providing important information for our survival, invokes very strong behavioral and emotional responses. Our perceptual system is our bridge between the internal and the external universe. Thus perception creates our universe and is the essence of our humanity.

We would have liked to embark on a study of the evolution of perception that begins from a nonperceiving world and shows how perception arises as an emergent phenomenon (Hall, 1969). So we turned to basic physics, and were surprised and dismayed by its current state. In the Copenhagen interpretation of quantum mechanics, an act of conscious observation seemed to be needed to collapse a wave function to get a discrete event. This leads to worries about whether the world exists without an observer, and questions about just how intelligent that observer has to be. Fortunately, contradictions of the Copenhagen interpretation have been found, and a plethora of alternate interpretations discussed (Healey 1989; Gribbin 1995). Some of these are consistent with removal of the observer from the essence of quantum mechanics. These new ideas bring in multiple universes, instantaneous action at a distance, and waves that travel backwards in time, seemingly outlandish concepts that become somewhat reasonable in the context of the theory of relativity. At least we can start to believe that the universe did exist in some sense before there was anyone or anything to perceive it, and that it did have a history of sorts before life appeared.

Grössing (2000) has thrown a monkey wrench into our hopes of separating perception from the physics of even elementary particles. He comes to an interesting set of conclusions:

1. Perhaps there is an ether after all, but it is four dimensional (he calls it aether).
2. So called elementary particles may be just nonlinear waves in the aether.
3. Particles may actually be a pair of waves, one that travels slower than the speed of light, say at v < c, and one that travels faster, at u > c, so that uv = c2.
4. The faster, superluminal wave, may be of such a huge extent that atoms can hardly be regarded as discrete objects.
5. An observer need not be invoked to resolve the states of a quantum mechanical system.
6. An elementary particle may have a complex structure, of size between 10?33 to 10?16 cm.
7. That structure might accommodate a cybernetic arrangement of circularly causal interactions between the subluminal and superluminal waves.
8. This interaction can be described in terms of the particle (the nonlinear portion of the subluminal wave) "perceiving" its environment via its superluminal wave, which responds to the rest of the universe.

All of this physics is very curious, and makes the life of a biology reductionist somewhat difficult. As reductionists (§1.14 in Gordon, 1999) we prefer to use physics rather than science in general in arguing the reductionist point of view, because physics is (rightly or wrongly) regarded as the fundamental science, and in the reductionist point of view that is where we start. Many scientists, in working on higher level problems, postulate additions to science that may or may not be explicable in terms of physics itself (cf. Vrba & Eldredge, 1983; Bock & Goode, 1998).

Science, Religion and Perception: Science and religion begin at opposite ends in explaining the universe. Physics starts from what a mathematician would call primitives and axioms, and attempts to build up towards explanation of ever more complex phenomena, hoping someday to explain awareness and consciousness. Religion takes an omniscient awareness as its starting point for creation. Most scientists avoid religion, at least in their science, as either irrelevant or inexplicable. Neither attitude is particularly worthy of science, for either religious phenomena are dismissed rather than being investigated, or no attempt is made to approach them in the spirit of scientific enquiry. The exceptions hardly explain life (Davies, 1992). The common, everyday phenomenon that most of us can agree on as unexplained is our consciousness. Three basic positions have developed in the debate over the past 2500 years (Hall, 1969):

· Do "lower" organisms or even inanimate matter (let alone artificial intelligence) share in consciousness?
· Is consciousness a fragment of some higher awareness?
· Or is it an emergent phenomenon?

While much has been written on consciousness, no explanation fits into our current paradigms. From a reductionist point of view, the evolution of perception would seem to precede the evolution of consciousness. Furthermore, it is worth noting that some high order perceptual abilities can operate without consciousness (Schacter, 1992). Perhaps a better understanding of the evolution of perception might someday provide a foundation for understanding the evolution of consciousness (cf. Cairns-Smith, 1996).

In a way, physics explains nothing. It deals with interactions between point objects and fields, all of which are either taken as given, or explained in terms of smaller point objects and fields. (The exception may be strings, about 10?33 cm in length: Schwartz, 1998.) To get any further than that, to talk about rocks and stars and galaxies, let alone life, we claim requires acts of perception. This is a rather peculiar situation, because perception (for now) occurs in living organisms, which are part of what we are trying to explain. It is for this reason that we take the tact that what we actually need to explain is the origin and evolution of perception. "The problem of getting the knower into the picture has become acute now that most of us have become convinced that the knower is itself a physical system" (Bridgman, 1959). The knower gets into the picture through evolution.

