Adaptation
Psychology 3106
Introduction
Last class we looked at what you might
call the ‘historical pathways’ that a
behaviour or trait can take
Basically, how you get from one form to
another
You can also look at the adaptive value
(fitness consequence) of behaviour
As noted, these are related
Adaptation: A Definition
An adaptation is a heritable trait that:
Either spread because of Natural Selection
and has been maintained by selection to the
preesnt
Or
Is currently spreading relative to alternative
traits, due to Natural Selection
More Adaptation
Nice thing about this definition is that it
can help us figure out if something is
indeed an adaptation.
Does it increase fitness?? That is the
question
What are the costs and benefits?
Not all traits are adaptations
The conditions that the trait evolved in
may not exist
The trait may be a maladaptive side effect
of an adaptive trait
The trait is a maladaptive expression of
some adaptive trait
The trait may be an exaptation
Measuring Fitness
Sometimes we can get direct measures of
fitness :
Gamete production
Offspring survival
Rate of copulation
Fertilized egg production
Offspring production
Offspring independence
Measuring Fitness
Often we have to go to indirect measures
of fitness :
Improved locomotion
Improved access to food
Improved survival chances
Improved access to territories
Better territories
An Example: Mobbing in Gulls
When you get near a nesting colony of
gulls they get pretty angry….
Dive bombing
Swooping
Hitting!
A good guess is that this behaviour is an
adaptation for defense of their young
But, as good as it sounds, does mobbing
increase fitness?
Mobbing Gulls
OK, if mobbing is indeed an adaptation
then, the degree of success experienced
by mobbing gulls in protecting their eggs
should be proportional to the degree to
which predators are actually mobbed.
Kruuk (1964) tested this prediction.
Placed 10 hen eggs, every 10 m on a line
leading from outside to inside a colony
The ones outside the colony were more likely
to have been taken
Kruuuuuuuuuuuuuuuuk (1964)
Mobbing in Barn Swallows
Barn Swallows also mob.
Could be self defense
Could be mating advertisement
Could be an alternative to parental care
Shields (1984) placed a stuffed owl near a
colony of barn swallows, and took note of
who mobbed
Shields (1984)
The Comparative Method
Just as with looking at the history of some
trait, the question of whether a behaviour
is an adaptation or not can be (partially)
answered with the Comparative Method
We would expect that birds that are cliff
nesters would not mob, while those that
were ground nesters would
Regardless of relatedness
Convergent and Divergent
Evolution
This is in fact the
case
The common
ancestor of Gulls and
Barn Swallows was
ages ago!
Indeed, some colonial
mammals mob!
Optimality Models
When does it make sense to use a
particular strategy?
When does it make sense to evolve a
particular strategy?
Look at the costs and benefits, thugh the
use of optimality models
Basically looking at costs and benefits
Optimality Models
You might mob some
of the predators some
of the time…..
Top model looks only
at costs and benefits
Bottom model looks
at percentage of
cautious and daring
mobbers, they are
dependent on each
other!
Criticism of the Adaptationist
Approach
Biggest critic was Stephen J. Gould
The only palaeontologist ever to appear on
The Simpsons
Trait may be maladaptive now, but
adaptive then
The trail may be a maladaptive byproduct
of an previously adaptive (or presently
adaptive) trait
More Criticisms by that baseball
loving commie
Trait would never have occurred in the
past, but new wacky conditions make it
show up now
The trait is less than ‘perfect’ because it is
constrained by past evolutionary events
Take that Dinosaur man
An assumption of adaptationism is that
traits are adaptive, we then test the
prediction.
It has never been about perfection Steve, I
don’t know what you read
The point is not to be correct, but to be
testable and proved wrong. You should
have paid more attention in Philosophy of
Science class. Science is not Essentialist!
Conclusions
Don’t be a ‘rabid adaptationist’
Don’t fall for the naturalistic fallacy either!
Remember, its all about reproductive
success in the end, so we really need this
approach to test why something evolved.
This stuff is all intertwined with the stuff on
the historical pathways of evolution that
we talked about earlier