Chapter 4: The Origin of Chapter 4: The Origin of MindMind

Chapter 4: The Origin of Chapter 4: The Origin of MindMind

Evolution and Evolution and Development of Brain Development of Brain

and Cognitionand Cognition

Evolution and Evolution and Development of Brain Development of Brain

and Cognitionand Cognition

ControversyControversyControversyControversy

Controversy over the evolution of the Controversy over the evolution of the human mind and brain has raged since human mind and brain has raged since naturalists began debating the naturalists began debating the implications of Darwin’s and Wallace’s implications of Darwin’s and Wallace’s first publication regarding natural first publication regarding natural selection, which was presented in 1858 selection, which was presented in 1858 and later proved in Darwin’s and later proved in Darwin’s Origin of Origin of SpeciesSpecies in 1859. in 1859.

Controversy over the evolution of the Controversy over the evolution of the human mind and brain has raged since human mind and brain has raged since naturalists began debating the naturalists began debating the implications of Darwin’s and Wallace’s implications of Darwin’s and Wallace’s first publication regarding natural first publication regarding natural selection, which was presented in 1858 selection, which was presented in 1858 and later proved in Darwin’s and later proved in Darwin’s Origin of Origin of SpeciesSpecies in 1859. in 1859.

ControversyControversyControversyControversy

Disagreement between Darwin and Wallace:Disagreement between Darwin and Wallace: DarwinDarwin: metal faculties of the human brain, such as : metal faculties of the human brain, such as

language, had evolved by means of natural and language, had evolved by means of natural and sexual selection and, although qualitatively different sexual selection and, although qualitatively different in some ways, showed many continuities with the in some ways, showed many continuities with the faculties of mind and brain of other species.faculties of mind and brain of other species.

WallaceWallace: did not believe that this could be true, : did not believe that this could be true, especially as related to intelligence and morality, especially as related to intelligence and morality, which according to Wallace, could not be the result which according to Wallace, could not be the result of such mindless organic evolution.of such mindless organic evolution.

Disagreement between Darwin and Wallace:Disagreement between Darwin and Wallace: DarwinDarwin: metal faculties of the human brain, such as : metal faculties of the human brain, such as

language, had evolved by means of natural and language, had evolved by means of natural and sexual selection and, although qualitatively different sexual selection and, although qualitatively different in some ways, showed many continuities with the in some ways, showed many continuities with the faculties of mind and brain of other species.faculties of mind and brain of other species.

WallaceWallace: did not believe that this could be true, : did not believe that this could be true, especially as related to intelligence and morality, especially as related to intelligence and morality, which according to Wallace, could not be the result which according to Wallace, could not be the result of such mindless organic evolution.of such mindless organic evolution.

Current Debate Current Debate Current Debate Current Debate Still concerns whether the human mind and brain are Still concerns whether the human mind and brain are

composed of specific faculties, now called composed of specific faculties, now called modulesmodules, , that evolved as a result of specific selection that evolved as a result of specific selection pressures.pressures.

The debate is regarding the relative importance of The debate is regarding the relative importance of inherent gene-driven constraints versus patterns of inherent gene-driven constraints versus patterns of developmental experience on the organization and developmental experience on the organization and functioning of human mental faculties, such as functioning of human mental faculties, such as language.language.

EpigenisisEpigenisis PlasticityPlasticity

Still concerns whether the human mind and brain are Still concerns whether the human mind and brain are composed of specific faculties, now called composed of specific faculties, now called modulesmodules, , that evolved as a result of specific selection that evolved as a result of specific selection pressures.pressures.

The debate is regarding the relative importance of The debate is regarding the relative importance of inherent gene-driven constraints versus patterns of inherent gene-driven constraints versus patterns of developmental experience on the organization and developmental experience on the organization and functioning of human mental faculties, such as functioning of human mental faculties, such as language.language.

