Transcript Chapter 4: The Origin of Mind

Chapter 4: The Origin of
Mind
Evolution and
Development of Brain
and Cognition
Controversy
Controversy
over the evolution of the
human mind and brain has raged since
naturalists began debating the implications
of Darwin’s and Wallace’s first publication
regarding natural selection, which was
presented in 1858 and later proved in
Darwin’s Origin of Species in 1859.
Controversy
 Disagreement
 Darwin:
between Darwin and Wallace:
metal faculties of the human brain, such as
language, had evolved by means of natural and sexual
selection and, although qualitatively different in some
ways, showed many continuities with the faculties of mind
and brain of other species.
 Wallace: did not believe that this could be true,
especially as related to intelligence and morality, which
according to Wallace, could not be the result of such
mindless organic evolution.
Current Debate
 Still
concerns whether the human mind and brain are
composed of specific faculties, now called modules,
that evolved as a result of specific selection pressures.
 The debate is regarding the relative importance of
inherent gene-driven constraints versus patterns of
developmental experience on the organization and
functioning of human mental faculties, such as
language.
 Epigenisis
 Plasticity
Current Debate
Concerned
with the extent to which
inherent constraints or developmental
experiences are emphasized. Two views:
High
degree of inherent constraint
Mental faculties emerge through an
interaction of more minimal inherent
constraints and the potent effects of
developmental experience
Focus
The
focus of arguments by scientists
at either end focus on the benefits
of inherent constraint or openness to
experiential modification.
Author’s proposal: faculties of mind
are the result of specific selection
pressures.
Variant vs. Invariant Patterns
(author’s proposal continued)
 Some
of these information patterns, such as shape
of face, are largely the same (invariant patterns)
from one situation or generation to the next, and
thus constrained brain and cognitive systems that
direct attention to and process these patterns are
predicted to evolve.
 For some information patterns individual
differences (variant patterns) is essential. (ex:
the ability to distinguish the cry of one’s own baby
from the cry of all other babies.).
Constraints on Brain Organization
Across Species
 Shows
how the human brain can show continuities
with the brains of other species and yet be
different in ways that are uniquely human.
 This provides a framework for understanding how
evolution can operate on brain systems that are
common across species (due to a common ancestor)
to create species-specific specializations, such as
those things that Wallace argued sets humans
apart from all other species (intelligence and
morality).
Constraints on Brain Organization
Across Species
 Extant
species=species whose lines have branched
off of the evolutionary tree at different points in
evolutionary history (provide the best means to
make inferences about the history of brain
organization and evolution)
 In mammalian evolution, three major lines have
emerged:
 Prototheria (extant example: duck-billed platypus)
 Metatheria (extant example: eastern gray kangaroo)
 Eutheria (placental mammals--extant example: human
beings)
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.
Constraints on Brain Organizations
Across Species



Analogous: same function but independent evolution
Homology: similarity because of a common ancestor.
Scientists examine brain organization of extant species in an
attempt to deduce similarities (constraints conserved from a
common ancestor) and differences (species-specific adaptations).
Constraints: (examples)







Structure of the central nervous system (CNS)
Diencephalon (including the thalamus and hypothalamus)
The organization of the thalamus
Many of the sensory nuclei of the thalamus
Homologous nuclei found when comparing a mouse and human thalamus
Many divisions of the hippocampus
Also in the neocortex (primary sensory areas--primary visual,
somatosensory, and auditory corticles)
Constraints on Brain Organization
Across Species
 The
pattern emerging from research is that the
basic architecture and some of the specialized
functions of the mammalian neocortex and
subcortical regions are conserved across species,
including humans.--inconsistent with Wallace’s
position that the brain and mind of humans is
fundamentally different from those of other
species.
How are Human Brains Different
from Other Species?






The number of genes responsible for the development of the human
brain
Studies also suggest that the same genes may be expressed
differently
Humans also show a much higher frequency of gene expression.
Therefore, humans show higher rates of neuronal and related
activities
An analysis in which 7, 645 genes in the mouse, chimpanzee, and
human were compared, found evidence for natural selection
modifying a set of specific genes involved in neural development,
speech, and hearing, among other traits, during human evolution.
Concluding: Many of the same genes that regulate the building of
the human brain are involved in the building of other brains, but
there are also important species-specific differences.
Brain Development is Dependent on
Both Intrinsic and Extrinsic Factors
 The
human neocortex is subdivided into many
functionally and architectonically distinct areas.
Arealization refers to the prenatal formation of
these areas.
 Intrinsic: belonging naturally; essential.
 Extrinsic: not part of the essential nature of
someone or something; coming or operating from
outside.
 Protomap Hypothesis
 Protocortex Hypothesis
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 vs. Extrinsic Model
 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 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.
Allometry
 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 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.
Allometric 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)
 Other
Other factors
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




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 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 experiencedriven modification)
Exoskeleton





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.