Varela – Chapter 9

Evolutionary Path Making and Natural Drift

The adaptationist stance

Adaptation (or Neo-Darwinism)

Adaptation is the centerpiece of evolutionary biology, just as representation is the centerpiece of most contemporary cognitive science

Neo-Darwinism:

• Evolution is a gradual modification of an organism by heredity in reproduction
• The heredity constantly diversifies (mutation, recombination)
• Natural selection is the mechanism that picks the optimal design

Modifications by small changes in heredity -> genes

Evolution = the totality of these small changes in interbreeding populations

Adaptation is the process linked to reproduction and survival = adapting

Evolution

The main task of evolution is to find sets of interrelated genes that can contribute to reproduction

If it improves reproduction, it improves its fitness

Fitness

Fitness as a measure of abundance (the effect of genes on the growth rate)

Problems:

• reproductive success depends on sexual encounters (in most animal groups)
• the effects of genes are intertwined, it is hard to pinpoint the effects of individual genes
• the milieu in which these genes act is varied and time dependent
• this milieu must be taken in the context of a life cycle and ecology of the animal

Fitness as a measure of persistence (probability of reproductive permanence over time)

The optimization is not the amount of offspring, but the probability of extinction

This approach is sensitive to long-term effects, but has the same measurement problems

Adaptationist stance

The process of natural selection is the main factor in organic evolution

Selective pressures act on the genetic variety of a population, producing changes over time according to an optimization of the fitness potential

Evolution as natural drift

“Evolution as natural drift is the biological counterpart of cognition as embodied action, and therefore also provides a more embracing theoretical context for the study of cognition as a biological phenomenon.” (p. 188)

Linkage and Pleiotropy

Presence of a gene does not result in an isolated trait (few exceptions, eye color)

Genic interdependence:

• the genome is not linear array of dependent genes
• it is comprised of a network of multiple reciprocal effects mediated through:
• repressors and depressors
• exons and introns
• jumping genes
• structural proteins

Punctuated equilibria:

• discontinuities in how species change over time
• transitions are global rearrangements involving cooperative effects and genetic exchanges
• intermediate forms in species cannot be imagined (no grey zone)

Pleiotropy provides difficulties for adaptatationism:

“Selection might push to decrease the frequency of a certain gene, but pleiotropy, on the other hand, might push to increase or maintain the gene. The net result is some compromise that cannot be described as simply the result of selective pressures” (p. 189)

Development

The development stage is as important as the final structure itself

Pattern formation and morphogenesis (shape/creation) are highly constrained cellular choreographies that delimit the possibilities for change

The larva model demonstrates that once again, emergent properties are important in a complex network

These emergent properties are referred to as intrinsic factors

It is important to not consider natural selection as being external and developmental constraints as internal, they are not opposed

Random Genetic Drift

It is widely recognized that there is a significant degree of random genetic drift

The source of this randomness is:

• Proximity of genes (the hitch-hiking effect)
• Sampling error (from generation to generation) read p. 191
• 40% of the genome is junk DNA (not expressed and repetitive)

Stasis

Groups survive with little change even though their environment changed drastically from our viewpoint

“Genotypic plasticity, which is at the base of evolutionary stasis, is also evident in the microbial world where constant genetic exchange occurs side by side with an astounding degree of stasis.” (p. 192)

Considering adaptation as a measure of abundance (because of this stasis) has nothing to do with long term survival

Makes more sense to approach adaptation as a measure of persistence

Units of Selection

The individual has been considered the only unit of evolution and selection

Theories including multiple levels or units working in parallel are plausible and explain phenomena that couldn’t be explained with single unit selection

Single unit:

• genes

Multiple units:

• DNA short sequences
• Genes
• Whole gene families
• Cells
• Species genome
• Individuals
• Groups of genes carried by different individuals
• Social group
• The interbreeding population
• The entire species
• The ecosystem of the interacting species
• The global biosphere

Beyond the Best in Evolution and Cognition

“To explain an observed biological regularity as an optimal fit or optimal correspondence with pregiven dimensions of the environment appears less and less tenable on both logical and empirical grounds.” (p. 193)

Evolutionary and cognitive issues coincide in 2 points:

• adaptive value of knowledge, explains the kind of cognition a species has today
• evolution is used as a source for theories and concepts in cognition

Representation in cognitive science is like adaptation in evolutionary theories, because optimality is the central point in both

