In precocial species, the young are physically mobile and able from the moment of birth and in altricial species the young are helpless. Nativism is the view that many skills or abilities are native or hard-wired into the brain at birth. Empiricism is the view that humans are a blank slate at birth. Cognition is mental activity.

Binet introduced the term mental age, which can be defined as an individual’s level of mental ability relative to others. Chronological age is a person’s actual age. The intelligence quotient is a measure of a person’s level of intelligence compared to a population of individuals of approximately the same age. There are four important things to note about IQ tests and IQ scores:

1. The purpose of the IQ test is always to compare people’s scores with those from people of the same population and same age.
2. The average IQ at a given time is always 100. Tests are standardised to ensure this.
3. People’s IQ scores tend to increase from one generation to the next (Flynn effect).
4. The items on IQ tests invariably proceed from the simple to the complex, so that an individual’s raw score is derived from the number of items passed before making mistakes.

Some people argue that a general intelligence underlies the scores of an intelligence test and some people argue that intelligence is made up of several individual components. Many intelligence tests divide intelligence into verbal and performance subscales.

Heritability is a statistical measure that describes how much of the variation of a trait in a population is due to genetic differences rather than environmental differences in a population. Heritability estimates refer to a population and tell us nothing about individuals. Genetic determinism is the hypothesis that people become who they are as a consequence of their genetic inheritance. Environmentalism is the hypothesis that people become who they are as a consequence of the learning and experiences they have had throughout life.

The familial resemblance is the resemblance between relatives whose genetic relationship to each other is known. The familial resemblance is a type of evidence concerning genetic influences to cognitive development. Missing heritability refers to the failure to find any of the genes associated with cognitive abilities. A gene and environment interaction are when different genotypes respond to similar environmental factors in different ways to create an individual’s phenotype. There are several environmental factors that create different phenotypes, depending on the individual, because the genotype of the person differs. An example of this is phenylketonuria, a disease which can cause severe mental retardation, unless on a phenylketonuria free diet, which shows that the same environmental factor (diet) can have different phenotypes as an outcome (mental retardation or not).

Studies on adoptees have shown that an early deprived upbringing can have serious detrimental effects on children’s development and that these detrimental effects can be partially reversed by placement into good quality adoptive homes. Environmental drift refers to changes in developmental functions that result from, and are in the direction of changing environments.

The Flynn effect is an average increase in the average intelligence quotient test scores over generations. Raven’s Progressive Matrices is a culture-free non-verbal intelligence test with items arranged in order of difficulty.

Malnutrition can have a devastating effect on children’s development. Absolute poverty refers to limited access to food and/or clean water. Relative poverty is poverty in households which earn 60 percent or less than the median income. A highly stimulating and nurturant environment facilitates brain growth while a limited non-nurturant environment inhibits it.

Compensatory education offers supplementary programmes or services designed to help children at risk of cognitive impairment and low educational achievement. The longer a child lives in poverty, the greater their academic deficits.

Head Start is a project in the USA aimed at breaking the cycle of poverty of low-income children from birth to age 5. The positive effects of the project soon diminished after it had stopped for the children. Sure Start is the UK equivalent of Head Start. Whether the effects of the projects last depends on whether teachers and parents respond to the initial changes in the children’s behaviour and performance. Parental involvement in children’s education and development is an important factor.