“ASSESSING A MULTILEVEL CAUSALITY MODEL
IN THE EVOLUTION OF COGNITION”
MSc in Brain and Cognitive Sciences
Behavioral Neuroscience track
By: Vanessa Del Pozo Sánchez
Student no: 11104066
First assessor:
mw. dr. Federica Russo
Second assessor:
dhr. dr. Hein van den Berg
Date: 28/June/2017
Abstract
Cognition is the mechanism by which an organism is able to acquire, process, and retain information through senses and experiences. To this day, there is no agreement regarding its evolutionary explanation. The literature describes a wide range of methods in order to understand components such as motor behavior, thought, consciousness, memory, perception, and language, among others. This is done with the aim of complementing the origin of the evolutionary processes of cognition. However, none of these approaches has considered the evolution of cognition as a result of a network of complex interactions at different levels of organization. In this thesis, we introduce a multilevel causality model for the understanding of the adaptationist idea of cognition. The model is built by integrating three evolutionary processes: ontogeny, phylogeny, and Evo-devo. The model allowed us to fill the failures that evolutionary processes presented. Thus, we can conclude that with more detailed studies of multilevel causality in the biological systems of cognition, we can develop complete explanations of evolutionary mechanisms that occur at certain level, and observe their consequences at other levels.
Index
General introduction 3
1. Historicity of cognition and Dennett’s adaptationist approach of cognition 4
1.1 History of cognition from Lamarck onwards 5
1.2 Cognition: an adaptationist property according to Daniel Dennett 10
1.3.1 Evolution of simple entities by Dennett 11
1.3.2 From simple replicators to the nervous system 11
1.3.3 Phenotypic variation and the understanding of cognition 13
2. Ontogeny and the “theory of neuronal group selection” in the understanding of cognition. 15
2.1 Introduction 15
2.2 Edelman and the variation and selection within neural populations 15
2.2.1 The three main tenets of the theory of neuronal group selection. 16
2.2.2 Degeneracy and value 18
2.3 Edelman’s theory applied to the immune system 19
3. Evo-Devo: an extension to cognition 20
3.1 Introduction 20
3.2 Evolutionary developmental biology theory 21
3.2.1 The neural system from an Evo-Devo perspective. 22
3.2.1.1 Types of constraints 23
3.3 Evo-devo and cognition 24
4. Multilevel causality models and cognition 26
4.1 Introduction 26
4.2 The understanding of adaptation 26
4.3 Difficulties in the explanation of cognition by the adaptationist approach. 27
4.3.1 Difficulties in Dennett’s approach and ontogeny 27
4.3.2 Analysis of Edelman and Dennett’s theories: differences and similarities. 30
4.4 Multilevel causality 31
4,4,1 Types of multilevel causality 31
4.4.1.1 Bottom-up causality for the understanding cognition. 32
4.4.1.2 Top-Down causality and cognition 34
4.5 Integration of types of multilevel causality model to understand cognition 36
Conclusions 38
References 40
Introduction
Evolution refers to the process by which species respond and adapt to the environment as a result of maximizing their fitness. Changes occur at all levels -from protein synthesis to behavior- in order to predict and even manipulate environmental regularities. One category of such mechanisms of response and adaptation is cognition: the process by which an organism is capable to acquire, process, and retain information through senses and experiences. Therefore, cognitive capacities in animals -including the human being- can be studied as phenotypic traits within evolutionary biology.
The general objective of this work is both to show how cognition develops and to address those of its elements that allow an adaptive explanation. We focus on evolutionary processes through ontogeny, phylogeny, and evolutionary developmental biology, all of which deal with the development of cognition in animals with a central nervous system. Then, by combining the study of these evolutionary processes, we can apply the multilevel causality model as a tool to understand the evolution of cognition in the adaptational approach.
This work will be structured in the following manner:
- To identify the epistemically significant features of cognition, it is necessary to know the philosophical and historical approaches by which it has been studied. In the Chapter 1, we present how the understanding of cognition has developed trough time, and then we include an analysis of the main ideas of one of the ultra-Darwinian authors in adaptation of cognition: Daniel Dennett.
- In Chapter 2, we describe an evolutionary take on cognition from the ontogenetic perspective. We analyze the theoretical arguments of neural Darwinism given by the neurobiologist Gerald Edelman, the essence of whose argument is based on an analogy of evolution by Darwinian natural selection at the cellular level. Edelman argues that a selection process is carried out at the level of neural groups in the nervous system of some mammals. With this, he explains the emergence of such cognitive phenomena as perception, memory, and consciousness.
- In Chapter 3, we review the explanations from developmental evolutionary biology (Evo-Devo) regarding the origin of the variations for which natural selection applies. In order to understand the weight those variations have in an adaptive explanation of cognition, we also examine the role of natural selection itself in the arguments of the Evo-Devo.
