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Keynote Address: "Development and Evolution of Eyes and Photoreceptors: From Cyanobacteria to Humans"
Walter Gehring, University of Basel
Recent experiments on the genetic control of eye development have opened up a completely new perspective on eye evolution. The demonstration that targeted expression of one and the same master control gene, that is, Pax6 can induce the formation of ectopic eyes in both insects and vertebrates, necessitates a reconsideration of the dogma of a polyphyletic origin of the various eye types in all the animal phyla. The involvement of Pax6 and Six1 and Six3 genes, which encode highly conserved transcription factors, in the genetic control of eye development in organisms ranging from planarians to humans argues strongly for a monophyletic origin of the eye. Because transcription factors can control the expression of any target gene provided it contains the appropriate gene regulatory elements, the conservation of the genetic control of eye development by Pax6 among all bilaterian animals is not due to functional constraints, but a consequence of its evolutionary history. The prototypic eyes postulated by Darwin to consist of two cells only, a photoreceptor and a pigment cell, were accidentally controlled by Pax6 and the subsequent evolution of the various eye types occurred by building onto this original genetic program. A hypothesis of intercalary evolution is proposed that assumes that the eye morphogenetic pathway is progressively modified by intercalation of genes between the master control genes on the top of the hierarchy and the structural genes like rhodopsin at the bottom. The recruitment of novel genes into the eye morphogenetic pathway can be due to at least two different genetic mechanisms, gene duplication and enhancer fusion.
In tracing back the evolution of eyes beyond bilaterians, we find highly developed eyes in some box-jellyfish as well as in some hydrozoans. In hydrozoans the same orthologous six genes (six1 and six3) are required for eye regeneration as in planarians, and in the box jellyfish Tripedalia a pax B gene, which may be a precursor of Pax6, was found to be expressed in the eyes. In contrast to the adults, which have highly evolved eyes, the Planula larva of Tripedalia has single-celled photoreceptors similar to some unicellular protists.
New results aiming at the decyphering of the eye developmental program in Drosophila by analyzing the transcriptome at larval, pupal and adult stages of development will be presented. Furthermore, I shall present evidence that not only Pax6 is highly conserved in evolution, but also its DNA target sites in enhancers which are regulated by Pax6. As an example the Delta 1-crystallin enhancer of the chicken is interpreted correctly by Drosophila lens - secreting cells indicating that the genetic circuits are conserved even though the lens protein genes are not conserved.
In tracing back the evolution of vision, we have to go back to the earliest history of living organisms.
Sunlight is a primary source of energy for life. Among the oldest known fossils are the stromatolites from Western Australia. They represent cyanobacterial deposits and are some 3500 million (3.5 billion) years old. Stromatolites can still be found in lagoons of Western Australia. They are capable of photosynthesis and light perception by proteorhodopsin, and they show circadian rhythms. Some cyanobacteria have become symbionts of eukaryotic cells, and they have been incorporated first into red algae as primary chloroplasts with two cyanobacterial membranes. Subsequently, the red alga with its symbiont has been taken up by other eukaryotes, where they form secondary chloroplasts with 3 or 4 membranes, two cyanobacterial membranes, a primary host plasma membrane from the red alga, and a secondary host phagosomal membrane. In dinoflagellates (and euglenids) the primary host plasma membrane has been lost, so that they have three membranes around their secondary chloroplasts. Some dinoflagellates have lost their chloroplast and are heterotrophic. Some of these heterotrophs have evolved highly complex photoreceptor structures, ressembling a human eye with “cornea”, “lens”, “retina” and “pigment cup”, all in a single cell. During cell division, these “ocelloids” arise from thylakoid membranes, suggesting that they are derived from the chloroplast. The dinoflagellate, Pyrocystis does indeed contain a proteorhodopsin which is very similar to that of cyanobacteria. Also, in flagellates like Chlamydomonas and Volvox the “eye spot” (ocelloid) is located in the chloroplast, suggesting that the photoreceptors of flagellates and metazoa might originate from cyanobacteria. These considerations lead to the proposal of a “Russian Doll” hypothesis which assumes that photoreception originated in cyanobacteria and was transferred in a least two symbiotic steps to dinoflagellates. It is not known how the most primitive photoreceptors found in cnidarians have evolved: A first hypothesis assumes another symbiotic step from dinoflagellates to jellyfish. Since dinoflagellates are common symbionts in many cnidarians, their “eye morphogenetic genes” might have been incorporated into some jellyfish genomes. Alternatively, colonial flagellates might have evolved their photoreceptors by cellular differentiation.
