Evolution, genes, environment & behaviour (chapter 3)

Question 1

What do genes carry the blueprint for?

Answer 1

Making our whole body, including the brain

Question 2

What are half of our genes estimated to target?

Answer 2

Brain structure and function (Kolb & Whishaw, 2003)

Question 3

What is behavioural genetics?

Answer 3

A field of psychological science dedicated to investigating how genes and the environmental factors interact during the course of development so as to affect behaviour

Question 4

What is evolutionary psychology?

Answer 4

A field of psychological science that investigates the evolutionary origins of various psychological traits

Question 5

What do evolutionary psychologists argue?

Answer 5

That important aspects of human psychology and social behaviour, including aggression, altruism, nepotism, and mate choice , are influenced by evolved biological mechanisms

Question 6

What is evolution (biological)?

Answer 6

Gradual change over time in organic life from one form into another

Question 7

What does the theory of evolution suggest?

Answer 7

That life on Earth has been subject to a low, but inexorably powerful, process of change

Question 8

What is natural selection?

Answer 8

Characteristics that increase the likelihood of survival and reproduction within a particular environment will be preserved in the population and therefore become more frequent over time

Question 9

What is natural selection based on? (3)

Answer 9

It is an undirected/’blind’ process based on three factors:

1) biological variation
2) high reproduction rates and the fact that not all members of a population survive
3) competition over limited resources (Lewin, 2005)

Question 10

What might some of these biological differences convey?

Answer 10

An advantage in terms of survival and reproduction. E.g. some members of a particular prey species may possess more acute hearing than others and hence be better able to detect and avoid predators

Question 11

What can happen if adaptive traits are heritable?

Answer 11

They can be biologically passed on from parent to infant, and over time they will increase in frequency in the population

Question 12

What does natural selection affect?

Answer 12

Not just physiological features (such as degree of furriness) but also behavioural traits

Question 13

What can be seen, behaviourally, when the genomes of dogs and wolves are compared? (experimental evidence)

Answer 13

The largest areas of difference were related to brain function and nervous system development. Other findings concerning differences in interaction with humans.
These findings cannot be easily explained in terms of differences in learning or experience, since both species in the experiment were raised in a similar manner. Thus it would seem that certain behaviours, such as visually orienting to humans, are under the influence of inherited biological factors.

Question 14

How do new traits emerge in a population if organisms faithfully inherit parental characteristics?

Answer 14

Genetic mutation

Question 15

What are mutations?

Answer 15

Random events and accidents in gene reproduction during the division of cells

Question 16

What do mutations do?

Answer 16

Help create variation within a population’s physical and behavioural characteristics. It is this genetic variation that makes evolution possible.

Question 17

What is the blending theory?

Answer 17

Blending suggests that parental traits are blended together rather like mixing white and red paint to produce pink

Question 18

What is a problem with blending?

Answer 18

It is incompatible with natural selection (Jenkin, 1867)
Blending traits eliminates variability. Without variability, natural selection cannot operate because it has nothing to select among. Thus, one would end up with the mean or average pattern and any behavioural differences would be due to learning from the environment.

Question 19

Who solved the puzzle of inheritance?

Answer 19

an Austrian monk, Gregor Mendel in the 1860s

Question 20

How were the laws of inheritance worked out?

Answer 20

Through conducting elegant experiments on pea plants. Mendel used a pea plant which produces either all green, all yellow or a mixture of green and yellow peas

Question 21

How did Mendel carry the experiments out?

Answer 21

Used a baseline parent generation (P). He prevented them from self-fertilizing and manually cross-fertilized them. The resultant peas in the following generation (F1) were all yellow: the green characteristic had completely disappeared. He then planted the F1 generation and allowed the resultant plants to self-fertilize. The F2 peas showed that the green trait had re-emerged in an overall ratio of 3 yellow:1 green. He then left these to self fertilise and found that of this generation (F3), the green peas grew into plants which only produced green peas , one third of the yellow plants produced all yellow peas and the remaining plants produced the same 3:1 ratio again.

Question 22

What did Mendel propose following his findings?