- In Chapter 4, we develop a multilevel causality model. To do this, it is essential to understand what a multilevel causality model is and how does it work. After that, we construct a model of cognition that integrates ontogeny, phylogeny, and evolutionary developmental biology. Our motivation stems from the idea that biological systems are organized hierarchically in levels, which range from molecules to ecosystems. Lower levels limit the higher ones, but these in turn also influence the first in a reciprocal causal dependence. Finally, in the last section, we present the conclusions of our work.
1. Historicity of cognition and Dennett’s adaptationist
approach of cognition
1.1
History of cognition from Lamarck onwards
Even though there have been many attempts to categorize living beings, from Aristotle to Cuvier, it was not until the early nineteenth century that the French naturalist Jean B. Lamarck –in his work Philosophie Zoologique (1809)– created a classification of the animal kingdom based on the degree of intelligence that each animal presents. As such, Lamarck can be seen as the first one to study cognition with an evolutionary approach (Atran 1993). The classification proposed by Lamarck was based on functional correlations of brain structure, and it rendered three large groups: apathetic, sensitive, and intelligent. Within the apathetic group, we could find cnidarians, sponges, and worms. Crustacean mollusks, insects, arachnids, echinoderms, and myriapods were part of the sensitive group. Finally, the intelligent class was made up of all vertebrates.
Based on his classification, Lamarck divided the animals into evolutive stages. He devised a new system –the system of “perfection”–, where the simplest existing animals rose progressively to the most complex or “perfect” animals. Just as in the “Scala naturae” of Aristotle, the highest level in this stepwise process was occupied by humans. Only at the highest level did the organisms display psychological functions such as memory, judgment, attention, and thinking (Papini 2009).
In the 1870’s, Charles Darwin, another revolutionary figure of the natural world, published two books that referred to the evolution of the mind. His work “The Descent of Man and Selection in Relation to Sex” (1871) established that mental characteristics –including moral and social instincts in humans– are inherited in the same manner as physical characteristics, namely by variation and Natural Selection (NS). In the other book, entitled “The Expression of Emotion in Man and Animal” (1872), Darwin brought into discussion the concept of emotion. He claimed that emotions are just like any other characteristic, so that they too undergo adaptations and evolve. He compared facial expressions of some primates against humans’ facial expressions, finding out that facial expressions were sometimes caused by desires and sensations unleashed by the nervous system.
Lamarck and Darwin were revolutionary naturalists that both gave way to a new paradigm that featured ideas we now associate with cognition. In fact, Alfred Giard, an important zoologist who published his findings during the 1880’s, considered that Lamarckism and Darwinism were actually complementary theories, and he supported this idea with studies on evolutive convergence. For example, he put forward a classification of organisms based on their behavior in their natural environment, and did this with a Lamarckian approach (Peláez del Hierro et al., 2002).
Carrying on with our chronological review, we must mention Douglas Spalding, who is regarded as one of the founders of ethology and who published his first work, entitled “On instinct”, in 1872. His overall studies brought him to the conclusion that instincts are a guide for learning and for inherited capacities (Thorpe, 1979;; Gray, 1967). Similarly, George Romanes, an evolutionary biologist and psychologist who set the foundations of comparative psychology, proposed general principles for the evolution of the mind based on psychological capacities rather than physical relationships between animals. He presented them in his book “Animal Intelligence” (1882).
Karl Lashley, a behaviorist from Virginia, carried out studies on intelligence, behavior, and the neuronal basis of certain cognitive processes as of the 1920’s. He focused on brain physiology and psychology, trying both to find the locus of specific memory traces and to describe the behavior of the mind with mathematical and physical concepts. His contributions to the study of cognition were based on the different types of tests that he ran throughout his life. He sought to understand the inconsistencies between different types of learning tests for a variety of different animals, which spanned from rats to monkeys (Lashley, 1929;; Lashley, 1950;; Lashley 1951).
In the middle of the 20th century, authors such as Niko Tinbergen and Konrad Lorenz, Nobel Prize winners for their work in organization and elicitation of individual and social behavior, rewrote the concepts of ethology. Tinbergen introduced four basic questions in order to characterize an evolutionary approach of behavior (Bateson and Laland, 2013): I) What is the objective of a given behavior? II) How did it develop during the lifetime of the individual? III) How did it evolve over the history of the species? and IV) How does it work? Lorenz, in turn, studied behavioral phylogenies –for which Natural Selection also takes place–, as being guidelines for animals’ instincts (Papini, 2009). Both authors worked under the scope of Darwinism, and they brought it about that evolution of behavior was treated as part of the process of NS. Following this approach, William Hamilton, a theoretical evolutionary biologist considered as one of the biggest influences of the 20th century, conceived a mathematical
model of genetics that incorporated both the “coefficient of relationship” –a concept defined by Wright– and the maximizing property of “Darwinian fitness”. The combination of these theories allowed him to model the link between the fitness of species and the evolution of behavior, based on the interactions among such species (Hamilton, 1964). Shortly after, and as a follow-up of his previous work, Hamilton published an article that used neo-Darwinian principles to explain the behavior of a society as based on paternal care (Hamilton, 1964).
