Biological Psychology
LECTURE 1 Evolution genetics
Evolution, heredity and our DNA
Is there a depression gene?
“in most cases of depression, around 50% of the cause is genetic, and around 50% is unrelated to genes
(psychological or physical factors).”
But let’s start at the beginning....
Life on earth (Ma = million years)
4550 Ma: Formation of the Earth, 230-66 Ma: Non-avian dinosaurs, 2 Ma: First Homininis
Darwin→all organisms are related and share a common ancestor.
Natural selection→Those organisms that possess beneficial characteristics are more likely to survive and
reproduce.
Different from genetic modification→quicker form of selection, genes are added or deleted for the benefit of the
organism
Supporting evidence:
-Biogeography→best fit for their unique environment
-Fossil records→looking at different geological layers to chart evolution of species
-Structural similarity→common ancestor
-Embryology→similar stages in utero across species→during development, every organism goes through every
stage of its evolutionary past. past. As the embryo develops, these similarities are reduced.
-Molecular biology→elements of genes
Modern taxonomic groups from their common ancestor
Earth was created about 600 million years ago, 150 million years later organisms with nerves were evident,
surrounded by vertebrae (spine) → Life in the water was hard and some of these first incarnations of fish ventured
onto land=amphibians
Evolved legs and lungs=reptiles→Mammals evolved from reptiles about 10 million years ago (mammary glands)
Development in utero =greater safety and protection from harsh environments.
Humans are members of the family Hominines. Within this family, there are two genera: Australopithecus and
Homo. We come from the Homo group – humans are Homo sapiens (2 millions years ag0).
Y-chromosomal Adam and Mitochondrial Eve
Mitochondrial Eve, the most recent female-line common ancestor of all living people. "Y-chromosomal Adam", the
most recent male-line common ancestor of all living people — two individuals who passed down a portion of their
genomes to the vast expanse of humanity — are known as our most recent common ancestors, or MRCAs.
Descent of modern humans
Homo sapiens: one species
Y-chromosomal Adam: most recent common ancestor from whom all currently living people are descended
patrilineally Mitochondrial Eve: the most recent woman from whom all living humans are descended matrilineally
(via the mother) through
1
,transmission of mitochondrial DNA.
Q: From whom does a man inherit his mitochondria?
Out of Africa*: Homo sapiens migration *or Eurasia?
“the ancestry of most Eurasian men can be traced back to four ancestors who lived 50,000 years ago, who were
descendants of African.” →Migrating out of Africa to the rest of the world in search of resources
Increased use of tools=increase in brain volume→Brain most complex than chimpanzee/bonobo (other primates)
→important changes in the protein sequences in the human genome, together with duplication and deletion of
genes.
Brain=evolutionary development of the vertebrate’s spine.
Human brain→more sulci→greater volume to the cortex (=uniquely human)
Evolutionary psychology→address how certain pressures in the environment give rise to certain characteristics of
human behavior.
Behavioral genetics→2 types of heritable characteristics or traits:
-Qualitative traits→often influenced by a single gene and follow a simple pattern of inheritance, such as Mendelian
inheritance. Phenotypes are qualitatively different. Qualitative traits are typically unaffected by environmental
factors.
Sometimes individuals who have inherited disease-associated alleles do not always express the disease
completely or partially.
=allele with low penetrance
Mosaicism→when not all of the cells in the body are genetically identical via atypical cellular divisions during early
development, such as in Turner’s syndrome where there is a deletion of the X chromosome from the normal XX
genotype in some but not all of the cells (in females, absent or incomplete development at puberty, drooping
eyelids, short stature, producing little estrogen, and absence of menstrual period).
-Quantitative traits→influenced by multiple genes, polygenetic disorders→more variable and less
predictable→phenotype with a quantitative trait is expressed along a continuum. An example is ADHD. + it is
subject to alteration and migration by environmental factors.
Quantitative trait loci (QTL) →how many multiple genes at different locations on the chromosome contribute to the
quantitative trait.
Europeans have Neanderthal DNA...