EpigenisisEpigenisis PlasticityPlasticity

Current DebateCurrent DebateCurrent DebateCurrent Debate

Concerned with the extent to which Concerned with the extent to which inherent constraints or developmental inherent constraints or developmental experiences are emphasized. experiences are emphasized. Two Two viewsviews:: High degree of inherent constraintHigh degree of inherent constraint Mental faculties emerge through an Mental faculties emerge through an

interaction of more minimal inherent interaction of more minimal inherent constraints and the potent effects of constraints and the potent effects of developmental experiencedevelopmental experience

Concerned with the extent to which Concerned with the extent to which inherent constraints or developmental inherent constraints or developmental experiences are emphasized. experiences are emphasized. Two Two viewsviews:: High degree of inherent constraintHigh degree of inherent constraint Mental faculties emerge through an Mental faculties emerge through an

interaction of more minimal inherent interaction of more minimal inherent constraints and the potent effects of constraints and the potent effects of developmental experiencedevelopmental experience

FocusFocusFocusFocus

The focus of arguments by scientists The focus of arguments by scientists at either end focus on the benefits at either end focus on the benefits of inherent constraint or openness of inherent constraint or openness to experiential modification. to experiential modification.

Author’s proposalAuthor’s proposal: faculties of mind : faculties of mind are the result of specific selection are the result of specific selection pressures. pressures.

The focus of arguments by scientists The focus of arguments by scientists at either end focus on the benefits at either end focus on the benefits of inherent constraint or openness of inherent constraint or openness to experiential modification. to experiential modification.

Author’s proposalAuthor’s proposal: faculties of mind : faculties of mind are the result of specific selection are the result of specific selection pressures. pressures.

Variant vs. Invariant PatternsVariant vs. Invariant Patterns (author’s proposal continued) (author’s proposal continued)Variant vs. Invariant PatternsVariant vs. Invariant Patterns (author’s proposal continued) (author’s proposal continued)

Some of these information patterns, such as Some of these information patterns, such as shape of face, are largely the same (invariant shape of face, are largely the same (invariant patterns) from one situation or generation to the patterns) from one situation or generation to the next, and thus constrained brain and cognitive next, and thus constrained brain and cognitive systems that direct attention to and process systems that direct attention to and process these patterns are predicted to evolve.these patterns are predicted to evolve.

For some information patterns individual For some information patterns individual differences (variant patterns) is essential. (ex: differences (variant patterns) is essential. (ex: the ability to distinguish the cry of one’s own the ability to distinguish the cry of one’s own baby from the cry of all other babies.). baby from the cry of all other babies.).

Some of these information patterns, such as Some of these information patterns, such as shape of face, are largely the same (invariant shape of face, are largely the same (invariant patterns) from one situation or generation to the patterns) from one situation or generation to the next, and thus constrained brain and cognitive next, and thus constrained brain and cognitive systems that direct attention to and process systems that direct attention to and process these patterns are predicted to evolve.these patterns are predicted to evolve.

For some information patterns individual For some information patterns individual differences (variant patterns) is essential. (ex: differences (variant patterns) is essential. (ex: the ability to distinguish the cry of one’s own the ability to distinguish the cry of one’s own baby from the cry of all other babies.). baby from the cry of all other babies.).

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

Shows how the human brain can show Shows how the human brain can show continuities with the brains of other species and continuities with the brains of other species and yet be different in ways that are uniquely yet be different in ways that are uniquely human.human.

This provides a framework for understanding This provides a framework for understanding how evolution can operate on brain systems how evolution can operate on brain systems that are common across species (due to a that are common across species (due to a common ancestor) to create species-specific common ancestor) to create species-specific specializations, such as those things that specializations, such as those things that Wallace argued sets humans apart from all Wallace argued sets humans apart from all other species (intelligence and morality).other species (intelligence and morality).

Shows how the human brain can show Shows how the human brain can show continuities with the brains of other species and continuities with the brains of other species and yet be different in ways that are uniquely yet be different in ways that are uniquely human.human.

This provides a framework for understanding This provides a framework for understanding how evolution can operate on brain systems how evolution can operate on brain systems that are common across species (due to a that are common across species (due to a common ancestor) to create species-specific common ancestor) to create species-specific specializations, such as those things that specializations, such as those things that Wallace argued sets humans apart from all Wallace argued sets humans apart from all other species (intelligence and morality).other species (intelligence and morality).