How does a perceiving universe build itself? Perhaps the bridge between physics and God is the perceptogenesis of the universe, indeed, through life (where most perception would seem to occur) and thus through us. In a sloppy language molecular biologists often speak of molecules "recognizing" one another, of "signal" transduction, of mind and intention at the molecular level (§1.18 in Gordon 1999). We would like to examine perception at every level, below, at and above the molecular level, to see if that sloppiness of molecular biologists contains a germ of truth, perhaps one amenable to a more rigorous analysis.

Perception Alters the Physics that Happens: You perceive a rock as a discrete entity, itself rather heterogeneous, recording some of its cosmic history. But from the point of view of physics, the rock is nothing but a solution to equations whose primitives are particles, waves, and fields. Yet you can alter that rock as a rock. You can change its position, rearrange its atoms with a hammer, or use a polishing wheel to make it into jewelry. Thus your act of perception changes the universe. In fact, it is clear that many acts of perception have altered the surface of the earth considerably, even just considering acts of perception by Homo sapiens. True, H. sapiens has had but this local effect, only beginning to impact on more than one planet, but who knows what lies ahead (cf. Tipler, 1994)? The point is that acts of perception do alter the universe, including altering specifically what is happening down at the level of atoms and electrons and fields.

There is nothing in physics that leads to rocks. The abstraction of a rock from the rest of existence requires an act of perception. There is thus a poverty of physics, here recognized by a physicist, with a hint of evolution of perception indicated:

"The concepts in terms of which we describe and understand the world about us do not occur in nature, but are man made products. Such things as length, or mass, or momentum, or energy occur only in conjunction with brains. The significance of these concepts cannot be isolated and associated only with the external world, but the significance is a joint significance involving external world and brain together. Now it seems to me that it is quite conceivable that different properties of the brain structure are involved in the concept of length, for example, than are involved in the concept of mass. It might be that the concept of mass is beyond the powers of certain simple types of brain whereas the concept of length might be easily within them. If such were the case, or if our present brain structure carries vestiges of limitations of this sort, our outlook might be materially altered" (Bridgman, 1959).

Solve the fundamental equations of physics as much as you want, by vast computer simulations. Never will such a simulation have as its output rock. You might perceive simulated rocks in the output, but that is your perception. Computer programs may imitate our pattern recognition and classification abilities, and label some fraction of a solution to the equations as rock (cf. Weiskrantz, 1985). But the equations of physics themselves will never produce a rock. If not rocks, then not life. If not life, then not consciousness. If not consciousness, then not God. Physics is impoverished, and cannot explain what we want to know. And thus are we driven to grapple with the evolution of perception, for if we are to start with physics, we need to figure out how to ratchet our way up the scale of awareness, from our subatomic beginnings.

Perception in Unicellular Organisms: To work at understanding the evolution of perception, we need a starting point. For this we have chosen unicellular organisms. From here, we can look down through macromolecules to chemical specificity to the peculiar so-called perceptions of atoms and subatomic particles. We can also gain a perspective on the evolution of perception in multicellular organisms, because some abilities need not be re?explained, if they already exist at the single cell level. (A comparable situation may exist in morphogenesis: § 5.05 in Gordon, 1999.)

The evolution of prokaryotic organisms, most of them probably unicellular, involved the past 3.8 billion years. Prior to 1 billion years ago, these organisms had the earth to themselves. In our attempts to make some phylogenetic sense of the extant bacteria, as presumed representatives of their ancestors, we found little or no phylogenetic structure to their perceptual systems. All seemed equally "advanced". (Perhaps this is because eukaryotes preceded prokaryotes, an hypothesis contrary to the common one we entertain here: Penny & Poole, 1999.) We will present what meager evidence we could assemble below. However, another approach is the synthetic one. In this, one could discuss what might be added to current models of the origin of the prokaryotic cell (Erhan, 1977; Matsuno, 1984; Schwemmler, 1985; Fox, 1991) to turn them into perceiving organisms. Most discussion is centred on the origin of the cell, and its novelty as the first "semantic" system (Hoffmeyer, 2000; Vaneechoutte, 2000). We have found no literature addressing the origin of perception. Given that present bacteria are much more social organisms than they have been given credit for (Shapiro & Dworkin, 1997), we might wonder if their perceptual capabilities developed right along with the ability to reproduce.