Fractions of neanderthal dna are less likely to be related to schizophrenia → there are people who have less
neanderthal dna (african for example→Genotype A→Yoruba=West African ethnic group who mainly inhabit parts of
Nigeria, Benin and Togo)
A/B genotyped (Individual of European ancestry): having an admixture (combination) of Neanderthal (very little)
and Homo sapiens DNA
Examining A/B genotyped individuals compared to original DNA provides clues on evolution of human conditions
C=Primate
Relevance for psychology? Evolution of schizophrenia
Schizophrenia is present in about 1% of human populations around the world
• Heritability of schizophrenia is estimated to be up to 80%
• Genetics underlying schizophrenia risk emerged recently in hominid evolution
• If it emerged recently in homo sapiens, can it be that Neanderthal associated loci have a lower risk of
schizophrenia?
Significantly lower NeanderScore in individuals with schizophrenia (based on how their dna looks like, numbers)
Having more Neanderthal admixture (higher NeanderScore) was related to less severe positive symptoms of
schizophrenia (things that are added to our normal consciousness, seeing things that are not there)
Since modern human beings have it more=schizophrenia evolved more recently
Note: This method does not identify specific genes or genetic mechanisms that might drive the relationships; it only
documents that the genetic relationship exists.
2
,Human genetic variation
All humans are 99.9% genetically identical. The 0.1% genetic differences between humans makeup all differences.
In total our dna is 3 billion [miljard] nucleotides or ‘letters’ that make up the four-letter DNA alphabet [A-T - C-G]
< 2% of the DNA are functional genes coding for proteins
In total about 20,000 genes (instructions for making proteins) and the rest is helpful material, rest material
Polymorphisms→differences in DNA sequences among individuals present at a frequency greater than 1% of the
population.
Single nucleotide polymorphisms (SNPs)=larger polymorphisms that have large stretches of DNA
Each SNP represents a difference in a single nucleotide, e.g. cytosine (C) replaces thymine (T) in a particular
sequence of DNA.
Evolution: Natural selection in one slide
Traits becoming more common based on these key steps...
• Variation within species (e.g.tiny differences in DNA eg white color or dark color moth=dark so that birds don’t see
it to eat them) →mutation creates variation
• Heritability (pass it on to future generations if its helpful for survival and reproduction) • Struggle for existence
• Survival and reproductive rates (not everyone gets as many children and survives until they have reproduced)
Evolution in real-time:
Bacteria evolving resistance to antibiotics→they develop new mutations to survive the antibiotics, so bacteria that
are normally sensitive to antibiotics can evolve resistance to high concentrations in a short period of time
That’s lovely (if not potentially terrifying*), but what does it have to do with us? ...and with psychology?
*[What do you think happens with the effectiveness of antibiotics over time?]
Also I did not foresee the relevance of this video in 2017....since viruses also evolve.
Vaccines are very effective to prevent spreading and becoming severely ill but cannot completely prevent becoming
sick or spreading. Luckily mRNA vaccines can relatively easy be adapted to newer (resistant) variants of a virus
(immune lecture)
Major Depression and Genetics II
How do we know that genes play a role in causing depression?
Exploring role of genes (nature) versus environment (nurture)
Twin studies examining differences in monozygotic and dizygotic twins shed more light on heritable vs
environmental factors
• Monozygotic = identical DNA and shared environment (share same wound and placenta, same egg divided in 2)
• Dizygotic = DNA same as regular brother or sister, but with shared environment during gestation, birth,
development (same wound different placenta and egg, different sperma)
Q: Can you think of a study population which has a (largely) shared environment but different DNA? • Twin studies
examining
How do we know that genes play a role in causing depression?
Scientists look at patterns of illness in families to estimate their “heritability,” or roughly what % of their cause is due
to genes.
To do this we find people with the disease who have a twin, and then find out whether the twin is also ill. Identical
(monozygotic) twins share 100% of their genes, while non-identical (“fraternal” or dizygotic) twins share 50% of
their genes
• If genes are part of the cause, we expect a patient’s identical twin to have a much higher risk of disease than a
patient’s non-identical twin.
• That is the case for major depression.