In 1975, Edward Wilson, an evolutionary and socio-biologist, defined the systematic study of social behavior by the integration of three different factors: population’s genetics, evolutive ecology, and demography. With this, Wilson tried to extend the focus to other forces that could be guiding behavior as well, and did so with a neo-Darwinian approach.
In 1971, Daniel Dennett, one of the most outstanding philosophers of science due to his work in the cognitive sciences, proposed that animals have beliefs. He considered beliefs as “cognitive states that suffice to account for the perceptualocomotory prowess of animals” (Dennett, 1971). With such ideas, one would be able to predict behavior by adopting an intentional stance1.
In his book “The Architecture of Cognition” (1983), the natural philosopher John Anderson tried to explain what is referred to as the modular approach to cognition. He considered that cognition is a process built by quasi-independent modules that become associated with each other in order to construct a higher function. In this multi-module and multi-level process, the degree of complexity for said construction is determined by the size of the brain, a hypothesis commonly known as “encephalization hypothesis”. His theory established that there is an allometric relationship between body mass and brain in all mammals. The hypothesis also states that mammals with brain size bigger than “normal”, where the term “normal” depends on their body mass ratio, also have enhanced cognitive abilities (Boddy et al., 2012).
Patricia Churchland, a philosopher contemporary of Anderson who has contributed to the fields of neurophilosophy and philosophy of mind, studied the relation between mind and brain, focusing on the role of neuroscience in cognitive science within a philosophical context (Churchland, 1984;; Churchland, 1989). She argued that in order to have an understanding
1According to Dennett, there are three different strategies that we might use when confronted with objects or systems: the
physical, the designs and the intentional stance. We use each of these strategies to predict and thereby to explain the behavior of the entity in question. Particularly, when he refers to an intentional state, he refers to the mental states such as beliefs and desires which have the property of “aboutness,”that is, they are about or directed at, objects or states of affair in the world (Jones, 2013).
of the mind, we first needed to understand the brain. For her, consciousness does not exist;; it is just an epiphenomenon of a cerebral function and should be considered only as term that humans have developed with aims of understanding such a function. According to her, such a term will eventually disappear from science.
None of the authors mentioned above studied cognition from a truly biological standpoint. For example, Daniel Dennett used to refer to “cognition” as the process of manipulation of information. As opposed to these takes, then, Fiddick and Barrett (2001) aimed to give a suitable explanation of cognition as ensuing from the concept of Natural Selection. They considered that adaptive cognition should be studied by taking into account a) natural history, b) evolutionary changes, and c) an ecological, functionalist perspective. Thus, they advocated for an interdisciplinary study that included different methods, laboratory studies, phylogenetic and comparative approaches, developmental studies, and neurophysiological dissociations.
Supporting Fiddick’s and Barret’s ideas, Daniel Dennett himself suggested to study cognition from a different angle, since up until the 20th such a study had been confined to an ideology and methodology based on old-fashioned experimental psychology. In turn, he proposed that in order to complement the biological studies of cognition, science should also tackle both the concept of “the mind” and the mental states commonly known as desires and beliefs. With this wide-reaching approach, it would be possible to develop models, theories, and explanations that could prove useful in the understanding of rational agents. This new approach is nowadays known as “cognitivism”. Cognitive authors do not believe in the existence of a soul or ego that rules someone’s behavior. They rather interpret the mind and mental states as ensuing purely from the physical qualities of the brain, and have concluded that there should be no distinction between mind and brain.
For authors like Merlin Donald, a Canadian psychologist, cognitive neuroscientist, and neuroanthropologist, cognition is “the mediator between brain and culture”. In this case, human cognition is seen as having emerged from the primate mind during the earlier stages of human evolution. As for the rest of species, he considers that they can show some relatable characteristics as reflexes, instinct, curiosity, behavior, and memory, among others. However, his thesis does not support the idea that there is any continuity of these aspects from the less complex organisms to the most complex ones.
From a genetic approach, Richard Lewontin, an evolutionary biologist and geneticist who opposes genetic determinism, explains how although genetic mechanisms are usually
considered in the study of behavior, the precise paths of such genetic mechanisms for cognition are still unsolved. One assumption of his work is that, instead of the analysis of the biochemistry of genetic mechanisms in cognition, we could study these changes through Natural Selection. He also argues that the evolutionary questions of cognition are not related just to the evolution of cognition itself, but also to the effects of cognition on evolution (Lewontin, 1998). Thus, he became a pioneer in this track of the study of cognition.
Moving forward, we mention the philosopher and linguist Karen Neander, who introduced a different definition of cognitive systems: “systems adapted for producing and processing internal states that carry information, and for using these states to adapt the bodies in which they are situated to the environments in which they, in turn, are situated and vice versa”. From her perspective, there is indeed a distinction between mind and brain, and moreover, the environment will also play an independent role (Neander 2007).