Answer 22

That the yellow was the dominant trait, and the green was recessive. Furthermore, as the yellow peas from the cross-fertilized plants grew into plants that produced both green and yellow peas, they must still have been carrying the green trait, but unexpressed. Mendel proposed that heredity factors (genes) must come in double doses - each of which is called an allele. The particular combination of dominant and recessive alleles determines the outwardly expressed characteristic of an organism or its phenotype.

Question 23

What is a dominant characteristic?

Answer 23

The particular characteristic that it controls will be displayed (AA)

Question 24

What is a recessive characteristic?

Answer 24

The characteristic will not show up unless the partner gene inherited from the other parent is also recessive (aa)

Question 25

What is an allele?

Answer 25

Alternative forms of a gene that produce different characteristics

Question 26

How to gametes differ from other cells?

Answer 26

They only carry one allele.

Question 27

How do the complementary pairs of alleles come together from sex cells?

Answer 27

They come together in different combinations during fertilization. Organisms that receive the same alleles, that is, two dominant or two recessive, for a trait are called homozygous and organisms with different forms of alleles, one dominant and once recessive, are called heterozygous

Question 28

What does homozygous mean?

Answer 28

Organisms that possess the same type of allele for a trait, either two dominant or two recessive

Question 29

What does heterozygous mean?

Answer 29

Organisms that possess different allele for a trait, one dominant and one recessive

Question 30

What is the genotype?

Answer 30

The specific and complete genetic make-up of the individual

Question 31

What is the phenotype

Answer 31

The individual’s outward observable characteristics

Question 32

When is genotype present from?

Answer 32

Conception

Question 33

What is phenotype affected by?

Answer 33

By both other genes and the environment. The same phenotype can have different genotypes.

Question 34

How can the same genotype have the same phenotypes?

Answer 34

Identical twins have the same genes, but if one eats more than the other they will differ in the phenotypic expression of body weight.

Question 35

What are Phenylketonuria and Huntington’s disease (relation to genes)?

Answer 35

They are directly relevant psychological conditions which manifest themselves primarily in terms of psychological malfunctioning. They are both based upon the inheritance of specific combinations of the alleles from single genes

Question 36

What is Phenylketonuria (PKU)?

Answer 36

PKU is associated with developmental delay and severe learning difficulties (Williams et al., 2008). It occurs at a rate of approximately 1 in 10,000 births. Often parents of children with PKU do not exhibit the condition. It runs in families and it tends to occur at a higher incidence in small, inbred communities (sometimes referred to as the Kissing Cousins Disease)

Question 37

What is PKU based on/how is it inherited?

Answer 37

It is based on the inheritance of a double dose of recessive alleles (pp).
If a parent is homozygous for the dominant allele (PP), they cannot pass on the disorder.
If one parent was a carrier (Pp) and the other parent is not (PP), none of their children will develop the disorder, but there is a 50% chance that they will be a carrier.
If both parents are carriers, they themselves will not have the disorder, but their offspring will have a 25% chance of inheriting two recessive alleles and being born with PKU

Question 38

What is Huntington’s disease?

Answer 38

A degenerative disorder in which the sufferer experiences personality changes along with decreasing mental, memory and movement functioning over time. It affects 1 in 20,000 people. The average age of onset is 40 years old and generally one parent has the condition and his/her children have a 50% chance of passing it onto their children (Plomin et al., 2013)

Question 39

What is Huntington’s based on/how is it inherited?

Answer 39

HD is based upon the inheritance of a dominant allele; so that the inheritance of the condition is somewhat similar to that found with yellow peas. Unaffected individuals have two recessive alleles, while affected individuals have usually inherited one of the dominant alleles from their affected parent.
Statistically, it would be very unlikely that two heterozygous (Hh) for HD would meet and have children, however if this did occur then their children would have a 75% chance of developing the condition, with a 50% chance of the child being heterozygous (Hh) for the condition, and a 25% chance of them inheriting a double dose of the dominant allele (HH)

Question 40

Why does HD remain in the population?

Answer 40

Because of its late onset. Since the disorder does not being to manifest itself until the affected individual is around 40 years of age, and by that time they will often have had children. Those children will have a 50:50 chance of inheriting the dominant allele from their affected parent and so in turn eventually manifest the symptoms of HD

Question 41

What are genes?

