Where Does Intelligence Come From:
Belief that everything we know and think is a product of our experience with the world.
Leibniz’s view: they think human beings as the joint product of nature and nurture, where
they gain characteristics that are endowed and of the experiences.
Genetic Influences of Intelligence:
Members of the same family may have similar levels of intelligence because they share
the same genes and environment-or both.
When siblings have the same biological parents but different birthdays, they share the
50% of their genes
Fraternal twins: twins who develop from two different eggs that are fertilized by two
different sperm-they share average of 50% of the genes.
Identical twins: twins who develop from splitting of a single egg that was fertilized by a
single sperm and they share 100% of their genes.
Identical twin test scores are strongly correlated when brought up in the same household.
But there is also a correlation if they are not brought up in the same house.
People who share all their genes have similar intelligence test sores regardless of whether
they share their environment.
Genes play an important role in determining intelligence
Heritability coefficient: is a statistic that describes the proportion of the difference
between people’s scores that can be explained by differences in their genes.
50 percent of the difference between people’s intelligence test scores is due to genetic
differences between them (that doesn’t mean 50 percent genes, 50 percent environment)
The intelligences of a single person is a product of both genes and experiences and
cannot be “due” to one of these things more than the other.
This coefficient, tell us why people in a particular group differ from one another.
People with identical experience, then differ due to genes, and when people have
identical genes they differ in experiences.
Shared environment: those environmental factors that are experienced by all relevant
members of a household.
Correlation between IQ scores of siblings decrease as the age difference between them
increases due to different shared environments.
The family environment does not matter for development, but what matters is the
individual environment of these children.
Environmental Influences on Intelligence
Traits that are strongly influenced by genes may also be strongly influenced by the
Relative intelligence: generally stable over time (if your intelligent at age 11 , you will be
at age 80)
Absolute intelligence: change considerably over time. Intelligence tends to increase
between adolescence and middle age and then decline after Absolute intelligence tends to decrease across the average life span, but increase through
Flynn effect: average intelligence test score has been