For Neander and Dennett, cognition is a characteristic that can be found in all organisms. For example, they support the notion that organisms such as plants or fungus can in fact receive information from the environment, process it, and respond to it. This issue had previously been questioned by philosopher of biology Peter Godfrey-Smith, who coined the term “proto- cognition” in order to refer to the cognition of plants and bacteria;; “capacities for controlling individual growth, development, metabolism, and behavior by means of adaptive response to environmental information” (Godfery-Smith, 2002). However, two objections can be made: firstly, this description of proto-cognition does not take into consideration evolutionary changes, and secondly, the definition implies that the proto-cognitive characters may well be seen just as an extended part of behavior or development.
Based on the controversy that the differentiation between “proto-cognition” and cognition was causing, the American philosopher Hilary Kornblith tried to come up with a solution in 2007, arguing that the term “cognitive organism” should be used for those organisms that not only receive and process information, but that can also make a representation of such information.
Dieguez tried to find a different solution to this problem and thus divided the organisms into two different categories: on one hand, organisms with internal representations, and on the other, organisms with mental representations. The first group of organisms is comprised by those that, after a stimulus, are capable of responding, and such a response may or may not cause a deterministic change of behavior. Internal representation is something that all known types of organisms present during their life. For the second kind of organisms –the
organisms with mental representations– the representations have a neural basis, and can be evoked without a stimulus: both the production of a new memory and the remembrance of an old one can activate neural activity. Thus, this kind of representation is found only in animals with a complex nervous system (Diéguez, 2011).
Horik and Emery, a duo of psychologists, analyzed the possibility of a link between cognition and specific aspects of species’ lives. In this case, cognition is not related only to the organism itself, but to sociality, culture, tool use, and behavioral flexibility, among others. As such, cognition influences more than just one environmental selection pressure at a given time. It is important to mention that Horik and Emery side with the view that all organisms possess cognitive characters. For them, it is likely that different species who shared analogous environmental selection pressures evolved with similar cognitive abilities. This explained the wide variety of cognitive characteristics and, at the same time, implied that all animals share many fundamental cognitive abilities, but with a different development of them (Horik & Emery, 2011).
Recently, Dennett offered a description of the origin and evolution of cognition with a phylogenetic and functionalist angle. From his perspective, NS is the main protagonist of the story. His explanation goes from the origin of cognition in the first replicating organisms, to the origin and evolution of the nervous system and its function. He stresses the importance of brain plasticity for cognitive abilities such as learning. In this way, Dennett's arguments lend themselves adequately to the treatment of how a phylogenetic and adaptive account of cognition is constructed. Due to this, in the following section we focus on Dennett’s theory.
1.2
Cognition: an adaptationist property according to Daniel Dennett
In 1993, Daniel Dennett described an adaptationist approach of cognition in his work titled “Consciousness Explained”. His work, opened a new tendency in the comprehension of cognition under the Ultra-Darwinism scope, explaining that cognitive properties, as consciousness, are also subjected to natural selection processes. In order to support his work, he proposes a phylogenetic hypothesis of the phenomenon by which cognition could give rise, describing a series of events that could occur through populations of different organisms. In the next section we will explain in detail his hypothesis.
1.3.1 Evolution of simple entities by Dennett
For Dennett, the extremely rudimentary lifeforms are called “replicators”, and probably the earliest ones in the history of life on this planet, were even simpler than actual viruses (Zawisizki, 2014). Then, for the simplest replicators, the only way to continue replicating, the replicators had to take the good things, repel the bad ones, and ignore the neutral ones that the environment offered. (Dennet, 1993).
The variability of the replicators was given by faults during replication. The copies of faults propagated, and the ones that survived were the ones that presented a higher fitness2. In
these terms, we will be talking about NS and mutation, given by a genotypic variation. Thus, the evolution by NS will lead to particular types of changes in the population of replicators, given by the maintenance of the characteristics that increase fitness.
According to Soberón, an ecologist interested in evolutive biology, in the study of evolution there are a series of properties that an entity has to have in order to be considered as an “Evolution Unit” (EU): i) the replicator has to have a phenotypic variability, ii) at least a part of that phenotypic variability has to be heritable, iii) the heritable variability could be related with the probabilities of the survival and replication of the replicator. Soberon claims that if an entity meets the first two requirements, then it can be considered as an EU, and if all three conditions are met, then the entity can be considered as a Darwinian Evolution Unity (DEU). Given this, according to Dennett's description of replicators, the simpler replicators were DEU and EU.
1.3.2 From simple replicators to the nervous system
The nervous system is a complex and specialized system. In order to generate such system, it is necessary the association of specialized cells. These cells, have evolved to respond and discern to external stimulus. In 1993, Dennett suggested that “protoneurons” evolve through NS, developing an unstable membrane potential, that propagated into other population of cells. After, the diversification of neurons was given by morphological changes as the increase in the size of dendrites and axons, giving rise to a more complex network. In that sense, this also gave place to the specialization of neurons, in which, some of them will focus on the processing of information, or work as motoneurons, among other things (Angrino, 2010).
