12.1 Essential ideas

12.1.4a Innate and learned behaviour 1 (HL)

  • Behaviours are conscious or unconscious actions that occur in response to external stimuli.

Fig 12.1.4a-a Stimulus - Response

Figure 12.1.4a/a – Stimulus-response pathway

  • Behaviour is coordinated by the central nervous system (CNS).

Innate behaviour is genetically determined and develops independently of the environment

  • Innate behaviour is:
    • Heritable – encoded in DNA and passed from generation to generation
    • Intrinsic – present in animals raised in isolation from others
    • Stereotyped– performed in the same way each time by each individual of a species
    • Inflexible – not modified by development or experience
    • Consummate – fully developed or expressed at first performance
    • Innate behaviours may be expressed at different stages of life. Examples include the suckling reflex in mammals and courtship behaviour in fruitflies. 

Figure 12.1.4a/b – Courtship behaviour in Drosophila meets the criteria for innate behaviour.Figure 12.1.4a/b – Courtship behaviour in Drosophila meets the criteria for innate behaviour.
Innate behaviours are displayed in the same stereotyped sequence or events each time the are performed.

A reflex is an autonomic and involuntary response

  • Reflexes are rapid unconscious responses to external stimuli. They are coordinated by the autonomic nervous system.
  • The pupil reflex and the patellar reflex are two examples. The stimulus-response pathways for these reflexes are summarised in the table below:


Pupil reflex

Patellar reflex (knee jerk)


Bright light shone in the eye

Tendon under the knee struck by object



Touch receptors in skin

CNS coordinator


Spinal cord


Muscles of the iris

Muscles of the quadriceps


Pupils close

Leg extends

A reflex arc is made of neurons that mediate reflexes

A reflex arc is the sequence of neurons that synapse with each other during a reflex response. A typical reflex arc consists of:

  1. Sensory neuron – An external stimulus initiates depolarisation in a sensory neuron. The impulse travels towards the central nervous system and synapses with a relay neuron.
  2. Relay neuron – These are part of the central nervous system. Relay neurons, or interneurons, connect neurons to each other, and are found in grey matter of the brain and spinal cord.
  3. Motor neuron – The relay neuron synapses with a motor neuron. Depolarisation in the motor neuron results in the response at the effector (muscle).

Application: Withdrawal reflex of the hand

  • The withdrawal reflex allows you to remove your hand from a painful stimulus (e.g. hot burner) before you are aware of the pain.
  • This is an important behavioural response that helps to minimise injury.

Skill: Diagram of a reflex arc for the withdrawal reflex

Figure 12.1.4a/c - Withdrawal reflexFigure 12.1.4a/c - Withdrawal reflex

  • Practise drawing the reflex arc shown in Figure 12.1.4a/c.

Learned behaviour develops as a result of experience

  • Learned behaviour is adaptable – it develops over time through experience.
  • There is individual variation in the performance of learned behaviour.
  • Learning involves the formation of new neural pathways – learning alters the phenotype but not the genotype, and therefore is not heritable.

Learning is the acquisition of a new skill or knowledge

  • The capacity for learning differs among species.
  • Social animals, animals with high parental involvement, animals with longer lifespans and more highly developed forebrains, are more likely to learn, especially from each other.


Figure 12.1.4a/d – Innate behaviours
Innate behaviours do not need to be learned and are often necessary for survival.

Essential idea

Behavioural patterns can be inherited or learned.

Key questions

  • Distinguish between innate and learned behaviour.
  • Draw a diagram of a reflex arc for the withdrawal reflex.
  • Outline the processes involved in a reflex response.

Figure 12.1.4a/e – Dolphins using ultrasound
Language skills are learned through experience. Cetaceans, such as dolphins and whales, communicate through learned ultrasound ‘languages’ that vary between social groups.

Concept help

  • External stimuli are perceived by sensors – see 12.1.3. The effector in a stimulus-response pathway is either a muscle or a gland.
  • Sensory neurons transmit impulses to the central nervous system (brain and spinal cord).
  • Motor neurons transmit impulses from the central nervous system.
  • Not all somatic reflexes require an interneuron. For example, the patellar reflex arc consists of a sensory neuron and a motor neuron.


It is easy for us to guess how the behaviour of an animal might influence its chance of survival and reproduction. Is intuition a valid starting point for scientific hypotheses?