Answer 41

Genes are functional segments of a long molecule called deoxyribonucleic acid or DNA

Question 42

What does each gene carry?

Answer 42

The chemical code for manufacturing specific proteins, as well as the codes for when and where in the body they will be made

Question 43

What can proteins do?

Answer 43

Proteins can take many forms and functions, and they underlie every bodily structure and chemical process. For that reason, DNA has been described as the blueprint for the body.

Question 44

Since the mapping of the entire human genome, how many genes are humans thought to have?

Answer 44

It is now thought that humans have around 20,000 genes. The average gene has about 3,000 chemical base pairs, but sizes vary greatly; the largest gene has 2.4 million bases. It is estimated that about half of all genes target brain structure and functions.

Question 45

What is a chromosome?

Answer 45

A single or double stranded structure comprised of proteins and deoxyribonucleic acid (DNA)

Question 46

Where are chromosomes found?

Answer 46

They are only found within a cell’s nucleus. They come in pairs.

Question 47

What form do chromosomes take?

Answer 47

They take the form of a single strong or rod (called a chromatid) until they copy themselves prior to cell division, which is when they assume their iconic X-like shape.

Question 48

What are chromosomes comprised of?

Answer 48

Proteins and DNA. Histone proteins are tiny structures around which the string of DNA is wound rather like thread on a cotton reel. If unravelled, the DNA molecule, although invisible to the naked eye, would be approximately 6 feet or 2 meters long.

Question 49

What is a somatic cell?

Answer 49

A somatic cell is any cell forming the body of an organism. They do not contain reproductive cells.

Question 50

What do all non-sex or somatic cells contain?

Answer 50

The diploid number of chromosome, which constitutes the full complement with both members of each pair being present (except for red blood cells that have no nucleus)

Question 51

What do sex cells or gametes contain?

Answer 51

The haploid number of chromosomes comprised of only one of each of the pairs from one or other of the parents, that is, 23 in humans.

Question 52

What does diploid mean?

Answer 52

Diploid is a cell consisting of two sets of chromosomes

Question 53

What does haploid mean?

Answer 53

Haploid is half the number of chromosomes found in a gamete

Question 54

What is a gamete?

Answer 54

Sex cells (eggs and sperm)

Question 55

What is a zygote?

Answer 55

A zygote is a fertilized egg containing 46 pairs of chromosomes

Question 56

What happens when the human egg and sperm combine?

Answer 56

The fertilized egg or zygote contains all 46 chromosomes, with one of each pair coming from the father and its complementary pair from the mother. The fact that there are complementary pairs of chromosomes relates to alleles. Each gene is represented twice (i.e. as alleles) at the same locus (which is Latin for place; the plural is loci) on each of the chromosome pairs.

Question 57

What are chromosomes made of?

Answer 57

Made of two substances: nucleic acids and proteins.

Proteins are much more varied than nucleic acids. They are molecules made of chains of approximately 100 amino acids.

Question 58

What does the precise order or amino acids along the chain determine?

Answer 58

The type of protein. There are 20 kinds of amino acids, thus there are 20 to the 100 possible combinations (20 to the 100 is more than the total number of atoms in the universe. Since there are so many potential proteins, initially scientists thought that proteins must contain the heredity code. instead, the code for life is found in the nucleic acid, DNA

Question 59

Why does DNA have a distinctive structure?

Answer 59

Discovered by Watson and Crick (largely based on the experimental work of Wilkins and Franklin in the early 1950s), it has a geometric shape of a double helix, which looks a bit like a twisted ladder. The rails of the ladder are made up of alternating sugar and phosphate molecules. The rungs are made up of pairs of four chemical or nitrogenous bases - adenine (A), thymine (T), guanine (G) and cytosine (C). It is as if the ladder rungs are made of two halves locked together: the chemical base guanine is always opposite cytosine, and adenine is always opposite thymine.

Question 60

How does DNA allow for very accurate copying?

Answer 60

During replication, the two halves of the ladder split lengthways down the centre and each half can be used as a template to reconstruct the whole again. When the ladder is split, free-floating nucleotides in the cell are attracted to their complementary open bases on the DNA strand. It is rather like a self-assembling, four-piece, 3D jigsaw

Question 61

What are nucleotides?