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

Extant species=species whose lines have Extant species=species whose lines have branched off of the evolutionary tree at branched off of the evolutionary tree at different points in evolutionary history (provide different points in evolutionary history (provide the best means to make inferences about the the best means to make inferences about the history of brain organization and evolution)history of brain organization and evolution)

In mammalian evolution, In mammalian evolution, three major lines three major lines have emerged:have emerged: PrototheriaPrototheria (extant example: duck-billed platypus) (extant example: duck-billed platypus) MetatheriaMetatheria (extant example: eastern gray kangaroo) (extant example: eastern gray kangaroo) EutheriaEutheria (placental mammals--extant example: (placental mammals--extant example:

human beings)human beings)

Extant species=species whose lines have Extant species=species whose lines have branched off of the evolutionary tree at branched off of the evolutionary tree at different points in evolutionary history (provide different points in evolutionary history (provide the best means to make inferences about the the best means to make inferences about the history of brain organization and evolution)history of brain organization and evolution)

In mammalian evolution, In mammalian evolution, three major lines three major lines have emerged:have emerged: PrototheriaPrototheria (extant example: duck-billed platypus) (extant example: duck-billed platypus) MetatheriaMetatheria (extant example: eastern gray kangaroo) (extant example: eastern gray kangaroo) EutheriaEutheria (placental mammals--extant example: (placental mammals--extant example:

human beings)human beings)

A COMMON BRAIN DIVISION

A COMMON BRAIN DIVISION

Also called the cerebral cortex, the neocortex constitutes five-sixths of the human brain. It is the outer portion of our brain, and is approximately the size of a newspaper page crumpled together.

Also called the cerebral cortex, the neocortex constitutes five-sixths of the human brain. It is the outer portion of our brain, and is approximately the size of a newspaper page crumpled together.

Constraints on Brain Constraints on Brain Organizations Across SpeciesOrganizations Across Species

Constraints on Brain Constraints on Brain Organizations Across SpeciesOrganizations Across Species

AnalogousAnalogous: same function but independent evolution: same function but independent evolution HomologyHomology: similarity because of a common ancestor.: similarity because of a common ancestor. Scientists examine brain organization of extant species in an Scientists examine brain organization of extant species in an

attempt to deduce similarities (constraints conserved from a attempt to deduce similarities (constraints conserved from a common ancestor) and differences (species-specific common ancestor) and differences (species-specific adaptations). adaptations). ConstraintsConstraints: (examples): (examples) Structure of the central nervous system (CNS)Structure of the central nervous system (CNS) Diencephalon (including the thalamus and hypothalamus) Diencephalon (including the thalamus and hypothalamus) The organization of the thalamusThe organization of the thalamus Many of the sensory nuclei of the thalamusMany of the sensory nuclei of the thalamus Homologous nuclei found when comparing a mouse and human Homologous nuclei found when comparing a mouse and human

thalamusthalamus Many divisions of the hippocampusMany divisions of the hippocampus Also in the neocortex (primary sensory areas--primary visual, Also in the neocortex (primary sensory areas--primary visual,

somatosensory, and auditory corticles)somatosensory, and auditory corticles)

AnalogousAnalogous: same function but independent evolution: same function but independent evolution HomologyHomology: similarity because of a common ancestor.: similarity because of a common ancestor. Scientists examine brain organization of extant species in an Scientists examine brain organization of extant species in an

attempt to deduce similarities (constraints conserved from a attempt to deduce similarities (constraints conserved from a common ancestor) and differences (species-specific common ancestor) and differences (species-specific adaptations). adaptations). ConstraintsConstraints: (examples): (examples) Structure of the central nervous system (CNS)Structure of the central nervous system (CNS) Diencephalon (including the thalamus and hypothalamus) Diencephalon (including the thalamus and hypothalamus) The organization of the thalamusThe organization of the thalamus Many of the sensory nuclei of the thalamusMany of the sensory nuclei of the thalamus Homologous nuclei found when comparing a mouse and human Homologous nuclei found when comparing a mouse and human

thalamusthalamus Many divisions of the hippocampusMany divisions of the hippocampus Also in the neocortex (primary sensory areas--primary visual, Also in the neocortex (primary sensory areas--primary visual,

somatosensory, and auditory corticles)somatosensory, and auditory corticles)

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

Constraints on Brain Constraints on Brain Organization Across SpeciesOrganization Across Species

The pattern emerging from research is that the The pattern emerging from research is that the basic architecture and some of the specialized basic architecture and some of the specialized functions of the mammalian neocortex and functions of the mammalian neocortex and subcortical regions are conserved across subcortical regions are conserved across species, including humans.--inconsistent with species, including humans.--inconsistent with Wallace’s position that the brain and mind of Wallace’s position that the brain and mind of humans is fundamentally different from those humans is fundamentally different from those of other species. of other species.