In order for a population of organisms to survive, the individuals within that population must be able to recognize a suitable living environment (and avoid poor environments), recognize food items, and recognize mates. For an organism to fulfill these tasks it must have the ability to survey the world outside its own body and respond to the information that it receives. That is, the organism must be able to perceive its surroundings and act upon them.

The physical energy received by an organism in an act of perception is far smaller than the energy it puts into responding. In electronics or PCR (polymerization chain reaction) the word amplification means "much more of the same thing". A weak voltage is amplified to a larger voltage. A small amount of DNA is amplified to more of the same kind of DNA. But this is not what happens in perception. At the very first step, a small signal (a few molecules of a particular shape, a few low energy photons, such as light, falling on a photoreceptor) is changed to a larger signal and response of an entirely different physical nature. When we amplify a radio signal, we amplify the voltage first, then turn it into sound. The latter process may be called transduction. In perception, transduction occurs first, then amplification. Of course, we do have some manmade devices that transduce first, then amplify, though these are often constructed on the basis of living prototypes (photocells, specific electrodes, etc.). The evolution of perception may, then, have begun with the evolution of biological amplification systems (other than mere reproduction).

It is easy to look at ourselves and identify the major systems which are responsible for the transduction component in our perception of the world. These include: the auditory system (hearing), visual system (seeing), olfactory system (smell and taste), and the tactile system (feel and temperature). (Magnetoperception may also occur.). Downstream of these transduction events is the amplification process which is at least initiated in our peripheral and central nervous systems. These advanced systems of perception have evolved to suit our particular life history and position within the ecosystem. We are highly motile animals and thus our systems of perception are positonally wide reaching (hearing and vision, for example). Organisms such as bacteria and unicellular eukaryotes (Protoctista: Margulis, Schwartz & Gould, 1998), which may travel only very short distances in their entire lifetimes, would have little use for such outreach. Thus, we can define a perception field as one of the characteristics of an organism. Humans have a large perception field and bacteria and other unicellular organisms have a small, more local perception field.

One does not normally think of bacteria (Table 1) or Protoctista (Table 2) as having the ability of perception or for even possessing behavior for that matter. However, their rich repertoire listed in these tables suggests that much of our ability to perceive our environment evolved when most organisms were but single cells. For example, using surface receptor molecules single cell organisms are able to distinguish between a wide range of different molecules including amino acids, sugars, oxygen, peptides, steroids, hormones, and energetic molecules (ATP), to name a few. The type of molecule perceived dictates the change in behavior of the organism. That is, if the molecule perceived is a repellent (noxious compounds, for example) then the organism typically moves away, down the concentration gradient of the molecule; and if the perceived molecule is an attractant (food, for example) the organism typically moves towards it, up the concentration gradient. Other molecules perceived may elicit changes in the metabolism of the cell or induce production of molecules that are then perceived by its neighboring organisms.

How does the reception of a particular molecule produce changes in behavior in bacteria and unicellular organisms? In bacteria and unicellular eukaryotes, the basic mechanisms of response to an environmental stimulus are fairly well understood (reviewed in Stock, Ninfa & Stock, 1989) and involve the following steps: receptor > second messenger > response. The transduction mechanism in bacteria may involve a tug on an intracellular "string", i.e., a Marionette model (Stock & Da Re, 1999; Stock & Levit, 2000), as has been suggested in eukaryotes (Maniotis, Chen & Ingber, 1997). In bacteria binding of an external molecule to a surface receptor can cause the receptor to become modified (for example, phosphorylated at specific amino acid residues) which then can result in phosphorylation and activation of transcription factors (called switch proteins) that modify gene regulation (Garrity & Ordal, 1995). In the slime mold Dictyostelium and in yeast, receptor binding can activate G?protein molecules causing an increase in cellular calcium and thus affecting the cytoskeletal motor apparatus (Newell et al., 1988; Whiteway et al., 1989). Binding to receptors in the ciliates Paramecium and Stentor causes a cellular hyperpolarization or depolarization, respectively, that affects ciliary beating (Van Houten, 1979; Wood, 1989).

