Evolution refers to the process of change in gene frequencies within populations over many generations. The major principle of evolution is reproductive fitness, which refers to the likelihood that an individual will produce offspring or that that individual’s offspring will produce offspring. Evolution provides an explanation for how a mechanism developed but also why it developed. Previously adaptive mechanisms may not be adaptive anymore in modern society.

Evolutionary developmental psychology refers to a field which looks at development of humans from an evolutionary perspective. It is useful to look at which cognitive operations underlie adaptive behaviour. Psychological mechanisms (e.g. cognitive psychology) may be the missing link between evolution and behaviour.

It is possible that domain-specific mechanisms designed by natural selection to deal with specific aspects of the physical or social environment (e.g. face recognition) evolved. However, evolution has also influenced domain-general mechanisms (e.g. executive functions). There are three types of constraints on learning:

1. Architectural constraints
   This refers to the ways in which the brain is organized at birth (e.g. neurons). This limits the type of and manner in which information can be processed. This, in turn, influences what is processed as development progresses (e.g. no processing of peer feedback at infancy yet).
2. Chronotopic constraints (i.e. maturational constraints)
   This refers to limitations on the developmental timing of events (e.g. some brain areas develop earlier than others). Brain areas may be sensitive to certain types of learning during a particular timeframe (e.g. language learning), putting constraints on learning but also enabling it.
3. Representational constraints
   This refers to hardwired representations in the brain (i.e. innate knowledge). This guides and constraints learning (e.g. basic knowledge of objects).

These constraints indicate that people are prepared by natural selection to process some information more readily than other. Evolved probabilistic cognitive mechanisms refer to information-processing mechanisms that have evolved to solve recurrent problems faced by ancestral populations but they are expressed in a probabilistic fashion in each individual in a generation. This means that it will develop in a species-typical manner if the individual experiences a species-typical environment but if not, development will be different (e.g. people are not innately afraid of snakes but are ready to develop a fear of snakes if the environment gives reason for this).

According to Geary, the mind is a set of hierarchically organized domain-specific modules that develop as children engage their physical and social worlds. Though people have domain-specific modules, human cognition is adaptive to local conditions. Development fine tunes the modules that are very flexible and broad.

The long period of youth in children may be necessary or children to master complexities of human societies and technologies. This means that cognition needs to be adapted to a wide range of environments. There are biologically primary abilities (e.g. language):

1. This has undergone selection pressure and has evolved to deal with problems faced by our ancestors.
2. This is acquired universally.
3. This is acquired by children in all but the most deprived environments.
4. Children tend to reach expert level of proficiency.
5. Children are intrinsically motivated to exercise these abilities and do so spontaneously.

There are also biologically secondary abilities (e.g. reading):

1. This does not have an evolutionary history but is based on biologically primary abilities.
2. This is culturally dependent (i.e. it reflects the cognitive skills important in a culture).
3. Children are not intrinsically motivated to learn this.
4. This may require tedious practice.

Neuroconstructivism states that evolved learning abilities interact with a structured, expected environment to produce species-typical patterns of cognitive growth.

Epigenesis states that individual development is characterized by an increase in novelty and complexity of organization over time. Genes are expressed as a result of the environment and the genes, in turn, influence the environment which influences gene expression. Experience has influence on the cellular level. As a result of epigenesis, it is necessary to take the relationship between the individual and the environment into account.

The developmental systems approach states that new structures and functions emerge during development as a result of self-organization through the bidirectional interactions of elements at various levels of organization (e.g. genes, environment). The relationship between genes and the environment is what leads to development and the interaction between these two is of prime interest.

Genes are expressed differently in different environments. However, people still develop in a species-typical way because there is also a species-typical environment. Both species-typical genes and species-typical environments contribute to species-typical development and behaviours seen as ‘instinctive’.

The timing of a particular event can influence what effect that event will have on development. The sensitive period (i.e. critical period) refers to the period in development when a particular skill (e.g. language) is most easily acquired. Both the presence and absence of experience can play a big role in a sensitive period (e.g. absence of fine-tuned perceptual system prevents sensory overload which leads to a better understanding of the world). A poor functioning in one sensory system might permit another sensory system to develop without undue competition for resources. This means that premature stimulation of a sensory system may be adverse for the development of that or another sensory system. Timing of exposure to events may be responsible for species-typical patterns of brain and cognitive development and this may be what is inherited (i.e. instinctive behaviour).

Behavioural genetics studies the genetic effects on behaviour and complex psychological characteristics (e.g. intelligence). The gene -> environment theory states that one’s genotype influences which environments one encounters and the type of experience one has. This means that genes drive experience (e.g. genetic make-up determines how one organizes the world).