The pattern emerging from research is that the The pattern emerging from research is that the basic architecture and some of the specialized basic architecture and some of the specialized functions of the mammalian neocortex and functions of the mammalian neocortex and subcortical regions are conserved across subcortical regions are conserved across species, including humans.--inconsistent with species, including humans.--inconsistent with Wallace’s position that the brain and mind of Wallace’s position that the brain and mind of humans is fundamentally different from those humans is fundamentally different from those of other species. of other species.

How are Human Brains Different How are Human Brains Different from Other Species?from Other Species?

How are Human Brains Different How are Human Brains Different from Other Species?from Other Species?

The number of genes responsible for the development of the The number of genes responsible for the development of the human brainhuman brain

Studies also suggest that the same genes may be expressed Studies also suggest that the same genes may be expressed differentlydifferently

Humans also show a much higher frequency of gene expression.Humans also show a much higher frequency of gene expression. Therefore, humans show higher rates of neuronal and related Therefore, humans show higher rates of neuronal and related

activitiesactivities An analysis in which 7, 645 genes in the mouse, chimpanzee, and An analysis in which 7, 645 genes in the mouse, chimpanzee, and

human were compared, found evidence for natural selection human were compared, found evidence for natural selection modifying a set of specific genes involved in neural development, modifying a set of specific genes involved in neural development, speech, and hearing, among other traits, during human evolution.speech, and hearing, among other traits, during human evolution.

ConcludingConcluding: Many of the same genes that regulate the building of : Many of the same genes that regulate the building of the human brain are involved in the building of other brains, but the human brain are involved in the building of other brains, but there are also important species-specific differences.there are also important species-specific differences.

The number of genes responsible for the development of the The number of genes responsible for the development of the human brainhuman brain

Studies also suggest that the same genes may be expressed Studies also suggest that the same genes may be expressed differentlydifferently

Humans also show a much higher frequency of gene expression.Humans also show a much higher frequency of gene expression. Therefore, humans show higher rates of neuronal and related Therefore, humans show higher rates of neuronal and related

activitiesactivities An analysis in which 7, 645 genes in the mouse, chimpanzee, and An analysis in which 7, 645 genes in the mouse, chimpanzee, and

human were compared, found evidence for natural selection human were compared, found evidence for natural selection modifying a set of specific genes involved in neural development, modifying a set of specific genes involved in neural development, speech, and hearing, among other traits, during human evolution.speech, and hearing, among other traits, during human evolution.

ConcludingConcluding: Many of the same genes that regulate the building of : Many of the same genes that regulate the building of the human brain are involved in the building of other brains, but the human brain are involved in the building of other brains, but there are also important species-specific differences.there are also important species-specific differences.

Brain Development is Dependent on Brain Development is Dependent on Both Intrinsic and Extrinsic FactorsBoth Intrinsic and Extrinsic Factors

Brain Development is Dependent on Brain Development is Dependent on Both Intrinsic and Extrinsic FactorsBoth Intrinsic and Extrinsic Factors

The human neocortex is subdivided into many The human neocortex is subdivided into many functionally and architectonically distinct functionally and architectonically distinct areas. areas. Arealization Arealization refers to the prenatal refers to the prenatal formation of these areas.formation of these areas.

IntrinsicIntrinsic: belonging naturally; essential.: belonging naturally; essential. ExtrinsicExtrinsic: not part of the essential nature of : not part of the essential nature of

someone or something; coming or operating someone or something; coming or operating from outside.from outside. Protomap HypothesisProtomap Hypothesis Protocortex HypothesisProtocortex Hypothesis

The human neocortex is subdivided into many The human neocortex is subdivided into many functionally and architectonically distinct functionally and architectonically distinct areas. areas. Arealization Arealization refers to the prenatal refers to the prenatal formation of these areas.formation of these areas.

IntrinsicIntrinsic: belonging naturally; essential.: belonging naturally; essential. ExtrinsicExtrinsic: not part of the essential nature of : not part of the essential nature of

someone or something; coming or operating someone or something; coming or operating from outside.from outside. Protomap HypothesisProtomap Hypothesis Protocortex HypothesisProtocortex Hypothesis

Intrinsic Model vs. Extrinsic Model

Intrinsic Model vs. Extrinsic Model

Intrinsic Model: consistent with the Protomap Hypothesis. Recent results have shown that the developing neocortex is “patterned” early in development, with a graded expression of different genes in different cortical areas. (ex: gene expression patterns are found in mice lacking thalmacortical inputs, suggesting that some degree of cortical arealization may occur without external, thalamic input).