1. Does long-term memory engage developmental switches in the brain: On seemingly-robust paradigms and shaky memories
Yadin Dudai, The Weizmann Institute of Science, Israel
The textbook account of the neurobiological substrates of memory is that the transformation of short- into long-term memory involves stabilization ("consolidation") that engages experience-dependent modulation of gene expression in the relevant neural circuits. This type of paradigm is anchored in a conceptual framework that depicts memory as a developmental or growth process, and plays a dominant role in the selection and interpretation of molecular data and of models of long-term memory. Recent data call for reassessment of the current dogma. Such data also raise intriguing questions concerning the selective pressure on memory systems to encode the past vs. the future.
2. On the Idea of a Gap between the Living and the Non-living
Evelyn Keller, Massachusetts Institute of Technology
Few scientists today believe that the formation of living beings requires anything beyond physical and chemical processes.
Nevertheless, the notion of a difference between the living and the non-living persists, and despite dramatic successes in unraveling
the physics and chemistry of biological processes, that basic question remains unanswered. Unlike most physical and chemical
systems, living systems must - at the very least -- be endowed with function, a concept that to this day remains indispensable to
biology, yet is effectively missing from the vocabulary of physics and chemistry. Accordingly, we need an account of the evolution of
function out of simple physical and chemical dynamics. This, I suggest, requires abandoning traditional attempts to separate form
from matter, and integrating the dynamics of space, time, and matter with the basic laws of physics and chemistry. As Jean Marie Lehn
puts it, it requires a science of informed matter.
3. From Orientation in Single-Celled Organisms to 21st Century Science: Activity Theory and its Dialectical Materialist Account of Evolution and Historical Development of Human Culture
Wolff-Michael Roth, University of Victoria
In the early part of the 20th century, a form of (social) psychology emerged-largely in the Soviet Union-that is entirely grounded in dialectical materialist method that Karl Marx developed and exemplified for political economy in Das Kapital. Its early proponents and theoreticians were Lev S. Vygotsky, Aleksandr R. Luria, and Alexei N. Leont'ev. The approach subsequently was further developed and extended to cover new disciplinary ground by several generations of psychologists (e.g., Piotr Y. Galperin, Aleksandr V. Zaporozhets), philosophers (Evald Il'enkov, Felix Mikhailov), linguists (Alexei A. Leont'ev), educational psychologists (e.g., Vasiliy V. Davydov, Daniil B. El'konin), and others. Although some Western scholars have adopted the approach at least in its name (e.g., Yrjö Engeström), the dialectical materialist core has disappeared in all but one school: the Berlin group of critical psychology with Klaus Holzkamp as its major proponent, who grounded his work directly in A. N. Leont'ev and further developed it. The dialectical materialist approach is necessary, however, if we want to arrive at a non-dualist, non-reductionist account of culture, cognition, and consciousness that begins with single-celled organisms (the early unit that already contains the possibilities for more developed organisms) and ends up with present-day science. In this paper, I present such an account initiated particularly by A. N. Leont'ev and K. Holzkamp, who attempted to construct a form of psychology that operated with categories consistent with evolution rather than reifications of common sense. The account is based on an approach whereby quantitative changes in the individual organism and the surrounding environment lead to qualitative changes in the evolutionary process, e.g., new dominant structures or functions. In other words, the account is based on a method that explains the emergence of structure (morphogenesis) that ultimately leads through anthropomorphosis and the associated qualitative shift to culture (society) as the carrier of knowledge. I show, drawing on some simple examples, how this verbally articulated transformation of quantitative into qualitative changes is consistent with mathematical models of morphogenesis as these were developed in catastrophe theory (René Thom). I also articulate some reasons that mediated the uptake and realization of activity theory in the form it was conceived. The uptake has been slow because it requires a radical shift in epistemology and ontology and from classical to dialectical logic, from identity to non-self-identity in the way it appears in the theories of language and thought developed by Vygotksy and the Bakhtin circle (Mikhail M. Bakhtin, Valentin N. Volosinov, Pavel N. Medvedev), and in the way it is now realized in the propositions by philosophers of difference (e.g., Giles Deleuze, Jacques Derrida). That is, the same dialectical materialist method accounts for evolutionary and cultural processes such as speciation (qualitative differences) and the cultural development of languages. The purpose of this contribution is to articulate the method and to sketch the account that this method can provide for the historical changes that led from orientation in single-celled organism to 21st century science. For the possible trajectories this development took around anthropogenesis, I will draw on current knowledge about early cultural forms in early and present-day hominids (e.g., apparent tool use among chimpanzees about 4.5ka ago). The approach described here leads to a psychology that does not dichotomize body and mind, material culture and consciousness, the material world and language.
