Table of Contents
What Makes Behavior “Learned”?
Many behaviors are not fixed at birth but change through experience. Learned behavior is any relatively lasting change in an animal’s behavior that results from experience, not from simple maturation or one‑time fatigue or injury.
Key features of learned behavior:
- It depends on experience with the environment or other individuals.
- It can increase the animal’s success in finding food, avoiding predators, attracting mates, or caring for offspring.
- It often shows flexibility: the same individual can behave differently in different situations.
- It requires a nervous system that can store and modify information (memory and neural plasticity).
Learned and innate components are usually intertwined. Few behaviors are “purely” learned or “purely” innate; most are shaped by both genetic predisposition and experience.
Forms of Learning
Habituation
Habituation is the simplest form of learning: an animal’s response to a repeated, harmless stimulus becomes weaker over time.
- The stimulus is initially detected and elicits a response.
- With repeated exposure, if the stimulus has no important positive or negative consequences, the response declines.
- It is stimulus‑specific: the animal may still react strongly to a different stimulus.
Examples:
- A snail initially withdraws into its shell when touched, but after many harmless touches, withdraws less or not at all.
- Urban birds may stop flying away from passing pedestrians but still flee from a predator.
Biological significance:
- Habituation prevents wasting energy and attention on irrelevant stimuli, freeing the animal to focus on more important signals.
Sensitization
Sensitization is roughly the opposite of habituation: after a strong or noxious stimulus, an animal shows an increased response to later stimuli, even weak or different ones.
- Often follows pain, strong shock, or serious disturbance.
- The nervous system becomes “more excitable” for a time.
- Responses may be exaggerated compared with before.
Example:
- After a painful encounter with a predator, a prey animal may react more strongly to any sudden sound or movement.
Biological significance:
- Sensitization increases vigilance and defensive responses in dangerous situations, improving chances of survival.
Associative Learning
In associative learning, an animal learns the relationship between two events or between its behavior and its consequences. Two classic forms are:
Classical (Pavlovian) Conditioning
The animal learns that a previously neutral stimulus predicts a biologically important event.
Basic scheme:
- An unconditioned stimulus (US) naturally elicits an unconditioned response (UR) (e.g., food → salivation).
- A neutral stimulus (NS) (e.g., a sound) is repeatedly presented just before the US.
- The NS becomes a conditioned stimulus (CS), now able to elicit a conditioned response (CR) similar to the UR (sound → salivation).
Conditions for effective classical conditioning:
- Timing: The CS usually must reliably precede the US by a short interval.
- Contingency: The CS must predict the US better than other background cues.
- Relevance: Some CS–US combinations are learned more easily (e.g., taste → nausea).
Biological roles:
- Anticipation of important events (food, danger, pain).
- Formation of taste aversions: animals quickly learn to avoid foods associated with illness.
- Recognition of cues for predators, mates, or shelter.
Operant (Instrumental) Conditioning
Here the animal learns the association between its own behavior and the consequences of that behavior.
Basic principle:
- Behavior followed by a rewarding consequence (reinforcement) becomes more likely.
- Behavior followed by an unpleasant consequence (punishment) becomes less likely.
Key terms:
- Positive reinforcement: adding something pleasant (e.g., food reward) after a behavior.
- Negative reinforcement: removing something unpleasant (e.g., stopping a mild shock) when the behavior occurs.
- Punishment: adding something unpleasant or removing something pleasant to reduce the behavior.
- Extinction: if a behavior no longer leads to reinforcement, its frequency usually declines.
Examples:
- A rat presses a lever to receive food; lever‑pressing frequency increases.
- A dog sits on command to receive a treat.
- A predator improves its hunting technique because successful attacks are “rewarded” with food.
Schedules of reinforcement (how often a behavior is rewarded) strongly affect how stable the learned behavior is. Behaviors reinforced irregularly often persist longer when rewards stop than those reinforced every time.
Imprinting
Imprinting is a special kind of learning that occurs only during a limited “sensitive period” in early life and is usually long‑lasting and hard to reverse.
Main characteristics:
- Time‑limited: can only take place during a particular developmental phase.
- Often fast: sometimes a single exposure is enough.
- Specific target: the animal learns to recognize particular objects, individuals, or environments.
- Relative irreversibility: once established, the pattern is stable.
Forms of imprinting:
- Filial imprinting: young animals learn the characteristics of their parents or the beings they follow as “parents” (e.g., young geese following the first moving object they see).
- Sexual imprinting: young animals learn features of conspecifics that later influence mate choice.
- Habitat imprinting: young salmon, for example, imprint on the chemical signature of their natal stream, which helps guide their return as adults.
Biological significance:
- Ensures that young follow appropriate adults for protection and learning.
- Supports species‑specific mate choice and reproductive isolation.
- Helps animals orient and return to suitable habitats.
Insight and Problem Solving
Some animals, especially among birds and mammals with large, complex brains, can solve new problems in ways that do not rely on simple trial‑and‑error or direct conditioning sequences.
Insight learning and complex problem solving involve:
- Representing aspects of a problem mentally.
- Combining prior experiences in new ways.
- Suddenly arriving at a solution, sometimes after a pause with no visible attempts (“aha” effect).
Examples:
- Corvids (crows, ravens) using tools or combining objects (e.g., bending a wire into a hook to retrieve food).
- Primates stacking boxes to reach food or using sticks in novel ways.
These abilities depend on advanced neural processing and are often associated with long life span, social complexity, and flexible ecological niches.
Learning, Memory, and Neural Plasticity
Learned behavior requires that experiences leave lasting traces in the nervous system.
At the cellular and network level:
- Synaptic strength can increase or decrease depending on activity patterns.
- New synapses can form; existing synapses can be removed.
- Patterns of connectivity can change, forming “neural representations” of experiences.
Distinctions often made in memory research:
- Short‑term vs. long‑term memory: short‑term storage of information can, with repetition or importance, be consolidated into longer‑term changes in the brain.
- Procedural memory: learning of skills and habits (e.g., motor patterns in locomotion or song production).
- Declarative‑like memory: in some animals, memory for specific events or spatial locations (e.g., food caches in birds).
The details of the molecular mechanisms and brain structures involved differ among animal groups and are addressed elsewhere; here the key point is that behavioral learning relies on the ability of the nervous system to change with experience.
Constraints and Costs of Learning
Learning is not always beneficial. It has limits and costs.
Constraints:
- Genetic predispositions: animals are “prepared” to learn some associations easily and others poorly or not at all (e.g., taste–illness vs. sound–illness).
- Sensitive periods: some types of learning (like imprinting or language‑like learning in humans) are most effective or only possible during specific development phases.
- Sensory and motor limitations: an animal can only learn from stimuli it can detect and responses it can perform.
Costs:
- Time: an inexperienced animal may make mistakes that reduce survival or reproduction.
- Energy: maintaining large brains and learning capacities is metabolically expensive.
- Complexity of control: too much flexibility can be disadvantageous when a fixed response would be faster and reliable.
As a result, species evolve different balances between innate and learned components, depending on their ecology and life history.
Interaction of Innate and Learned Behavior
In real animals, innate and learned behaviors blend:
- Innate predispositions often define what is learned, when, and how quickly.
- Example: a young bird may be innately driven to sing, but it learns the specific song pattern from adult conspecifics during a particular learning phase.
- Learning refines, adjusts, or combines innate patterns to match local conditions.
- Example: a predator may have innate hunting sequences but learns where prey are most common or which techniques work best in a given habitat.
This interaction allows animals to be both reliably adapted (through inherited patterns) and flexible (through learning) in a changing environment.