• Heritability is probably 40-50%, and might be higher for severe depression→ the more severe the more likely
there are some genetic factors related to it
3
, Short summary I
• All humans belong to the same species: homo sapiens→Originated from African* ancestors about 200,000 years
ago
• Neanderthal and schizophrenia intermezzo
• Very much alike, small differences in letters in DNA determines all variation between humans
• Natural selection in one slide [read book for more details] • Evolution in real time (bacteria evolving resistance to
antibiotics)
• Depression gene and twin study (nature-nurture)
Human karyotype
• Karyotype: ‘organized’ set of chromosomes
• Karyotype of a human→ 46 chromosomes • 22 identical pairs from mother and father (diploid=paired, autosomes)
+ 1 set of ‘sex’ chromosomes (haploid)*
• Female: X and X chromosome (one from mom one from dad, depends on which chromosome is active and
which one is deactivated, eg. Y chromosome deactivated)
• Males: X and Y chromosome (*Real life is more varied than just these options. More on that in the sex
lecture)
DNA in the Cell
• Genome = the whole of the genetic information of an organism
• Chromosome = a long strand of DNA wound around histones
Centromere=a junction, not contain any genetic information, branches or arms referred to as p or q
• Telomere = region at the end of the chromosome, protects the DNA during cell division, stops so that the cell
cannot divide anymore and dies
Histones are proteins used to fold the DNA, so it doesn’t become entangled, can also be unwound
Gene = part of DNA with an instruction to make (a) protein(s)
Allele = the two alternative forms of a gene found at the same place on a chromosome (same gene: color of the
flower can have 2 variations: yellow or purple)
Genotype – Phenotype
Genotype is the genetic makeup of a cell in an organism (AA, Aa, aa)
Phenotype – observed trait in the organism, based on genes and environment (dark moth (AA/Aa) or light moth
(aa))
• Selection can occur for certain phenotypes
• Phenotype also sensitivity for food reward, becoming depressed, tendency to be persistent, chance to develop
diabetes
Mendelian genetics→whether the seed was coloured yellow or green (variant of color=trait)
Dominant trait→trait that appears in the first generation cross (AA)
Recessive trait→in second generation
The first-generation plants were carriers of the recessive trait (g1), but because it was combined with a dominant
trait (Y1) it was not observable. What is observed is phenotype and what is transmitted genetically is genotype.
Different color eyes:
4
LECTURE 1 Evolution genetics
Evolution, heredity and our DNA
Is there a depression gene?
“in most cases of depression, around 50% of the cause is genetic, and around 50% is unrelated to genes
(psychological or physical factors).”
But let’s start at the beginning....
Life on earth (Ma = million years)
4550 Ma: Formation of the Earth, 230-66 Ma: Non-avian dinosaurs, 2 Ma: First Homininis
Darwin→all organisms are related and share a common ancestor.
Natural selection→Those organisms that possess beneficial characteristics are more likely to survive and
reproduce.
Different from genetic modification→quicker form of selection, genes are added or deleted for the benefit of the
organism
Supporting evidence:
-Biogeography→best fit for their unique environment
-Fossil records→looking at different geological layers to chart evolution of species
-Structural similarity→common ancestor
-Embryology→similar stages in utero across species→during development, every organism goes through every
stage of its evolutionary past. past. As the embryo develops, these similarities are reduced.
-Molecular biology→elements of genes
Modern taxonomic groups from their common ancestor
Earth was created about 600 million years ago, 150 million years later organisms with nerves were evident,
surrounded by vertebrae (spine) → Life in the water was hard and some of these first incarnations of fish ventured
onto land=amphibians
Evolved legs and lungs=reptiles→Mammals evolved from reptiles about 10 million years ago (mammary glands)
Development in utero =greater safety and protection from harsh environments.
Humans are members of the family Hominines. Within this family, there are two genera: Australopithecus and
Homo. We come from the Homo group – humans are Homo sapiens (2 millions years ag0).
Y-chromosomal Adam and Mitochondrial Eve
Mitochondrial Eve, the most recent female-line common ancestor of all living people. "Y-chromosomal Adam", the
most recent male-line common ancestor of all living people — two individuals who passed down a portion of their
genomes to the vast expanse of humanity — are known as our most recent common ancestors, or MRCAs.
Descent of modern humans
Homo sapiens: one species
Y-chromosomal Adam: most recent common ancestor from whom all currently living people are descended
patrilineally Mitochondrial Eve: the most recent woman from whom all living humans are descended matrilineally
(via the mother) through
1
,transmission of mitochondrial DNA.
