Selection and Change: Biology and Behavior AILUN – Lecture 4 S. Glenn - AILUN 2008

Process and Content in Scientific Explanation Content in Science – The phenomena of interest (e.g. movements of heavenly bodies, composition of matter, differences in species, child’s head-banging) – That which the scientific method is used to understand and explain – Begins with everyday observation but often ends with terms derived from identifying process Process in Science – Mechanisms or forces that explain observed phenomena (natural selection, reinforcement, gravity) – Usually describe functional relations among classes – Virtually always entails a different way of classifying (e.g. operants) as natural lines of fracture are identified – Early description of processes often lead to new concepts (e.g. genes) S. Glenn - AILUN 2008

Examples of Process and Content in Biology and Learned Behavior Selection Process DomainContent (Results of Selection Process) Natural selection Living things E. coli D. melanogaster Operant selection Learned behavior Rat #1’s leverpressing Ricardo’s cake baking S. Glenn - AILUN 2008

Variation among Organisms of a Biological Population (Species) in a Specific Environment S. Glenn - AILUN 2008 Individual organisms of a moth species vary in features (color/size) Successive populations exist in an unchanging environment in which all features are equally adapted The contingent relation between the moths and their environment is stable and the population is in a relatively steady state Time 1Time 2Time 3Time 4

Change in Selection Contingencies S. Glenn - AILUN 2008 Environment gradually changes Contingencies of survival increasingly favor darker moths Lineage that began with mostly white moths at Time 1 has mostly black moths at Time 4 Time 1Time 2Time 3Time 4

Some Results of Natural Selection 1 Changes over time in properties of organisms of a species – Successive populations become on average larger, smaller, darker, lighter, etc. Speciation or splitting of lineages into daughter species with different evolutionary trajectories – Common ancestor species of humans and bonobo chimps has descendants of different species Organisms in some lineages become structurally more complex – Single cell -> multiple cells – Differentiation of cellular functions – Organs and their functional interrelations Organisms in some lineages become functionally more complex – More parts of the physical environment affect survival/reproduction – More parts of the organism are involved in behavior – Behavior has more effects on the environment Relations among natural populations (ecologies) become increasingly complex S. Glenn - AILUN 2008

Variants of an Operant Population in a Specific Environment S. Glenn - AILUN 2008 Individual keypecks of a pigeon vary in many features, including IRT lengths These pecks occur in an environment where pecking produces food on a VI 4 min schedule Is there a relation between IRT lengths and the contingency? VI-4 min

Selection in an Operant Population S. Glenn - AILUN 2008 Change the selection contingency so that reinforcement is on FR-30 schedule and the population evolves IRTs becoming increasingly concentrated at.7 “ and.4” over 50 min after abrupt change in selecting environment 2 Figure from Blough, 1963 VI-4 min FR

Some Results of Operant Selection Changes over time in properties of responses in an operant lineage – Ex: IRTs become much shorter Origin of new operants in a repertoire – Ex: Shaping of leverpress Increasing complexity of behavioral occurrences – Ex: Baking a cake becomes a functional unit Increasing numbers of stimulus control relations – Ex: Distinction between Uncle B and Uncle S – Ex: Distinction between species of spider S. Glenn - AILUN 2008

The Effect of Operant Selection on Complexity of Learned Behavior The behavioral instances of a lineage become more complex in organization as lineages split and evolve – Single component responses -> chains and modular units – Response differentiation and diverging lineages – Modular units become functionally interrelated Operants relate to environment in more ways – More parts of the physical environment become controlling variables (discrimination, generalization, conditional control, etc.) – More parts of the organism are involved in behavior – Behavior causes increasingly greater changes in the environment Result is a web of interrelations among behavioral units in an individual repertoire S. Glenn - AILUN 2008

Toward A General Account Selection may account for change in multiple domains and each domain is distinguished by the locus of its content – Biological evolution is gene-based and its lineages (species) are localized in biospheres – Operant learning is neuron-based and lineages (operants) are localized within individual organisms – Cultural evolution is operant-based and lineages are localized in social groups of behaviorally-related organisms Selectionist theory in each domain is built on the concepts particular to that domain A general account moves the scientific language of specific domains to a meta-language that can apply to multiple domains Process terms of a general account must apply to all levels of organization S. Glenn - AILUN 2008

Class Terms Suggested by David Hull for A General Account of Selection Natural KindsFunctionEffect InteractorsInteract differentially with environment Differential replication ReplicatorsPass traits to next generation Change in trait frequencies of lineage LineagesRetain effects on population of previous selection cycles Evolution (change over time in characteristics of a natural population) S. Glenn - AILUN 2008

A General (Content Free) Account of Selection 3 A ‘natural population’ of entities exists in space/time Entities in the population must have a common origin (are related by ‘descent’) Entities constituting the population must vary in ‘inherited’ traits or characteristics Differential interactions of entities with their environment causes differential replication of some traits over others (selection) Differential replication results in change in frequency of inherited traits in the natural population Locus of evolution is in the changing natural populations that constitute a lineage S. Glenn - AILUN 2008

Summary Content of a scientific domain is what is to be explained Processes are described that designed to explain the content Selection is explanatory concept in biological evolution and operant learning A general account of selection will use class terms that subsume concepts in all domains to which the account applies S. Glenn - AILUN 2008

References 1Mayr, E. (1982). The growth of biological thought. Cambridge, MA: Harvard University Press. 2Blough, D. S. (1963). Interresponse time as a function of continuous variables: A new method and some data. Journal of the Experimental Analysis of Behavior, 6, Hull, D. L., Langman, R. E. & Glenn, S. S. (2001). A general account of selection: Biology, immunology and behavior. Behavioral and Brain Sciences, 24,