4. Probing the Genetic Basis of Human Brain Evolution
Bruce Lahn, University of Chicago
Human evolution is characterized by a dramatic increase in brain size and complexity. To study its genetic basis, we examined the evolution of genes involved in diverse aspects of brain biology. We found that these genes display accelerated rate of evolution in the human lineage. Some of these genes show evidence of ongoing positive selection within anatomically modern humans. For one of them, evidence suggests that the positively selected allele has arisen through interbreeding with an archaic Homo species such as the Neanderthals.
5. Developing External and Internal Representations
Katherine Nelson, CUNY Graduate Center
Developments in imitation, language, and memory during the first two years of life involve the coordination of internal and external representations. More generally, the human use of external - public - representations, including gestures, mimetic play and drama, language, graphic images and art, writing and printing, and a variety of graphic and solid scientific and engineering abstractions, play vital roles in human cognitive operations. Their use in cognition, communication, and cultural constructions is a unique capacity of humans developing during early to middle childhood, when given appropriate social support. My talk will consider its early development and possible implications for cognitive - and brain - development.
6. The Cambrian Information Revolution and the Fossil Record of Behavior
Roy Plotnick, University of Illinois at Chicago
The Ediacaran to Cambrian transition (ca. 570-530 million years ago) is one of the most intensively studied periods in the history of life, characterized by the profound environmental and biological changes associated with the radiation of metazoans. These include the advent of macroscopic predation, an increase in the size and energy content of organisms, and increased spatial complexity of the seafloor environment. These changes may have driven the origin of macroscopic sense organs, which first appear in the Cambrian, and the evolution of nervous systems and "intelligence." Trace fossils, the preserved record of animal behavior, also undergo a major increase in diversity and complexity during this period.
7. Evolution, Development, and Intelligent Behavior: A Dialectical Interpretation
Alan Smith, University of Utah
Given the fact that intelligent behavior has evolved most dramatically in the vertebrates since the Cambrian period my talk will focus on this group of animals. An outline will be given of the major stages for the evolution of intelligent behavior as well as the important biological mechanisms subserving this behavior. Included will be a discussion of dialectical or genetic logic as a fruitful method for organizing a theoretical framework for understanding some of the main features of this evolution.
8. Making a Self
Marya Schechtman, University of Illinois at Chicago
The “mind-body problem” has been widely discussed. There is, however, a subcomponent of this puzzle –what I will the “self-body problem” – that has received less direct attention. This is unfortunate. Not only is this latter problem important in its own right, it can also help illuminate broader issues of mind and body. My paper will define and investigate the self-body problem, proposing a narrative conception of the self as an answer to it, and describing the more global implications of this analysis for understanding mind and consciousness.
The self-body problem starts from the same intuition that the mind-body problem does, the idea (expressed in some form in virtually every known culture) that we are not simply identical to our human bodies, but are selves or subjects who somehow “inhabit” them. Of course, this understanding of ourselves cannot be taken at face value, but it points undeniably to a phenomenon in need of explanation. The self-body problem is the problem of providing that explanation –saying what a self is and how it is related to its body. This problem differs from the mind-body problem, as I understand it, because the mind-body problem is concerned more generically with how mental phenomena relate to the physical world (or, arise out of it). Selves are not just minds in the most generic sense; they are special kinds of minds. Being a self requires higher-order cognitive capacities like reflective self-consciousness and prudential reasoning. Because of this, it also requires a certain amount of unity over time. As John Locke puts it, a self is a “thinking, intelligent being that can consider itself as itself, the same thinking thing, in different times and places.” To understand selves, then, we need to understand how experiences at different times is unified to become the experience of a single subject. Descartes famously places the unity of self (as have many others) in the simplicity of an immaterial substance. Locke, however, just as famously denies that unity of substance can provide true unity of self. The unity of the self has to be one we experience, and so it must be defined in terms of the relation of mental events understood as mental events and not in terms of the of unity of the entity that produces those events. Locke argues, in other words, that we must understand of our identity o in terms of sameness of consciousness over time, and not sameness of substance. Moreover, these arguments apply just as well to materialist views that define the unity of the self in terms of the unity of the brain as it does to views that define it in terms of the unity of a soul. The difficulty in developing Locke’s insight is to say in more detail what sameness of consciousness amounts to. Standard readings emphasize memory connections and anticipation. These backward- and forward-looking states are taken to be the glue that holds the self together. I argue, however, that as important as these relations are, they are not enough to build a self. Being a self requires that one construct a (largely implicit) life narrative according to which she organizes her experience. It is this narrative that binds together the different temporal parts of a self. Building a narrative of the right sort depends upon learning the cultural conception of the person and applying it to oneself – something that happens only through social interaction and acculturation. Moreover, the complex cognitive capacities that define a self, once developed, depend upon interactions with others. This means that we become and continue as selves only against the background of personal interactions. This is not only a claim about what is required to be able to do what selves do, but also about what is required to have the kind of conscious experience selves have. The sort of self-consciousness and cognitive capacities that make selves require a “space of persons” for their development and maintenance. Our selfhood is thus related to our embodiment not only because it is generated by our organisms, but because it is only through interacting with others as embodied individuals that we are able to live as self-conscious subjects. These facts, once appreciated, point to a new perspective from which broader questions of mind and body can be addressed, one which intersects nicely with recent work on the “extended mind” by philosophers like David Chalmers and Andy Clark.