2 “In the crudest terms, fitness involves the ability of organisms— or, more rarely, populations or species— to survive and
The evolution of simple entities into networks gave place to three different types of nervous systems that we find in the present phyla. According to van-Wielink, a neurologist specialized in neurodegenerative diseases, the first type of neural system is constituted by an nonsynaptic net of cells that is present in less complex animals, as cnidarians and echinoderms, characterized by single units that communicate each other by calcium waves and other impulses, to control simple actions. In contrast with this, there are some authors that postulate that this can not be considered as a nervous system, instead, this will represent the most primitive system, being considered as the precursor of the nervous system due to its lack of synaptic junctions and less specialized cells in contrast with neurons (Jacobs et al., 2007).
The second category is characterized by the presence of ganglion. This system is found in animals that represent the next stage in evolution, in terms of complexity, as arthropods and annelids. In this system, the neurons are no longer single units, in contrast, they build a segmental ganglion, that as the name says, will modulate a segment of the body, and will be connected to the next ganglion by “connectives”.
Finally, the last category is the most complex and its found in chordates. It is characterized by the presence of a neural tube and the cephalization of the system. It is divided into central nervous system and the peripheral nervous system. The communication between cells can be by electrical synapses and chemical synapses, and/or extrasynaptic release. This nervous system gives rise to more complex systems in terms of intelligence.
Dennett (1993) makes evident that for primitive animals with a simple nervous system, the signals from the environment were innately modulated. As for what he called “proximal anticipation” behavior, to respond into an immediate future, and “short-range anticipation” behavior, to the capacity of an animal to produce a more elaborate response than a reflex. He states that these behaviors are really flexible, and so, be consider as highly adaptive characters, that contributes to the fitness of an organism that can be extended into populations.
Despite Dennett's functionalist approach, to explain the primordial behavior of the first animals with a nervous system, he only tells us that they are equipped to solve ecological problems. The cognitive tools that appeared since very early times and that we all possess now, like the reflexes, the orientation and the capacity to recognize objects, are only one face of the currency of what can really be deduced from the origin of evolution of cognition.
Without being able to explain the ecological contexts of selective pressures, whether a niche is chosen or created, whether they were only instinctive characteristics or manifested as emotions, among other things.
1.3.3 Phenotypic variation and the understanding of cognition
Following Darwin's theory, the design that animals own is not always the most fitted for a specific environment. However, the ones that are able to redesign will be the ones that will survive and reproduce. This means that there is a certain level of variation to which we can resort to our life depending on the eventualities that arise. This characteristic is called “phenotypic plasticity” (Dennett, 1993).
Thus, in terms of cognition, natural selection has been responsible for designing cognition, acting on the variations of nervous systems that have existed, leaving only those who responded effectively to environmental interactions and who could inherit the characteristics that helped to survive their carriers.
Dennett claims that when the “plastic brain” is exposed into novel things in its environment, the brain reorganize. The process by which this happens is by a similar process than natural selection. Everything starts in an individual brain by postnatal fixation. In this case, the brain structures that are select, will be the ones that can control or influence behavior. The mechanic process of elimination will lead selection, that at the same time, it has a genetic background. In this case, the organisms with brain plasticity will have an advantage over the ones that does not, and this might accelerate evolution by NS.
For Dennett, the “good tricks” that an animal learns during its whole life are going to improve the animal fitness. This claim, gives a lot of things for granted, and specifically, not all the good learned tricks will lead to a higher probability of reproduction, and therefore the fixation of the character, will not occur. For example, a chimpanzee can learn how to use a tool to take the termites from their holes. However, this does not assure him that he will become the alpha male of the herd and then have more chances to reproduce. In response to this issue, Diéguez (2011) proposes that natural selection acts on individuals with a tendency to have certain cognitive abilities. The selection would have been produced by the disposition to learn them. Thus, learning the “good tricks” would have easily passed the next generation in a non-genetic way, however, what is genetically passed is the disposition to learn them.
In summary, Dennett's evolutionary explanation tells us that cognition is a product of natural selection, acting on the variations in the different nervous systems that are responsible for producing cognitive phenomena. Animals that have cerebral plasticity, are those that have been able to evolve to a "more complete" cognition. The complexity of cognition leads to those that apart from the recording and processing of information, also have a representational system of the information that comes from the environment, that is, they may be able to have beliefs and desires about the environment. Finally, with cerebral plasticity, new neural connections can be formed, triggered by the experiences that individuals have throughout their lives, thus contributing to their survival and reproduction.
As we could see, cognition is diverse, but is not impossible to find a common type of evolutionary story that could apply to most of the cases. Nowadays, cognitive and behavioral neurosciences aim to study the brain and its functions using a wide range of methods. Within the most popular techniques to record the brain activity we can find: electroencephalography, magnetic resonance, electrophysiology, among others. These techniques are use in order to understand mechanisms such as motor behavior, thought, consciousness, memory, perception, language, among others. At the same time, other sciences as the philosophy of mind, the ecology of behavior, cognitive paleoanthropology, artificial intelligence, and evolutionary psychology are using their own scientific methods to complement the origin of the evolution processes of cognition. To postulate a multilevel causality for the understanding on the adaptationist idea of cognition, first we need to introduce the processes that we would like to use. So, in the next chapter I will present the first process, ontogeny.
