MadSci Network: Neuroscience

Re: Do humans have instincts or just reflexs?

Date: Thu Sep 13 10:48:59 2001
Posted By: Louise Freeman, Professor
Area of science: Neuroscience
ID: 999827863.Ns

Dear Joe,

At the risk of sounding like a certain ex-president, it all depends on how 
you define the word "instinct."  This situation is complicated by the fact 
that people colloquially use the term "instinct" to refer to any sort of 
more or less automatic response...  "Carol instinctively cringed when her 
ex-boyfriend entered the room."  Behavioral scientists, however, mean 
something very different by instinct.  Because of this confusion, many 
modern textbooks are using a different term, "fixed action pattern" to 
refer to behaviors that used to be called insticts.  Reflexes and fixed 
action patterns do indeed refer to different types of behaviors.  I'll try 
to explain the difference.

A reflex is a simple and automatic response to a single stimulus.  They are 
not learned...  most appear at birth.  All animals, including humans, have 
reflexes.  The most popular example in humans is the stretch or kneejerk 
reflex...  the tap of a doctors hammer on the knee stretches a certain 
tendon. Sensory neurons from that tendon activate motor neurons on a 
particular muscle, and your leg jerks forward.  Other reflex responses in 
humans include blinking your eyes in response to dust on the cornea, 
salivating in response to the taste or smell of food and sneezing in 
response to an irritant in the nose.

Fixed action patterns are more complex than reflexes.  They are generally 
define as an inherited set of actions in response to a particular stimulus. 
For instance, a snake senses the heat of a mouse and first constricts, than 
swallows it.  A male stickleback fish sees the red underbelly of another 
male stickleback and attacks it in a stereotyped way.  The stimuli that 
trigger these behavioral patterns (called a releaser or a sign stimulus) is 
often very specific..  the fish will not attack another fish whose belly 
has been painted a different color, but will attack a similar-sized toy 
submarine if the underside is painted red.  The snake will starve to death 
if you try to feed it cold raw meat but may try to constrict and swallow a 
light bulb in its cage.  Often, once fixed action patterns are started, 
they must be completed.  For instance, if a goose kicks an egg out of her 
nest, the sight of the round object will prompt her to leave the nest, 
walk over to it and roll it back into her nest with her bill. Placing a 
tennis ball or other round object a similar distance away will prompt the 
same behavior.  However, if you remove the egg halfway through her trip 
back to the nest, she will continue back to the nest with her bill on the 
ground, "rolling" the now-absent egg.

The question is, then, are there fixed action patterns in humans?  
Surprisingly, scientists do not agree on this answer.  It's hard to 
visualize any human behavior that is that stereotyped, that automatic, that 
 is definately inheritied, not learned.  Some have argued that behaviors 
such as caring for babies or the incest taboo are fixed action patterns, 
but this is debatable.

I hope this answers your question.

Louise Freeman
Source: Paul Chance's _learning and Behavior_

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