Summary
The term instinct is commonly thought of as describing behavior that is
pre-programmed and requires no thought. An instinctive response happens
automatically and is the same across all individuals of a species. While this
seems like a clearly defined category, not all behavior is so cut and dry. Many
behaviors have both genetically pre-programmed and learned aspects. The degree
to which certain behaviors, especially in humans, are pre-determined is often a
subject of intense debate.
When looking at instinctive behaviors, we must first understand the terminology
used to describe such behaviors, and then we must consider some of the concerns
involved in studying them. Any thing or event that triggers a behavior is called
a key stimulus (KS). Key stimuli produce fixed action patterns (FAP)
through innate releasing mechanisms (IRM). Several KS may be needed
to
trigger an FAP and different degrees of a KS can result in different strength
FAP response. Different classes of sensory receptor cells are important in the
receiving of different types of KS. The associated neural networks of these
different sensory cells help to integrate the signal from many receptors to
determine the degree of the KS and thereby produce an appropriate level of
response. Many of these responses are determined by carefully regulated internal
messenger molecules called hormones. The endocrine system, which is
responsible for the production and transport of hormones throughout the body, is
made up of many secretory glands that produce hormones and release them for
transport to target organs. In vertebrates, neural control of this system is
funneled through the hypothalamus to the anterior and posterior pituitary gland.
Whether the behavioral response to a given KS is learned, genetic, or both is
the subject of study in the field of behavioral genetics. Researchers use
techniques such as inbreeding and knockout studies to attempt to separate
learning and environment from genetic determination of behavioral traits.