2 Ontogeny and the “theory of neuronal group
selection” in the understanding of cognition.
2.1
Introduction
Ontogeny is the origination and historicity of an organism, from egg fertilization till its death. Along with its life, the organism will undergo physical and behavioral changes that can be due to external factors (environmental interaction), or internal factors (epigenetics). In 1977, Stephen J. Gould, one of the most influential evolutional biologist from the XX century, stated that evolution will occur when ontogeny is transformed. This transformation can be due to an introduction of new characters or by the change of an old character. Following this, the change of an old character will have a regulatory effect, that will change the rate for features already present, and the introduction of a new character might give rise to a new feature.
The understanding of how cognitive capacities are build giving the present brain structures, it is essential in the study of cognition. In 1987, Gerald Edelman, a biologist winner of a Nobel Prize due to his work on the immune system, proposed a theory to apply Darwin’s theory to the evolution of cognition, in which, he claims that all cognitive functions have a biological support that lay in the brain. Indeed, those properties will be regulated by NS and will apply to all organizational levels from biochemistry to morphology. In this theory, he applies NS on a different level than Dennett. In this case, Edelman speaks about a population of cells instead of populations of individuals. In this chapter, I will like to explain and try to relate Edelman’s evolutionary explanations about the cognitive properties that might complement the understanding of cognition under an adaptationist scope.
2.2. Edelman and the variation and selection within neural populations
The theory proposed by Edelman called “Neural Darwinism” or “The theory of neuronal group selection” (TNGS), tries to fill the gap between biological bases and cognitive psychology. All started with the necessity of merging two different observations of brain function.
One of the observations was the structural and functional variability of an individual nervous system. According to Edelman (1987), the variability will be present at a molecular, cellular, anatomical, physiological and behavioral level in time and space. To explain this variation
between individuals, even from the same species, Edelman claims that the adaptive characteristic will emerge in the course of an individual development (ontogeny).
The second observation relies on the understanding of the development of such adaptive characteristic and its relation with the world stimuli, i.e., “in order to survive in its econiche3, an organism must either inherit or create criteria that enable it to partition the world into perceptual categories according to its adaptive needs” (Edelman, 1993).
Furthermore, Edelman argues that the ability to categorize a novel input from the environment and respond to it, from an adaptive perspective, comes from processes of selection upon variation, instead of the presences of a semi fixed neuroanatomy that just reads the manual of instructions in order to respond and adapt (Edelman, 1993).
In this case, if no individual result of sexual reproduction is identical, then, no two brains are alike. Each brain has its own developmental process and is constantly changing during its life spam. Edelman and Tononi (2000) point out that during the process of natural selection the phenomenon of correlative variation can occur where a “primary trait can be selected for and bring along another changes that are used later for other selective events” (Edelman and Tononi, 2013). For example, selection of an enlarged brain structure to facilitate perception may be accompanied by the enlargement of other neighboring regions in the brain and subsequently these regions may be selected to perform another function, such as memory.
2.2.1 The three main tenets of the theory of neuronal group selection.
The Neural Darwinism theory is built under tree main tenets explained below:
1. Developmental selection. Darwinian natural selection and evolution is usually
studied in populations of organisms, but when it applies to cellular populations;;
is called “somatic” evolution. Such somatic evolution tends to reduce
cooperation among cells, thus threatening the integrity of the organism
(Edelman 1994). Given the above argument, genes and inheritance give the
formation of an initial anatomy of the brain. However, the connectivity of
synapses is established by the somatic selection during each organism
development.
3 The econiche definition stills controversial, however, in this work we refer to econiche to “what describes a
species’ ecology, which may mean its habitat, its role in the ecosystem, etc” (Pocheville, 2015).
As an example, during neurogenesis, dendrites and neurites will mature,
giving rise to new branches that grow in several directions. This will give rise
to new patterns of connection, which in turn will produce a vast and varied
repertoire of neural circuits. Then, according to neural individual patterns of
electrical activity, neurons will create populations, ending in a system in which
“neurons that fire together, wire together”. As a result, neurons of a population
will be more closely associated to each other that to neurons in other
population. (
Edelman and Tononi, 2013).
2. Experiential selection. The process of synaptic selection will occur inside the
repertories of already existing groups of neurons due to behavioral
experience. For example, the maps of the brain that corresponds to a finger
response can change their confines, depending on the use of them. When a
finger is trained to be used in a certain way, then, the synapses between
populations on charge of this response will get strength, without any
anatomical changes (
Edelman and Tononi, 2013).
3.
Reentry. This tenet allows the integration of the previous two
tenets
, leading to
the
synchronization of the activity of groups of neurons in different brain maps,
transforming them, temporarily, into a big circuit with a coherent output.
The
ability that we have to discern between movement and shape in a display of
moving dots, due to the integration of different brain areas, is an example of
this (
Edelman and Tononi, 2013).
The reentry of connections between
neuronal groups in diverse parts of the brain by a single stimuli sense by
different senses, will coordinate the impressions from all the senses to provide
a coherent, consistent, continuous experience. The reentry of information also
will provide a mechanism of re-categorization
4, the fundamental process by
which the brain carves up the world into different things and recognizes those
it has encountered before.
