Jan 24: Development--nature vs. nurture
“Nature vs. Nurture”
Just how do genes and environment interact?
• Radical behaviorism (Watson, Skinner): Most complex
behavior is entirely shaped by environment, and only loosely
constrained by genetics
• Classical ethology (Lorenz): Genes and environment make
distinct contributions, so behavioral capacities are either innate
or learned (and many complex behavior patterns are largely
innate)
• Modern view: Genes and environment interact in development
of all behavioral traits
Jan 15: Behavioral development: two forms
Two forms of behavioral plasticity in which to explore
the nature/nurture debate
Behavioral development
• Changes in behavior through ontogeny, as adult behavioral repertoire
develops
Learning
• Adaptive behavioral flexibility at a particular life stage
Alcock treats these as two different manifestation of a general
phenomenon: the flexibility of behavior in adapting the
individual to specific environmental conditions
Jan 15: Development--Filial imprinting intro
Case Study 1: Filial Imprinting
• Basic function: recognition of parents in
animals with precocial young (e.g., geese,
ducks)
• Dependence of recognition on experience
(“Nurture”)
¢
¢
Young animal must see model to recognize it
Learning is flexible: model may look unlike
own parent or even own species
• Genetic constraints on development of
recognition (“Nature”)
¢ Sensitive period of exposure to model
¢ Learning triggered by specific stimuli (e.g.,
movement, sound)
¢ Learning is rapid and long lasting
¢ Learning is apparently irreversible
Jan 15: Development--Filial imprinting cont’d
Imprinting-cont’d
• Sensitive period: learning is
strongest when chick is exposed
to model during particular time
window (for ducks, 10-20 hours
after hatching)
Height of curves indicates
strength of response to model
• Following of model (and learning)
triggered by sight and sound, but
sound is more potent than sight
Duckling
Hidden loudspeaker
Jan 15: Development--song learning intro
Case Study 2: Song learning in true songbirds*
• Functions of song (to be discussed in detail later in
course)
• Territorial defense (usually by males)
• Attraction of mates
• Song development
• Songs of true song-birds are usually species-specific, but their
development is influenced by experience
• Other bird groups that exhibit vocal learning: hummingbirds, parrots,
lyrebirds
• Most other bird species do not need experience to develop normal
vocalizations
* See Chap. 2 in Alcock
Jan 15: Development--song dialects
Song learning-cont’d
Dependence of song learning on experience (“nurture”)
• Flexibility in development of species
specific song: learned “dialects”
White-crowned sparrow
Dialect 1
Dialect 2
Jan 15: Development--song isolation exps
Song learning-cont’d
Dependence of song learning on experience (“nurture”)
• Flexibility in development of species
specific song: learned “dialects”
• Isolation experiments--isolated or
deafened birds develop degraded
song
Normal
Isolated
Deafened
Jan 15: Development--genetic constraints on song
Song learning-cont’d Genetic constraints on development (“Nature”)
• Sensitive periods: isolated
white-crowned sparrows must
hear species-specific song
between days 10 and 50 after
hatching
• Isolated birds can only learn
their own species’ song
Song sparrow
White-crowned
sparrow
Jan 15: Development: song template hypothesis
Song learning: the template hypothesis (P. Marler)*
• Brain encodes a “template” of species-specific song
• Template is used for recording correct song in memory
• Open only during senstitive period
• Selective for species-specific song (but any variant will do)
• Memorized song is used as basis for comparison during
practice phase
*The hypothesis that dominated ideas about song learning during 70s and 80s
Jan 15: Development: social cues
Role of social cues in song-learning: challenging the
dogma of the template hypothesis
• White-crowned sparrows may
change songs throughout lives
(i.e., well after critical period)
• Also, young birds given more
normal social experience (can see
as well as hear other birds
singing) have more flexibility in
their vocal development
• Thus, original template
hypothesis pertains only to
socially isolated birds
White-crowned sparrows given
social cues can even learn the
song of a different species!
Jan 15: Development: social cues
Beyond the template hypothesis
Jan 15: Development: other songbirds
Vocal development in other songbird species
• Some species learn a completely new song repertoire each year (e.g.,
canaries)
• Some birds add continually to song repertoire throughout their lives by
imitating songs of other species (e.g., mockingbirds, lyrebirds)
• Some birds mimic environmental sounds other than bird songs (e.g.,
parrots, starlings)
• In spite of this flexibility, there are still constraints on what can be
learned and under what circumstances it can be learned
Jan 15: Development: other songbirds
Why do species vary in level of vocal flexibility?
• This is a functional question (e.g., what is survival value of
vocal flexibility, and why don’t all birds have same need for
it?)
• Some hypotheses:
•Advantages of sharing local dialect (favors learning)
•Advantages of expanding repertoire size (favors learning)
•Costs of having to learn (disfavors learning)
Jan 15: Development: speedy mice
Inbred mice and speed
“Genetic” responses to amphetamine in two inbred mice strains
Cabib et al. 2000 Abolition and reversal of strain differences in behavioral
responses to drugs of abuse after a brief experience. Science 289:463.
Jan 15: hungry/speedy mice
Food deprivation alters strain-specific response
...then test again
Make mice hungry...