Epigenesis

PSC 113Jeff Schank

Outline

• Innateness– Developmental Fixity– The Strategy of Backward Causal Inference and Its Problems

• Four Types of Questions (Tinbergen)– Mechanistic– Phylogenetic– Ontogenetic– Survival Value

• Epigenesis• Umwelt• Generative Entrenchment

Innateness• Innateness as developmental fixity is the view that psychological and

behavioral development in humans and other animals is fixed (especially early in development)

• Preformationism is the view that organisms develop from miniature versions of their adult form– Nicolaas Hartsoeker thought, in 1694, that he

could see tiny men inside of sperm when viewed threw a microscope

• Ideas are eternal and fixed in the mind Plato in the Meno argued for view that ideas are innate

• Closed program: behaviors early in development are determined by genetic programs– Genetic determinism

The Strategy of Backward Functional Inference and Its Problems

• From a functional perspective (in the evolutionary adaptive sense), one might focus on the adaptive consequences of behavior and look for the sequence of developmental events leading up to a behavior and conclude that experience is not involved

• Using backward functional inference, one infers that a behavior is innate if at an early stage of development the behavior has high adaptive value (e.g., pecking at a parent’s beak for food)

Infer that it is innate

Ontogenetic Perspective

• Does this imply that experience is not required for “innate” behaviors? –It does not!

• From an ontogenetic perspective, development is a causal process in which a myriad of environmental, genetic, historical, and social factors play a causal role at each stage of development

• From this perspective, backward functional inference is not a very good strategy of inference because it will miss factors that play a role in the development of a behavior

Laughing Gull Chicks

• Laughing gull chicks will approach and peck at a parent’s beak as a consequence of a croon call by a parent

• Parents then regurgitate food for the chick to eat • From an adaptive functional perspective, failure of

a chick to approach would be very maladaptive!• Therefore, based on backward functional

inference, the behavior of approach and pecking at a parent’s beak must be innate

Impekoven and Gold (1973)

• They showed that the ability of gull chicks to respond appropriately to the croon calls of their parents depends on the chicks having heard the calls before they are hatched!

• They found that– Parents when incubating the nest make croon calls

– Several days before the chicks hatch, they begin to peep, which stimulates the parents to croon even more

– Chicks raised in incubators do not have the typical approach response to croon calls, but instead crouch and hide

Tinbergen’s Four Questions• Tinbergen distinguished four such questions for the study of behavior

1. Mechanistic questions are about the mechanisms that cause behavior (e.g., crooning in laughing gull chicks, chemical signals given off by newly emerged works in army ant colonies, increased estrogen levels in ringdove females in response to male courtship behaviors)

• Mechanisms can be analyzed in terms of our four causes

• A mechanism has components that proximally interact to generate organized patterns of behavior

• For example, the mechanism of flocking consists of birds that align with their nearest neighbors, fly close to them, but avoid collisions, which generates flocking

• Mechanism also have function such as the synchronous twitching of fall webworms deters predatory wasps and flies

Four Questions continued…

Tinbergen’s Four Questions• Tinbergen next three questions…

2. Phylogenetic questions concern the evolutionary history of behaviors and their mechanisms (e.g., if fall webworms that twitch synchronously when flies or wasps land on their web have a slightly better chance of surviving, then how has the trait spread?).

3. Ontogenetic questions concern the development of individuals, focusing on causal conditions preceding each stage of development (e.g., how does croon calling in laughing gull chicks emerge during development?).

4. Survival Value questions concern the adaptive value of behaviors (i.e., survivability and fecundity of animals; e.g., finding a mate, selecting a mate, holding territories and resources, preferences for odors in amniotic fluid).

Epigenesis

• Is the view that development is

– (i) not predetermined or fixed,

– (ii) not reducible to genetic programs, but

– (iii) is a process involving interactions from many levels of organization acting on each stage of development

Life Cycle of a Tick

Umwelt of a Tick

Positive geotaxis Drops when it detects butyric acid

Moves towards fur (or hair) and warm bodies

Lewontin extends the Definition of Umwelt

• An animals Umwelt is its sensory-reactive world and an animal actively constructs it Umwelt by– Assembling: Organisms partially assemble their environments, e.g.,

many birds build nests, social insects build nests, spiders weaving webs.

– Altering: In interacting with their environments they alter them (e.g., masses of locusts devouring vegetative matter in their path or elephants pulling down trees to feed on the leafy branches)

– Transducing: The take in energy and perceive stimuli and produce physical products and behavioral interactions

– Modulating: They regulate their environments (e.g., fall webworms can by twitching modulate their environment and affect the Umwelt of a fly)

Early Stages of Development

Generative Entrenchment• Epigenesis is a generative process meaning that each stage development is

causally generated from previous stages and the environment

• William Wimsatt first noticed changes early in development (e.g., genetic mutations, changes in the environment), have more effects on development than changes later in development, because early changes can causally cascade through development

• if most arbitrary or random changes in development are deleterious to the adaptive function of the developing organism at any later stage of development, then ceteris paribus early stages of development will tend to be more stable and the interactions with the environment will be more stable

• This explains von Baer’s Law (he argued that Ernst Haeckel’s view that “ontogeny recapitulates phylogeny” is not factually correct; embryos tend to be more similar early in development and diverge later)

A Model of Generative Entrenchment

Early Change

Late Change

Innateness Again• If we mean by innate behavior, behavior that emerges early and is

critical for later development, then the more generatively entrenched a behavior is, the more innate it is

• Notice that innateness is no longer tied to genes but rather to factors early in development (i.e., genes, environmental factors, anatomical or physiological structures or processes) that play a generative role in development

• Innate factors will tend to occur early in development and are resistant to evolutionary change

• Laughing gull chicks’ approach to croon calling parents is innate on this view because even though experience is required, experience is entrenched early in development