Q: From whom does a man inherit his mitochondria?
Out of Africa*: Homo sapiens migration *or Eurasia?
“the ancestry of most Eurasian men can be traced back to four ancestors who lived 50,000 years ago, who were
descendants of African.” →Migrating out of Africa to the rest of the world in search of resources
Increased use of tools=increase in brain volume→Brain most complex than chimpanzee/bonobo (other primates)
→important changes in the protein sequences in the human genome, together with duplication and deletion of
genes.
Brain=evolutionary development of the vertebrate’s spine.
Human brain→more sulci→greater volume to the cortex (=uniquely human)
Evolutionary psychology→address how certain pressures in the environment give rise to certain characteristics of
human behavior.
Behavioral genetics→2 types of heritable characteristics or traits:
-Qualitative traits→often influenced by a single gene and follow a simple pattern of inheritance, such as Mendelian
inheritance. Phenotypes are qualitatively different. Qualitative traits are typically unaffected by environmental
factors.
Sometimes individuals who have inherited disease-associated alleles do not always express the disease
completely or partially.
=allele with low penetrance
Mosaicism→when not all of the cells in the body are genetically identical via atypical cellular divisions during early
development, such as in Turner’s syndrome where there is a deletion of the X chromosome from the normal XX
genotype in some but not all of the cells (in females, absent or incomplete development at puberty, drooping
eyelids, short stature, producing little estrogen, and absence of menstrual period).
-Quantitative traits→influenced by multiple genes, polygenetic disorders→more variable and less
predictable→phenotype with a quantitative trait is expressed along a continuum. An example is ADHD. + it is
subject to alteration and migration by environmental factors.
Quantitative trait loci (QTL) →how many multiple genes at different locations on the chromosome contribute to the
quantitative trait.
Europeans have Neanderthal DNA...
Fractions of neanderthal dna are less likely to be related to schizophrenia → there are people who have less
neanderthal dna (african for example→Genotype A→Yoruba=West African ethnic group who mainly inhabit parts of
Nigeria, Benin and Togo)
A/B genotyped (Individual of European ancestry): having an admixture (combination) of Neanderthal (very little)
and Homo sapiens DNA
Examining A/B genotyped individuals compared to original DNA provides clues on evolution of human conditions
C=Primate
Relevance for psychology? Evolution of schizophrenia
Schizophrenia is present in about 1% of human populations around the world
• Heritability of schizophrenia is estimated to be up to 80%
• Genetics underlying schizophrenia risk emerged recently in hominid evolution
• If it emerged recently in homo sapiens, can it be that Neanderthal associated loci have a lower risk of
schizophrenia?
Significantly lower NeanderScore in individuals with schizophrenia (based on how their dna looks like, numbers)
Having more Neanderthal admixture (higher NeanderScore) was related to less severe positive symptoms of
schizophrenia (things that are added to our normal consciousness, seeing things that are not there)
Since modern human beings have it more=schizophrenia evolved more recently
Note: This method does not identify specific genes or genetic mechanisms that might drive the relationships; it only
documents that the genetic relationship exists.
2
,Human genetic variation
All humans are 99.9% genetically identical. The 0.1% genetic differences between humans makeup all differences.
In total our dna is 3 billion [miljard] nucleotides or ‘letters’ that make up the four-letter DNA alphabet [A-T - C-G]
< 2% of the DNA are functional genes coding for proteins
In total about 20,000 genes (instructions for making proteins) and the rest is helpful material, rest material
Polymorphisms→differences in DNA sequences among individuals present at a frequency greater than 1% of the
population.
Single nucleotide polymorphisms (SNPs)=larger polymorphisms that have large stretches of DNA
Each SNP represents a difference in a single nucleotide, e.g. cytosine (C) replaces thymine (T) in a particular
sequence of DNA.
Evolution: Natural selection in one slide
Traits becoming more common based on these key steps...