The john buying a suit analogy brings up the point that a global situation needs to be considered

(p. 194)

Ecology and Development in Congruence

First step:

Switch from a prescriptive to a proscriptive logic

What is not allowed is forbidden to what is not forbidden is allowed

Natural selection in a proscriptive logic works in a modified way:

Selection discards what is not compatible with survival and reproduction

This opens the idea of a variety and diversity of evolution paths and biological structures

Second step:

Evolutionary process is satisficing instead of optimizing

Putting together parts in complicated arrays, not because it is the optimal design, but because it is a possible design

This again opens the idea of a variety of evolutionary paths

Evolution as Natural Drift (the authors point of view)

Four points (p. 196-197):

• The unit of evolution is a network capable of many different configurations
• Under structural coupling with a medium, these configurations generate selection, an ongoing process of satisficing that triggers change in the form of viable trajectories
• The specific trajectory is the interwoven result of multiple levels of subnetworks of selected self-organized repertoires
• Organism and medium are in a coimplicative relationship, they mutually specify each other

This view needs the applicability of these three conditions:

• Self-organizing capacities in biological networks
• Structural coupling
• Subnetworks of independent processes that interact with each other

The notion of the pregiven background is replaced by intrinsic factors

Richard Lewontin (p. 198)

The species brings forth and specifies its own domain of problems to be solved by satisficing

Living beings and their environment relate through mutual specification or codetermination

Environmental regularities are the result of a long history of codetermination

The organism is both the subject and the object of evolution.

Defining the enactive approach

Ontogeny: the development or developmental history of an individual organism

Phylogeny: the development or evolution of a particular group of organisms.

Structural Coupling: Structural coupling is the term for structure-determined (and structure- determining) engagement of a given unity with either its environment or another unity. The process of engagement which effects a "...history or recurrent interactions leading to the structural congruence between two (or more) systems" (Maturana & Varela, 1987, p. 75). It is ‘...a historical process leading to the spatio-temporal coincidence between the changes of state..’ (Maturana, 1975, p. 321) in the participants. As such, structural coupling has connotations of both coordination and co-evolution. (http://www.imprint.co.uk/thesaurus/structural_coupling.htm)

Cognition is no longer seen as problem solving on the basis of representation; instead, cognition in its most encompassing sense consists in the enactment or bringing forth of a world by a viable History of Structural Coupling. (p.205)

Such histories of coupling are not optimal (best or most favorable), but rather viable (capable of surviving or living successfully under certain environmental conditions).

Any action undertaken by the system is permitted as long as it does not violate the constraint of having to maintain the integrity of the system and/or its lineage. (p.205)

• There is always a next step for the system in its perceptually guided action
• The actions of the system are always directed toward situations that have yet to become actual.

Intentionality:

• Intentionality includes how system construes the world to be
• Intentionality includes how the world satisfies or fails to satisfy this construal.

Implications of this Intentionality:

• We can focus on the structure of the system by describing it as composed of various subsystems.
• We can focus on the behavioral interactions of the system by describing it as a unity capable of various forms of coupling.

What is Cognition?

Enaction: A history of structural coupling that brings forth a world. Through a network consisting of multiple levels of interconnected sensorimotor subnetworks.

It would be considered adequate when it either becomes part of an ongoing existing world (as the young of every species do, or shapes a new one (as happens in evolutionary history).

Enactive Cognitive Science

Brook’s “Intelligence without representation”:

Representation is the wrong unit of abstraction in building the bulkiest parts of intelligence system. (p. 208)

The goal is not the usual decomposition of a system by functioning but rather by activity. (p.209)

Activity: Pattern of interaction with the world. Each activity can at least post facto be rationalized as pursuing some purpose. (p.211)

Layer: activity, producing subsystem.

There need be no distinction between a “perception subsystem,” a “central system” and an action system.”

There are no representations involved in the layers of Brooks’ Model.

Paul Smolensky’s Harmony theory:

• Exogenous (derived or developed from outside the body) features in the task domain corresponds to pregiven features of the world
• Endogenous (growing or developing from within) activity in the network acquires through experience an abstract meaning that optimally encodes environmental regularity.

The enactive program requires that we eschew any form of optimal fitness by taking this kind of cognitive system into a situation where endogenous and exogenous features are mutually definitory over a prolonged history that requires only a viable coupling. (p. 213)