FG28 Emerging evidence seems to suggest that the largely prenatal

development of the neocortex, is at least to some extent dependent on intrinsic, genetically mediated properties of the neocortex.

Intrinsic Model: consistent with the Protomap Hypothesis. Recent results have shown that the developing neocortex is “patterned” early in development, with a graded expression of different genes in different cortical areas. (ex: gene expression patterns are found in mice lacking thalmacortical inputs, suggesting that some degree of cortical arealization may occur without external, thalamic input).

FG28 Emerging evidence seems to suggest that the largely prenatal

development of the neocortex, is at least to some extent dependent on intrinsic, genetically mediated properties of the neocortex.

Intrinsic Model vs. Extrinsic Intrinsic Model vs. Extrinsic ModelModel

Intrinsic Model vs. Extrinsic Intrinsic Model vs. Extrinsic ModelModel

Extrinsic Model: consistent with the Protocortex Hypothesis. Intrinsic influences are not the whole story. When cells from the location of the visual cortex--presumably destined to be visual cells--are transplanted into the developing somatosensory cortex, these cells develop into cells that are common in the somatosensory cortex.

This evidence suggests that input from the thalamus and synaptic activity play a major role in the determination of organization of the neocortex.

Extrinsic Model: consistent with the Protocortex Hypothesis. Intrinsic influences are not the whole story. When cells from the location of the visual cortex--presumably destined to be visual cells--are transplanted into the developing somatosensory cortex, these cells develop into cells that are common in the somatosensory cortex.

This evidence suggests that input from the thalamus and synaptic activity play a major role in the determination of organization of the neocortex.

Intrinsic vs. Extrinsic ModelIntrinsic vs. Extrinsic Model

Most developmental neurobiologists now agree that normal and largely prenatal (in most species) development of the neocortex appears to depend on both internal (graded gene expression across areas of neocortex) and external (inputs from the thalamus) influences.

Most developmental neurobiologists now agree that normal and largely prenatal (in most species) development of the neocortex appears to depend on both internal (graded gene expression across areas of neocortex) and external (inputs from the thalamus) influences.

AllometryAllometry Allometry: refers to systematic relations among

different features of body morphology, architecture, and development; relations that complicate the determination of whether any particular trait is the direct result of specific selection pressures.

A more central issue is the potential for allometric relationships among different regions of the brain, specifically whether selection that operated to increase the size of one brain area could result in increases in the size of other areas. (relation to brain plasticity)

Allometry: refers to systematic relations among different features of body morphology, architecture, and development; relations that complicate the determination of whether any particular trait is the direct result of specific selection pressures.

A more central issue is the potential for allometric relationships among different regions of the brain, specifically whether selection that operated to increase the size of one brain area could result in increases in the size of other areas. (relation to brain plasticity)

Allometric ExpansionAllometric Expansion When the relations were analyzed among the absolute size of 12

brain regions across 131 species of mammal, they found that a single factor accounted for 96% of the similarities in region size. Results for this factor suggest that a single mechanism may account for the absolute size of many different brain regions and thus provide evidence inconsistent with the position that there are specific faculties of brain and mind that evolved as a result of specific social or ecological selection pressures.

Finlay and Darlington conceded that specific brain and cognitive adaptations are found, but they appear to be less important than a more general mechanism that influenced the evolution of the absolute size of all brain regions. The proposed mechanism involves genes regulating prenatal neocortical development.

When the relations were analyzed among the absolute size of 12 brain regions across 131 species of mammal, they found that a single factor accounted for 96% of the similarities in region size. Results for this factor suggest that a single mechanism may account for the absolute size of many different brain regions and thus provide evidence inconsistent with the position that there are specific faculties of brain and mind that evolved as a result of specific social or ecological selection pressures.

Finlay and Darlington conceded that specific brain and cognitive adaptations are found, but they appear to be less important than a more general mechanism that influenced the evolution of the absolute size of all brain regions. The proposed mechanism involves genes regulating prenatal neocortical development.