• Variation within species (e.g.tiny differences in DNA eg white color or dark color moth=dark so that birds don’t see
it to eat them) →mutation creates variation
• Heritability (pass it on to future generations if its helpful for survival and reproduction) • Struggle for existence
• Survival and reproductive rates (not everyone gets as many children and survives until they have reproduced)
Evolution in real-time:
Bacteria evolving resistance to antibiotics→they develop new mutations to survive the antibiotics, so bacteria that
are normally sensitive to antibiotics can evolve resistance to high concentrations in a short period of time
That’s lovely (if not potentially terrifying*), but what does it have to do with us? ...and with psychology?
*[What do you think happens with the effectiveness of antibiotics over time?]
Also I did not foresee the relevance of this video in 2017....since viruses also evolve.
Vaccines are very effective to prevent spreading and becoming severely ill but cannot completely prevent becoming
sick or spreading. Luckily mRNA vaccines can relatively easy be adapted to newer (resistant) variants of a virus
(immune lecture)
Major Depression and Genetics II
How do we know that genes play a role in causing depression?
Exploring role of genes (nature) versus environment (nurture)
Twin studies examining differences in monozygotic and dizygotic twins shed more light on heritable vs
environmental factors
• Monozygotic = identical DNA and shared environment (share same wound and placenta, same egg divided in 2)
• Dizygotic = DNA same as regular brother or sister, but with shared environment during gestation, birth,
development (same wound different placenta and egg, different sperma)
Q: Can you think of a study population which has a (largely) shared environment but different DNA? • Twin studies
examining
How do we know that genes play a role in causing depression?
Scientists look at patterns of illness in families to estimate their “heritability,” or roughly what % of their cause is due
to genes.
To do this we find people with the disease who have a twin, and then find out whether the twin is also ill. Identical
(monozygotic) twins share 100% of their genes, while non-identical (“fraternal” or dizygotic) twins share 50% of
their genes
• If genes are part of the cause, we expect a patient’s identical twin to have a much higher risk of disease than a
patient’s non-identical twin.
• That is the case for major depression.
• Heritability is probably 40-50%, and might be higher for severe depression→ the more severe the more likely
there are some genetic factors related to it
3
, Short summary I
• All humans belong to the same species: homo sapiens→Originated from African* ancestors about 200,000 years
ago
• Neanderthal and schizophrenia intermezzo
• Very much alike, small differences in letters in DNA determines all variation between humans
• Natural selection in one slide [read book for more details] • Evolution in real time (bacteria evolving resistance to
antibiotics)
• Depression gene and twin study (nature-nurture)
Human karyotype
• Karyotype: ‘organized’ set of chromosomes
• Karyotype of a human→ 46 chromosomes • 22 identical pairs from mother and father (diploid=paired, autosomes)
+ 1 set of ‘sex’ chromosomes (haploid)*
• Female: X and X chromosome (one from mom one from dad, depends on which chromosome is active and
which one is deactivated, eg. Y chromosome deactivated)
• Males: X and Y chromosome (*Real life is more varied than just these options. More on that in the sex
lecture)
DNA in the Cell
• Genome = the whole of the genetic information of an organism
• Chromosome = a long strand of DNA wound around histones
Centromere=a junction, not contain any genetic information, branches or arms referred to as p or q
• Telomere = region at the end of the chromosome, protects the DNA during cell division, stops so that the cell
cannot divide anymore and dies
Histones are proteins used to fold the DNA, so it doesn’t become entangled, can also be unwound
Gene = part of DNA with an instruction to make (a) protein(s)
Allele = the two alternative forms of a gene found at the same place on a chromosome (same gene: color of the
flower can have 2 variations: yellow or purple)
Genotype – Phenotype
Genotype is the genetic makeup of a cell in an organism (AA, Aa, aa)
Phenotype – observed trait in the organism, based on genes and environment (dark moth (AA/Aa) or light moth
(aa))
• Selection can occur for certain phenotypes
• Phenotype also sensitivity for food reward, becoming depressed, tendency to be persistent, chance to develop
diabetes
Mendelian genetics→whether the seed was coloured yellow or green (variant of color=trait)
Dominant trait→trait that appears in the first generation cross (AA)
Recessive trait→in second generation
The first-generation plants were carriers of the recessive trait (g1), but because it was combined with a dominant
trait (Y1) it was not observable. What is observed is phenotype and what is transmitted genetically is genotype.
Different color eyes:
4
