Intro 1.

An Introduction to Developmental System Theory (DST)

A not uncommon reaction to DST is, ‘‘ That’s completely crazy, and besides, I already knew it.’’ - Susan Oyama, Evolution’s Eye, p 193.

Sydney Brenner, once proposed that in the future researchers would only need a sophisticated computer and a genome to compute most aspects of that individuals appearance and behavior. According to this commonly held view, the genome is a “code” or “blueprint” of all aspects of the organism, from its morphology, physiology, to its behavioral and cognitive traits. The environment simply provides the raw resources necessary for the unfolding of this latent genetic blueprint, and evolution consists of nothing more than changing allele frequencies in a population. But the idea that the genome is the central focus of biology is no longer tenable. Findings in animal behavior, epigenetics, developmental psychology, and genetics are causing once widely held assumptions about the nature of the genome, and its relationship to the organism and evolution, to be re-considered. 

In this first series of posts, I am going to be introducing developmental systems theory, and explaining the large implications that DST has for our understanding of evolution. I am assuming that most of my readers have an elementary understanding of evolutionary theory and population genetics and will understand words like, “selection”, “replicator”, “drift”, and “fitness”. If not, there are many wonderful resources on evolutionary theory that will be linked below. Many scholars know DST for its criticisms of the nature-nurture dichotomy and genetic determinism. But DST is more than this; it offers a alternative view of causation in biology and a comprehensive, non-reductionist view of organisms and their behavior. Introducing DST is not easy. A good way to break it down is to first focus on the three words that compromise DST.

Developmental:

Development describes change over time. All organism change over time, but developmental questions often address transitions individuals make across their lifespan, such as moving from crawling to walking in an infant. Not all changes that an organism undergoes fall under the domain of development, often such changes usually have to be irreversible changes in the organization of that system (see below). Development is also blind, meaning that there is no goal or pinnacle of development. Developmental processes depend on earlier conditions, but there is no overarching direction in this process. Questions such as, ‘how does language develop’ seek to identify the early conditions that are necessary and sufficient for language to emerge, even if these do not intuitively reflect our preconceptions of how language is acquired. Individual development is also a continual process that begins at conception and ends with death. It does not stop in adulthood.

Systems:

The word system describes a set of connected components that interact to form a cohesive whole. All organisms are systems, and depend on a diverse array of components in order to sustain themselves over time. A particularly important aspect of organismic systems is the interaction between the organisms and their environment. Survival is dependent on the continual interaction between internal components (endocrine components, physiological components, neural and genetic components) with external components (food, social interactions, mates, stimulation, temperature). Since all organisms exhibit changes over time, and such changes reflect the changing relationships between internal and external components, it is said that a defining aspect of organisms is that they are developmental systems.

Theory:

DST is a theory of how development occurs, and the implications of development for evolutionary processes. The word ‘theory’ is often contentious both among philosophers of science, and researchers themselves. Some see theories as ideas about the world that lead to testable experimental predictions, whereas others see theories as general patterns that reflect an accumulation of empirical findings pointing in a single direction. Often they are a mix of both, but DST tends to follow the latter. DST is often presented as a collection of perspectives drawn from empirical findings in developmental biology, animal behavior, developmental psychology and complex systems. The controversy around the word “theory” in DST has even led some researchers to propose replacing it with the word “thought”. One aim of this blog is to show that DST is not just a mere “collection” of ideas, but is a more of cohesive perspective. In particular, I hope to show how DST’s conception of an organism as a decentralized developmental system—wherein a wide array of interacting components shape developmental processes—can lead to testable empirical predictions regarding the development and evolution of behavior.

Suggested introductory papers on DST:

Griffiths, Paul E., and Russell D. Gray. "Developmental systems and evolutionary explanation." The Journal of Philosophy 91.6 (1994): 277-304.

Gottlieb, Gilbert. "Probabilistic epigenesis." Developmental science 10.1 (2007): 1-11.

Lehrman, Daniel S. "A critique of Konrad Lorenz's theory of instinctive behavior." The Quarterly Review of Biology 28.4 (1953): 337-363.

West, Meredith J., and Andrew P. King. "Settling nature and nurture into an ontogenetic niche." Developmental psychobiology 20.5 (1987): 549-562.

Suggested introductory papers on standard evolutionary theory:

Wright, Sewall. "Evolution in Mendelian populations." Genetics16.2 (1931): 97-159.

Mayr, Ernst. "Behavior Programs and Evolutionary Strategies: Natural selection sometimes favors a genetically" closed" behavior program, sometimes an" open" one." American scientist 62.6 (1974): 650-659.

Haldane, John Burdon Sanderson. "A mathematical theory of natural and artificial selection, part V: selection and mutation." Mathematical Proceedings of the Cambridge Philosophical Society. Vol. 23. No. 7. Cambridge University Press, 1927