9. Dialectics of Nature: Integrating Evolution, Genetics and Development 1900-2000
Garland Allen, Washington University
Most of western science -- including the life sciences -- have been dominated since the 17th century by the philosophy of mechanistic materialism and its associated reductionist methodologies. While mechanistic thinking has produced some remarkable results, it has also had its limitations, nowhere more apparent than in the biological sciences. Although traditional physical systems have proved to be more complex than was thought in the mid-19th century, biological systems have always presented investigators with complexities that at times seemed insurmountable. Historically, this has led to a constant juxtaposition, or dialectic, between mechanistic and holistic approaches, most clearly demonstrated by the "mechanist-vitalist" debates of the nineteenth and early twentieth centuries. While it has been fashionable (historically and philosophically) to dismiss vitalist claims as hopelessly metaphysical, there was often an important philosophical position embedded within vitalist and other holistic arguments. I will argue that by adopting a consciously dialectical materialist account of biological (and all scientific) phenomena, it is possible to not only avoid the fruitless debates of the past but to provide insights for asking new sorts of questions and provide new directions for research. While this claim is applicable to all the life sciences, I will argue that it is particularly applicable to embryology and its attempted integration with evolutionary theory.
10. An Experimental Frame Work for Molecular and Cellular Cognition: Implications for the Evolution of Cognition.
Alcino Silva, UCLA
Since genes are at the heart of evolution, experimental results concerning the evolution of cognition must include genetic mechanisms and their actions on cellular, neurosystems, cognitive and even social phenomena. One of the fundamental conceptual problems with the idea that genetic changes could have shaped our complex multifaceted cognition is rooted in deep-seated beliefs about emergent properties at every level of biological complexity. The canonical idea is that at each level of analysis there are properties that cannot be ascribed to any one component, but that simply emerge from the collective output of interactions amongst these components. These emergent properties affect the collective behavior of components in the next level of biological complexity, which in turn have emergent properties of their own and so on. An implicit assumption of this framework is that explanations of cognition must follow this itinerary of levels, with mechanisms at one level accounting for those in the next, and emergent properties interfering with direct connections between lower and higher levels of biological complexity (e.g. thus, preventing direct causal connections between molecular and memory phenomena). Even though the concept of emergent properties is useful, I propose that the assumption that it restricts the range of causal connections is not: First, since genetic changes clearly drive evolution, it follows that there are meaningful mechanistic connections between genes and cognitive function. Second, there are now thousands of convergent lines of evidence from the new field of molecular and cellular cognition that unequivocally demonstrate that molecular and cellular mechanisms can be compellingly and meaningfully connected to nearly all cognitive functions, from memory, to attention, emotion, etc. I will present a new framework for experimental neuroscience that addresses the problems raised above, and provides an intellectual structure for experimental approaches in the new field of molecular and cellular cognition. Briefly, this framework is built on two main hypotheses, which I will refer to as the Experimental Triptych (or E3) and the Convergent Four. E3 proposes that there are three main activities in experimental science: (1) discovering new phenomena (e.g., a kinase, a cellular physiology, a circuit architecture, a behavioral property, etc.), (2) making connections among phenomena (e.g. connecting a kinase with a synaptic physiology such that the actions of the kinase become interwoven into the synaptic physiology in question, etc.), and (3) developing tools/methods for doing (1) and (2) (a new optical physiology method, a new behavioral paradigm, etc.). The Convergent Four (C4) is focused on the second component of E3. C4 proposes that there are four fundamentally different strategies that scientists can use to test a connection between two phenomena of interest (e.g., A and B), and that to causally connect A to B it is crucial to develop independently confirmed lines of convergent evidence in each of these four categories. The four categories include negative alteration (decrease probability of A or p(A) and determine p(B)), positive alteration (increase p(A) and determine p(B), non-intervention (examine whether A precedes B) and integration (develop ideas about how to get from A to B and integrate those ideas with other available information about A and B). In this new framework there are no a priori limitations on what A and B can be, and only experimental methods/techniques limit the possible connections between any two natural phenomena. I will discuss this view and its implications for understanding the evolution of intelligence.
TBA
Terrence Deacon
John Allman, California Institute of Technology
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