4
The word re-categorization, it is not to be taken as implying the existence of a prior set of categories: in fact, every act of recognition modifies the category.
In this theory, Edelman stress out the importance to high-order processes -as thinking, planning, perceiving, and language-, in which concepts are maps of maps of the brain, which will get rise from the re-categorization of the brain activity. The first –order of consciousness will be given by the concepts by themselves, and in human consciousness, we will also find the features of a secondary consciousness as the concepts about concepts, language, and a concept of the self, that will be built on the foundation of first-order concepts.
In summary, in terms of cognition, some patterns or population connectivity’s will be reinforced by experiences, while many others will be eliminated in a selective process. Some other type of research supports this theory, as the consolidation and reconsolidation of memory (Edelman y Tononi 2000;; Nader et al., 2000). Neural Darwinism attempts to explain how some cognitive abilities emerge at the cellular level. Neural Darwinism is an incomplete analogy to the historical process of Darwinian natural selection. The difference is the time scale and the selection units. In this theory, the entities under natural selection are the neural groups. The first stage of selection occurs during the embryonic development of the individual. This first pattern of connections between neural groups are those given by value systems. The second stage is the selection given by experience, which occurs during the postnatal stage and until the death of the individual. Contact with the environment creates modifications between the different connections of the neural groups with degenerative characteristics and as a consequence gives a flexible or plastic property to the neural groups. Finally, the process of re-entry is all the reciprocal connections that are distributed throughout the brain, which marks the coherence to produce the cognitive phenomena.
This whole repertoire known as neural Darwinism is the basis for understanding how cognition develops in each individual. There are other elements that complement this theory and which I consider below.
2.2.2 Degeneracy and value
The theory argues the existence of another essential and unique property that all the selective systems will share, denominated “degeneracy”. This property refers to the ability of structurally different variations of brain elements to produce the same function, i.e., “many different ways, not necessarily structurally identical, by which a particular output occurs” (Edelman and Tononi, 2013). For Edelman and Tononi, this property will occur at one organizational level or across a multiple, otherwise, all mutations would be lethal.
Finally, another key idea in the theory is value, a word used here to describe inbuilt tendencies towards particular behavior. These forms of behavior may be driven by what we
value in a fairly straightforward sense - seeking food, for example, but they also include such inherent actions as the hand's natural tendency to grasp.
2.3 Edelman’s theory applied to the immune system
Edelman constructs an analogy of TNGS with what happens to the immune system. In this case, instead of population of neurons, the entities under NS are the antibodies. He proposes that from a vast variety of antibodies, the ones that will be selected to rapidly reproduce will be the ones that linked successfully to the target molecule. That at the same time, increase the fitness of the organism. In this case, the immune theory, from which Edelman formulates his analogy, postulates that there is no possible way that the body will have all the antibodies for all the foreign substances that could attack an organism. In contrast, the body will rapidly produce an antibody for substances it has never encountered before (and indeed for substances which never existed in the previous history of the planet). In an analogous way the TNGS explains how the brain can recognize objects in the world without having a huge inherited catalogue of patterns.
On the contrary, the biologist Steven Rose (2001), does not agree with the name granted by Edelman of neural Darwinism. Rose believes that it is neither a homologous process nor sufficiently analogous to Darwinian natural selection. Considering neural Darwinism only as a metaphor (Rose 2001) Even Rose agrees with Francis Crick in calling it 'neural edelmism'.
Rose's strongest argument against neural Darwinism is that overproduction and subsequent selection of neurons and synapses, is actually a cooperative process rather than a process of competition. Migration of cells and axon growth over long distances is only possible by remote and local signals between the same neurons. On the contrary, if those signals are not present during the growing and migration period, then, the axon wouldn’t have reached its final destination. As far as cells do not "compete" between them, it can rather be seen as a "cooperative".
3.Evo-Devo: an extension to cognition
3.1.
Introduction
As we saw in the last chapter, when it relates to cognition, ontogeny does not actually recapitulate phylogeny, as Haeckel proposed in his “recapitulation theory” 5 (Gould, 1997). Now, it is necessary to discuss the relationship between embryological development and evolution of cognition, since embryos also evolve in different ways, putting the recapitulation theory seen as a historical side-note, rather than as a dogma in the field of developmental biology. Then, to understand the relationship between embryological development and evolution of cognition, we will explore the interdisciplinary field of research called Evolutionary developmental biology, also known as Evo-Devo.
Evo-Devo studies the differences between organisms during their development to determinate their phylogenetic relationships. Evo-Devo offers explanations about the phylogeny based on the heritability of their altered characters produced during the ontogeny of an organism. At the same time, Evo-Devo claims that the design of a character will not be totally predetermined by the genotype. In these terms, genes are not the only causal agents of development. At the same time, each developmental stage will react to multiple interactions between environmental and epigenetic factors. Evo-Devo does not question NS as an evolutionary force, but also delimit to what degree the NS can be considered as a creative force. When it relates to NS, one of the most controversial topics is the position of NS as a creative force or not. Against this position, authors such as Gould and Lewontin, argue that NS does not “create” features, adaptations, or even life. For them, NS it merely selects a feature that provides greater survival rates. On favor of this position we can find authors such as Ernst Mayr, who claimed NS as "an all-powerful natural selection".
