Lecture 1 Genes and evolution
What is psychology?
Psychology is the scientific study of the mind, brain, and behavior (Phelps et al., 2022).
But why do we need science to study human behavior if we already have common sense?
Because common sense can be wrong. We often think we know why people behave in a
certain way, but our assumptions are not always supported by evidence. Psychology uses
scientific research to understand how people think, feel, and behave.
The genetic basis
Is it correct to say that “a violent person has violent genes”?
The answer has changed over time:
● In the 1970s: researchers mainly focused on the environment. The idea was that
violent behavior was learned from a violent environment. For example, growing up
around violence could increase the chance of becoming violent.
● In the 1990s: researchers increasingly focused on genes. They started to recognize
that genetic differences could also influence behavior.
● Today: we understand that it is not simply genes OR environment. Instead, genes
and environment interact with each other and together influence behavior.
So, it is too simple to say that someone is violent because they have “violent genes.” Genes
can influence how someone develops, but environmental experiences can also influence
how those genes work.
The genetic basis (Genes)
Genes are meaningful sections of a molecule called DNA.
DNA is the biological material that contains the instructions needed to build and maintain an
organism. You can think of DNA as a very large instruction manual, and genes are specific
sections of that manual.
Genes provide instructions for making proteins. Proteins are molecules that perform many
important functions in our cells, such as helping cells grow, communicate, and function
properly.
Therefore:
DNA → contains genes → genes contain instructions → instructions help make proteins →
proteins help cells function
Gene expression
,Gene expression means whether a gene is being used (“turned on”) or not being used
(“turned off”).
A gene does not have to be active all the time. Different cells need different proteins, so
different genes are active in different cells and at different moments.
For example, a gene that is needed in a brain cell may be active in that cell, while the same
gene may be inactive in another type of cell.
Gene expression is influenced by the biochemical environment inside the cell. This
environment can be influenced by:
● the environment outside the cell
● the timing of development
● the person's overall environment
● experiences
● behavior
One way gene expression can be changed is through methylation.
Methylation happens when a small chemical group called a methyl group is added to a
section of DNA.
Methylation does not remove or destroy the gene. Instead, it can make the gene less
accessible, which often means that the gene becomes less active and produces less of its
product.
So, an important idea is:
Having a gene does not necessarily mean that the gene is active.
The environment and experiences of an organism can influence which genes are expressed.
This is one reason why genes and environment cannot always be separated when
explaining behavior.
Genome
The genome is the complete set of DNA in an organism. In simple terms, the genome is
the organism's entire collection of genetic information.
So → all of the organism's DNA
Genotype
A genotype is the specific set of genes that an individual organism has.
In other words, your genotype refers to your particular genetic makeup.
For example, two people can have different genotypes because they have different versions
of certain genes.
,Phenotype
The phenotype refers to the traits and behaviors that we can observe in an organism.
This can include physical characteristics, such as height or eye color, but also certain
aspects of behavior.
The phenotype is influenced by both genotype and environment:
Phenotype = genotype × environment
The environment here includes both past and present experiences.
This means that our characteristics and behavior are not determined by genes alone. Our
genes interact with our experiences and environment.
A good example is monozygotic (identical) twins.
Identical twins come from the same fertilized egg and therefore have very similar genetic
information. They have a very similar genotype. However, they can still grow up having
different experiences and environments. As a result, identical twins can develop differences
in their characteristics and behavior.
Each gene is paired with another gene. The pairs are located at corresponding positions on
pairs of chromosomes. Alleleis one specific variant of a gene. dominant. recessive.
To understand this, we first need to understand chromosomes.
A chromosome is a structure made of DNA. Chromosomes organize and store our genetic
information.
Humans normally have pairs of chromosomes. You receive one chromosome of each pair
from your biological mother and one from your biological father.
Genes are located on chromosomes. A specific gene has a specific position on a
chromosome. This position is called a locus (plural: loci).
Because chromosomes come in pairs, you usually have two copies of a particular gene: one
inherited from each biological parent.
The two copies can be the same or different. Different versions of the same gene are called
alleles.
For example, imagine a gene that exists in two different versions:
Allele A + Allele A or Allele A + Allele B
The alleles you have can influence certain traits. Some alleles are described as dominant,
while others are described as recessive. A dominant allele can influence the phenotype
when only one copy is present. A recessive allele generally influences the phenotype only
when the individual has two copies of that recessive allele.
, It is important to remember that dominant does not mean “better” or “stronger.” It only
describes how an allele is expressed in relation to another allele.
Homozygote
An organism is homozygous when the two alleles at a particular locus are the same.
Heterozygote
An organism is heterozygous when the two alleles at a particular locus are different.
A specific trait or behavior is determined by the interaction between the environment (past
and present) and a specific trait or behavior can be influenced by the interaction between
genes and the environment.
Sometimes, a trait can be influenced mainly by one pair of genes. However, many traits
and behaviors are much more complicated and are influenced by many different gene
pairs. This is called polygenic inheritance.
Polygenic inheritance means that a characteristic is influenced by multiple genes rather
than by one single gene. Therefore, when studying behavior, we should generally not think:
“One gene → one behavior.”
Instead, behavior is usually the result of a much more complicated interaction between:
many genes + past experiences + present environment + other biological processes →
behavior
Evolution by natural selection
Where do our parents' sets of genes come from?
Our parents inherited their genes from their parents, who inherited their genes from their
parents, and so on.
This means that the genetic information we have today has been passed down through
many generations.
Over very long periods of time, the genome of a population can change through evolution.
This idea is strongly associated with Charles Darwin and his theory of evolution.
Charles Darwin proposed that all modern organisms are descended from earlier organisms.
In other words, different species share common ancestors and have changed over many
generations through the process of evolution.