One might says that the elements described are mechanistically 'cause and effect' and thus may not warrant being called perception. But many of the organisms listed in Table 2 display adaptation in their response to a stimulus. In both vertebrate retinas and in the chemotactic responses of unicellular organisms (Morimoto & Koshland, 1991) adaptation allows the cell sensory system to operate over a wide range, orders of magnitude, of stimulus intensities. In a sense this implies cellular memory.

Experiments demonstrate classical conditional learning in Paramecium (Hennessey, Rucker & McDiarmid, 1979; but cf. Hinkle & Wood, 1994). Paramecia are unaffected by a vibratory stimulus but will rapidly swim away when exposed to an electric shock. If individual Paramecia are conditioned by exposing them to an electric shock paired with a vibratory stimulus they will display rapid swimming movements when later given the vibratory stimulus alone. Thus, at least in Paramecia there exists a higher level of perception. (Classical conditioning seems not to have been reported in prokaryotes.)

Of evolutionary importance, some of these systems found in prokaryotes and unicellular eukaryotes for perceiving their external environment can be found in systems involved in signalling between two vertebrate neurons (Carr et al., 1989). Furthermore, Tetrahymena has been found not only to produce a number of vertebrate?like hormones such as insulin and endorphin but also to possess receptors for these hormones (Csaba, 1996; Leick, Grave & Hellung-Larsen, 1996). Indeed, Haldane (1954) proposed that neurotransmitter and hormonal systems of vertebrates, which perceive the internal world of our bodies, may have evolved from the chemosensory systems that perceive the external world of unicellular prokaryotes and eukaryotes. This idea has been developed by Pertseva (1991).

The bacteria group Archaea, while certainly very advanced and derived now, is believed to represent one of the most primitive forms of life on this earth. As such, we are presently using these organisms as our starting point for our analysis of perceptual mechanisms. For our initial analysis, we chose to determine the presence of two perceptual systems, chemotaxis and photoreceptivity, in Archaea by performing DNA sequence alignments for genes encoding for the Che (chemotaxis) proteins (Abouhamad et al., 1998) and rhodopsin (a visual pigment found in eubacteria and eukaryotes). Using Blast (Altschul et al., 1997), a program which compares DNA and amino acid sequences against those deposited in GenBank, we performed DNA and amino acid sequence alignments using Che and rhodopsin gene sequences from eubacteria against genomic sequences from Archaea. We found deduced amino acid sequences from Archaea which were greater than 80% identical to Che proteins and rhodopsin found in 'higher' organisms (as could have been predicted from the literature we subsequently found: Bibikov et al., 1993; Rudolph & Oesterhelt, 1996; Hoff, Jung & Spudich, 1997; Zhang, Zhu & Spudich, 1999). The presence of these two perceptual systems in Archaea suggests again that perception was well established by the time we have any record of life on the earth. Our analysis in complicated by the fact that horizontal transfer of genes occurs frequently in bacteria, and thus our understanding of the origins of the cell and bacterial phylogeny remain poorly understood (Doolittle, 1999). It is our hope however, that a more detailed analysis of many more components of the different perceptual systems and the completion of more bacterial genome projects combined with functional genomics might provide us with a better understand of the emergence of perception, without having to rely on the hypothetical reconstructions.

We thus hope that it will be possible to construct a phylogeny of perception within the prokaryotes and the single celled eukaryotes, taking into consideration current hypotheses about the symbiotic origin of eukaryotic cells (Lake & Rivera, 1994; Margulis, 1996). From such a phylogeny, we may begin to see how perceptual mechanisms evolved from simple beginnings. We would then attempt to extend these concepts down to the molecular level and up to ourselves. As multicellularity and cellular differentiation are well represented in the prokaryotes (Carr & Whitton, 1982; Shapiro & Dworkin, 1997; Margulis, Schwartz & Gould, 1998), it will prove interesting to see how essential these features, which we ordinarily take as characteristic of "higher" organisms, are to enhanced perceptual abilities.

Acknowledgments: We thank Gerhard Grössing, Lee Doerksen and Natalie K. Björklund for critical readings of the manuscript. Presented in preliminary form in Martin & Gordon (2000).

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Table 1. Bacteria

Table 2. Protoctista

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