Furthermore, all the processes related to the development of the brain plays an important role in the evolution of cognition. An Evo-Devo approach will allow us to specify how much weight developmental constraints have on evolutionary models of cognition. Recognizing that these constraints do not just limit, but also order the evolutionary path producing a bias of
5 The theory of recapitulation is commonly synthetize in a phrase given by Ernst Haeckel' as "ontogeny recapitulates phylogeny". This refers to a questioned biological hypothesis that argues that during the embryological development of an animal, from fertilization to gestation, i.e. ontogeny, all the successive stages from which the animal undergo represents stages in evolution of the animal's remote ancestors (phylogeny).
evolutionary phenomena that which cannot be explained by explicitly citing the classical evolutionary factors (eg, NS).
3.2 Evolutionary developmental biology theory
Nowadays, evolutionary developmental biology (Evo-Devo) theory studies: i) the evolution of development, by a comparative approach of features at different hierarchical levels (Hall, 2003);; ii) the establishment of homologies, by genetic expression patterns (Amundson, 2005);; iii) evolutionary innovations, to comprehend the mechanisms that give rise new characters (Hoekstra & Coyne, 2007);; iv) phenotypic evolutionary patterns, to determinate if development constraints can influence evolutive diversification (Müller, 2007);; and v) genotype-phenotype mapping, for the understanding of the dynamics of adaptation (Pigliucci, 2010).
However, the study of Evo-Devo as a discipline started in the 1980’s century, with the discovery of the homebox. In 1983, Walter Gehring from the University of Basel and Matthew Scott and Amy Weiner form the University of Indiana found a highly conserved 180-base pair (bp) DNA segment in animals, fungi and plants, involved in morphogenesis and which encodes a polypeptide segment designated as homeodomain (Gehring 1992). Later on, during the study of the development genetics of the fruit fly Drosophila, researchers found a coding sequence involved in segment formation. This sequence was found later along different species in clusters of related genes, now known as hox genes.
The study of homologous genes in different species ended up by sealing the connection between genetics, developmental biology and evolution. Despite the great conservation of genes, the morphological diversity between taxa is given by the variations in the expression of these genes. These variations would produce along the development morphological and functional differences between taxa on which NS would operate adapting the organisms to the environment and generating the enormous biodiversity past and present (Baguñá 2003). With this, scientist could not avoid the study of developmental genetics in terms of evolution, giving place to “Evo-Devo” (Carroll, 2008).
Evo-Devo theory claims that the genotype does not completely define the design of an organism, and it considers that mutations have a strong effect on fitness (Carroll, 2008). Within this theory, genes are not considered as the only causal agents of development. Moreover, the role of genes in development and evolution does not lie above that of the other
factors involve in such processes. Evo-Devo supporters believe that environmental and epigenetic factors bear equal importance as genes in the development of an organism (Balari & Lorenzo, 2008).
3.2.1 The neural system from an Evo-Devo perspective.
As we mentioned above, Evo-Devo claims that there are patterns involved during the development of organisms. However, these patterns are also found in the development of the nervous system. Nowadays, research has revealed the existence of different stages of brain formation, starting from a simple set of undifferentiated cells that grow and become the
neural plate, that will fold to form a groove then tube, open initially at each end. Three
projections come out of this tube. The first is the one that will give rise to the series of segments that make up the rhombencephalon, which will contribute to breathing, balance and keeping the body alert. The second segment will give rise to the mesencephalon, which coordinates additive and visual reflexes. Finally, the third will give rise to the precursor of the forebrain, responsible for reason and decision making (Nicholls et al., 2012).
In order to develop a nervous system, brain cells must specialize and migrate to their final locations, otherwise this will cause irreversible damages to the organism. Initially, only certain regions of the body are responsible for manufacturing cells in an "emergency" case, where by means of a cellular Darwinian strategy, those that have been able to integrate into a previously established and large system will be selected (Marcus, 2005).
Gene expression plays a very important role in terms of complexity, since they establish and adjust the neural circuits. So, we could say that the brain structure, as a cognitive substrate, is the result of transformations that occur during the development of an organism. Where the constrains6 of brain development enter the field of study of Evo-Devo. With this approach, it
will be possible to determine the weight of the causes of developmental constraints in evolutionary models of cognition such as the adaptation, described by Dennett, and ontogeny, described by Edelman. Due to the importance in the understanding and definition of developmental constraints in evolutionary developmental biology, we will revise in detail the constraints in the next subsection.
6 “Another consequence of interacting modules (in terms of the homebox) is that these interactions limit the
possible phenotypes that can be created, and they also allow change to occur in certain directions more easily than in others. Collectively, these restraints on phenotype production are called developmental constraints”.