A child’s phenotype is influenced by the genotype and the environment. A parent’s genotype influences the child’s genotype but also the environment (e.g. the parent’s genetic characteristics affect the type of environments they are most likely to encounter in life).

There are three types of genotype -> environment effects:

1. Passive effects
   This occurs when biological parents provide the rearing environment of the child. In this case, the effects of genetics and environment cannot be separated. These effects decline with age.
2. Evocative effects
   This occurs when the child elicits responses from others that are influenced by their genotype (e.g. the response a child receives when the child is irritable). These effects remain constant throughout development.
3. Active effects
   This occurs when one’s genotype influences the type of environment one chooses to experience (e.g. a person actively selecting an environment). These effects increase as children become older.

High-density event-related potentials are a form of EEG that permits detailed recoding of brain activity when people solve cognitive tasks or are presented with specific stimuli. PET and single-photon emission computed tomography (SPECT) use radioactive material to reflect brain activity.

Electrical and chemical signals are transmitted from a neuron. The axon is the projection away from the cell body of the neuron. This carries messages to other cell bodies. Dendrites receive messages from other cells and transfer them to the cell body. Between the dendrite and the axon, there is a synapse. Here, messages are transmitted by releasing neurotransmitters. The condition at the synapse affect the transmission of the messages among neurons.

Myelinated axons fire more rapidly (1), have lower thresholds of sensitivity to stimulation (2) and have greater functional specificity (3). The process of myelination increases throughout childhood and adolescence. This proceeds at different rates for different areas of the brain.

Neurons go through three stages of development:

1. Proliferation (i.e. neurogenesis)
   This is the process of production of new neurons through mitosis. This mostly occurs early in development during the prenatal period
2. Migration
   This is the process of moving the neurons to their permanent position in the brain and is mostly finished by approximately 7 months after conception.
3. Differentiation
   This is the process of growing in size (1), producing more dendrites (2), extending their axons (3) and creating synapses (4). Most of this process takes place after birth.

Faulty migration of neurons has been associated with disorders (e.g. epilepsy). Synaptogenesis is rapid during the early years of life. There are more synapses in a child’s brain compared to an adult brain. The number of synapses reduce as a result of experience pruning (i.e. selective cell death; apoptosis). Synaptogenesis and apoptosis occurs at different rates for different parts of the brain.

The process of rapid development followed by decline occurs in multiple areas of brain development (e.g. brain metabolism). Developmental changes in the presence of neurotransmitters also occurs.

The hypermetabolism of the brain may be necessary for the rapid learning of that time. The increase in the number of neurons and synapses compared to adults may also allow for more brain plasticity. However, the failure of selective pruning is associated with disorders (e.g. schizophrenia).

In children with a higher IQ, there is an acceleration of cortical growth and an accelerated thinning in adolescence.

There is a reciprocal relationship between brain and behavioural development. Specific experiences may produce neural activity which determines which of the excess synapses will remain. Experience-expectant processes (i.e. experience-expectant synaptogenesis) refers to the processes whereby synapses are formed and maintained when an organism has species-typical experiences. Experience or lack of experience changes the structure and organization of the young brain.

Experience-dependent processes (i.e. experience-dependent synaptogenesis) refers to processes in which connections among neurons are made after the unique experiences (i.e. non-species typical experience) of an individual rather than a species-typical experience.

The corpus callosum connects the two hemispheres of the brain. The prefrontal lobes may be important in inhibiting behavioural responses and could explain the A-not-B error. In adolescence, a mismatch in maturation may occur where the amygdala and limbic system reaches adult levels before the prefrontal cortex. This may partially explain adolescent behaviour. This behaviour may be adaptive in establishing independence of the parents.

Plasticity refers to the ability to change. There is barely any plasticity in the production of new neurons in the cerebral cortex. New synaptic connections can be formed throughout life. Synaptic plasticity is greatest in infancy. Losing plasticity can lead to neurons dedicating themselves to one goal. This leads to greater efficiency of processing.

The early plasticity view of brain damage states that brains of young children are highly plastic relative to adults. This means that these brains are better able to overcome the effects of brain damage. The Kennard effect states that a younger brain is more likely to recover normal function than an older brain. This effect does not hold for all types of brain damage. Very early brain damage (e.g. prenatal brain damage) often results in permanent neurological impairment.

Recovery depends on injury factors (1), age factors (2), environmental factors (3) and the type of rehabilitation (4). Recovery is often greater when a more general cognitive function is damaged (e.g. executive function). Extended immaturity of the human nervous system allows for resilience (1), behavioural flexibility (2) and plasticity (3). Young children have a slower and more inefficient processing speed and this allows for better adaptation to later environments.

Interactive specialization models of brain development states that cortical development is a self-organizing process. There is a bidirectional interaction between brain structure and psychological function.