Natural selection
What is psychology?
Psychology is the scientific study of the mind, brain, and behavior (Phelps et al., 2022).
But why do we need science to study human behavior if we already have common sense?
Because common sense can be wrong. We often think we know why people behave in a
certain way, but our assumptions are not always supported by evidence. Psychology uses
scientific research to understand how people think, feel, and behave.
The genetic basis
Is it correct to say that “a violent person has violent genes”?
The answer has changed over time:
● In the 1970s: researchers mainly focused on the environment. The idea was that
violent behavior was learned from a violent environment. For example, growing up
around violence could increase the chance of becoming violent.
● In the 1990s: researchers increasingly focused on genes. They started to recognize
that genetic differences could also influence behavior.
● Today: we understand that it is not simply genes OR environment. Instead, genes
and environment interact with each other and together influence behavior.
So, it is too simple to say that someone is violent because they have “violent genes.” Genes
can influence how someone develops, but environmental experiences can also influence
how those genes work.
The genetic basis (Genes)
Genes are meaningful sections of a molecule called DNA.
DNA is the biological material that contains the instructions needed to build and maintain an
organism. You can think of DNA as a very large instruction manual, and genes are specific
sections of that manual.
Genes provide instructions for making proteins. Proteins are molecules that perform many
important functions in our cells, such as helping cells grow, communicate, and function
properly.
Therefore:
DNA → contains genes → genes contain instructions → instructions help make proteins →
proteins help cells function
Gene expression
,Gene expression means whether a gene is being used (“turned on”) or not being used
(“turned off”).
A gene does not have to be active all the time. Different cells need different proteins, so
different genes are active in different cells and at different moments.
For example, a gene that is needed in a brain cell may be active in that cell, while the same
gene may be inactive in another type of cell.
Gene expression is influenced by the biochemical environment inside the cell. This
environment can be influenced by:
● the environment outside the cell
● the timing of development
● the person's overall environment
● experiences
● behavior
One way gene expression can be changed is through methylation.
Methylation happens when a small chemical group called a methyl group is added to a
section of DNA.
Methylation does not remove or destroy the gene. Instead, it can make the gene less
accessible, which often means that the gene becomes less active and produces less of its
product.
So, an important idea is:
Having a gene does not necessarily mean that the gene is active.
The environment and experiences of an organism can influence which genes are expressed.
This is one reason why genes and environment cannot always be separated when
explaining behavior.
Genome
The genome is the complete set of DNA in an organism. In simple terms, the genome is
the organism's entire collection of genetic information.
So → all of the organism's DNA
Genotype
A genotype is the specific set of genes that an individual organism has.
In other words, your genotype refers to your particular genetic makeup.
For example, two people can have different genotypes because they have different versions
of certain genes.
,Phenotype
The phenotype refers to the traits and behaviors that we can observe in an organism.
This can include physical characteristics, such as height or eye color, but also certain
aspects of behavior.
The phenotype is influenced by both genotype and environment:
Phenotype = genotype × environment
The environment here includes both past and present experiences.
This means that our characteristics and behavior are not determined by genes alone. Our
genes interact with our experiences and environment.
A good example is monozygotic (identical) twins.
Identical twins come from the same fertilized egg and therefore have very similar genetic
information. They have a very similar genotype. However, they can still grow up having
different experiences and environments. As a result, identical twins can develop differences
in their characteristics and behavior.
Each gene is paired with another gene. The pairs are located at corresponding positions on
pairs of chromosomes. Alleleis one specific variant of a gene. dominant. recessive.
To understand this, we first need to understand chromosomes.
A chromosome is a structure made of DNA. Chromosomes organize and store our genetic
information.
Humans normally have pairs of chromosomes. You receive one chromosome of each pair
from your biological mother and one from your biological father.
Genes are located on chromosomes. A specific gene has a specific position on a
chromosome. This position is called a locus (plural: loci).
Because chromosomes come in pairs, you usually have two copies of a particular gene: one
inherited from each biological parent.
The two copies can be the same or different. Different versions of the same gene are called
alleles.
For example, imagine a gene that exists in two different versions:
Allele A + Allele A or Allele A + Allele B
The alleles you have can influence certain traits. Some alleles are described as dominant,
while others are described as recessive. A dominant allele can influence the phenotype
when only one copy is present. A recessive allele generally influences the phenotype only
when the individual has two copies of that recessive allele.
, It is important to remember that dominant does not mean “better” or “stronger.” It only
describes how an allele is expressed in relation to another allele.
Homozygote
An organism is homozygous when the two alleles at a particular locus are the same.
Heterozygote
An organism is heterozygous when the two alleles at a particular locus are different.
A specific trait or behavior is determined by the interaction between the environment (past
and present) and a specific trait or behavior can be influenced by the interaction between
genes and the environment.
Sometimes, a trait can be influenced mainly by one pair of genes. However, many traits
and behaviors are much more complicated and are influenced by many different gene
pairs. This is called polygenic inheritance.
Polygenic inheritance means that a characteristic is influenced by multiple genes rather
than by one single gene. Therefore, when studying behavior, we should generally not think:
“One gene → one behavior.”
Instead, behavior is usually the result of a much more complicated interaction between:
many genes + past experiences + present environment + other biological processes →
behavior
Evolution by natural selection
Where do our parents' sets of genes come from?
Our parents inherited their genes from their parents, who inherited their genes from their
parents, and so on.
This means that the genetic information we have today has been passed down through
many generations.
Over very long periods of time, the genome of a population can change through evolution.
This idea is strongly associated with Charles Darwin and his theory of evolution.
Charles Darwin proposed that all modern organisms are descended from earlier organisms.
In other words, different species share common ancestors and have changed over many
generations through the process of evolution.
Natural selection