Allometric ExpansionAllometric Expansion

A several fold increase in the size of the neocortex could occur as a result of genetic changes that prolonged the division of the progenitor cell that give birth to neurons, which could significantly increase the size of the neocortex in the absence of specific selection pressures. (talked about in chapter 3)

A several fold increase in the size of the neocortex could occur as a result of genetic changes that prolonged the division of the progenitor cell that give birth to neurons, which could significantly increase the size of the neocortex in the absence of specific selection pressures. (talked about in chapter 3)

Other factorsOther factors Other scientists analyzed systems of brain

regions that often operate together--cerebrotypes--to determine if these integrated systems were related to identifiable social or ecological conditions, such as demands associated with prey capture.

Using this approach they found that distinct cerebrotypes emerged for species of insectivore, shrew, and primate and were consistent with adaptations to specific ecological and social conditions.

Other scientists analyzed systems of brain regions that often operate together--cerebrotypes--to determine if these integrated systems were related to identifiable social or ecological conditions, such as demands associated with prey capture.

Using this approach they found that distinct cerebrotypes emerged for species of insectivore, shrew, and primate and were consistent with adaptations to specific ecological and social conditions.

Costs and Results of Allometric Expansion of the Neocortex

Costs and Results of Allometric Expansion of the Neocortex

Expansion of brain size results in higher basal metabolic costs, consuming about 20% of calories in the average human.

Dendrites that are doubled in length must be quadrupled in diameter.

With cortical expansions, each neuron must communicate with proportionally fewer neurons than before the expansion.

Specializations associated with cortical expansion confer benefits such as increased specialization of neuronal circuits and a corresponding increase in the fidelity of information the region can process and an increased ability to integrate information within and across areas.

Expansion of brain size results in higher basal metabolic costs, consuming about 20% of calories in the average human.

Dendrites that are doubled in length must be quadrupled in diameter.

With cortical expansions, each neuron must communicate with proportionally fewer neurons than before the expansion.

Specializations associated with cortical expansion confer benefits such as increased specialization of neuronal circuits and a corresponding increase in the fidelity of information the region can process and an increased ability to integrate information within and across areas.

Constraints and Experiential Modification Working TogetherConstraints and Experiential

Modification Working Together Research suggests that brain organization and most functions of

mind are dependent on a mix of gene-driven constraints and patterns of early experiences. Example: The basic pattern of the human face is invariant, and thus

inherent constraints on the brain and cognitive systems that are sensitive to these patterns are predicted to evolve, because these constraints would enable the fast, efficient identification of conspecifics (e.g., parents).

Sexual reproduction, mutations, and development perturbations (e.g., poor nutrition) result in variation around this basic pattern. Systems associated with sensitivity to variation must inevitably be plastic, as a new cohort of individuals is produced each generation. (combination of inherent constraint and openness to experience-driven modification)

Research suggests that brain organization and most functions of mind are dependent on a mix of gene-driven constraints and patterns of early experiences. Example: The basic pattern of the human face is invariant, and thus

inherent constraints on the brain and cognitive systems that are sensitive to these patterns are predicted to evolve, because these constraints would enable the fast, efficient identification of conspecifics (e.g., parents).

Sexual reproduction, mutations, and development perturbations (e.g., poor nutrition) result in variation around this basic pattern. Systems associated with sensitivity to variation must inevitably be plastic, as a new cohort of individuals is produced each generation. (combination of inherent constraint and openness to experience-driven modification)

ExoskeletonExoskeleton Exoskeleton= refers to inherent constraints on the types of

information the organism attends to and processes. It is a type of plasticity. The absolute boundaries are determined by the basic physics of information conduction, with constraints for individual species falling within this range.

Plasticity occurs within the constraints of the exoskeleton, and the associated “soft” mechanisms would evolve for species and domains in which within-category discriminations result in survival or reproductive advantage.

Exoskeleton= hard, set, inherent constraints. “soft”= within these hard, set, constraints, there is moldable

plasticity. Metaphor= description of the interaction of constraints and

experiential modification in human mental processes.

Exoskeleton= refers to inherent constraints on the types of information the organism attends to and processes. It is a type of plasticity. The absolute boundaries are determined by the basic physics of information conduction, with constraints for individual species falling within this range.

Plasticity occurs within the constraints of the exoskeleton, and the associated “soft” mechanisms would evolve for species and domains in which within-category discriminations result in survival or reproductive advantage.

Exoskeleton= hard, set, inherent constraints. “soft”= within these hard, set, constraints, there is moldable

plasticity. Metaphor= description of the interaction of constraints and

experiential modification in human mental processes.