Answer 61

Nitrogenous base, phosphate and sugar groups

Question 62

What is a codon?

Answer 62

A non-overlapping triplet sequence of nucleotides

Question 63

What creates the specific commands to make functions in your body?

Answer 63

The sequence of the four letters of the DNA alphabet (A,T,G and C) creates the specific, commands for every feature and function of your body. The basic unit of the genetic code is made up of non-overlapping triplet sequences of nucleotides each of which is called a codon. With four different ‘letters’ of the DNA alphabet being read in non-overlapping triplet sequences, there are 64 possible combinations or permutations, 444.

Question 64

What are the two type of statements that the triplet sequences can make?

Answer 64

One type specifies an amino acid and the other signals ‘stop’ in the sense that it stops the process of ‘translating’ a gene. With 20 types of amino acid and a stop sign, the total number of statements needed is 21. With 64 possible permutations, there is a great deal of overlap in the triplet code so that nearly every type of amino acid is specified by more than one codon.

Question 65

What other kind of nucleic acid helps with DNA transcription?

Answer 65

Ribonucleic acid or RNA. RNA has a simpler structure than DNA. It is comprised of a single strand of nucleotides. In addition, instead of the sugar being deoxyribose as it is with DNA, it is ribose in RNA. RNA has the same nitrogenous bases as DNA except that instead of thymine it has uracil

Question 66

Where does transcription begin?

Answer 66

In the nucleus of he cell

Question 67

What happens in transcription?

Answer 67

A section of DNA unzips itself exposing the nitrogenous bases of a gene. The nucleotides of messenger RNA (mRNA) are attracted to their complimentary bases and they form into a continuous strand along the length of the gene.
This strand of mRNA then travels out of the nucleus into the cytoplasm of the cell. A large molecule called ribose then travels along the length of the mRNA activating its codons as it goes. When a codon is activated, transfer RNA (tRNA), which is floating loose in the cytoplasm, fixes itself to its complementary codon, rather like a three-pronged key fitting into a lock. Specific amino acids are attached to the surface of particular types of tRNA. The particular amino acids from each tRNA bond together and forma chain.
This chain will fold into a particular shape depending on the order of the different types of amino acids along its length. The shape that the amino acids form determines the specific type of protein they become. Transcription is a very complex process.

Question 68

What is the most important thing to understand about genetic transcription?

Answer 68

That the end product is a protein

Question 69

Why are statements like “a gene for eye colour” and “a gene for autism” technically incorrect?

Answer 69

Since genes primarily code for proteins, it is not technically correct to state that there is a gene for any time of phenotypic feature. Genes influence phenotypic expression in a more indirect manner. Nonetheless, since proteins are involved in every structure of the body (including the brain) DNA has a profound effect on our cognitive processing, personality and behaviour

Question 70

What does it mean when a condition or trait is monogenic?

Answer 70

They are based upon the influence of one gene

Question 71

What is polygenic transmission?

Answer 71

When a number of gene pairs combine their influences to create a single phenotypic trait

Question 72

What does polygenic transmission do (compared with monogenic transmission)?

Answer 72

It complicates the straightforward picture that would occur if all characteristics were determined by one pair of genes. It also magnifies the number of possible variations in a trait than can occur.

Question 73

How many estimated genotypes can occur when a sperm and an egg joins together?

Answer 73

Despite the fact that about 99.9% of human genes are identical among people, it is estimated that the union of a sperm and egg cell can result in about 70 trillion potential genotypes, accounting for the great diversity of characteristics that occurs even among siblings

Question 74

What does behaviourism assume?

Answer 74

That there are laws of learning that apply to virtually all organisms. Behaviourists treated the organism as a ‘tabula rasa’, or a blank slate, on which learning experiences were inscribed. Most of their research was conducted with non-human species in controlled laboratory settings. Behaviourists explained learning solely in terms of directly observable events and avoided speculating about an organism’s mental state.

Question 75

What do ethologists focus on?

Answer 75

Animal behaviour in the natural environment, viewing the organism as much more than a blank slate, and arguing that, because of evolution, every species comes into the world biologically prepared to act in certain ways. Thus, they possess inherited behavioural adaptations

Question 76

What are inherited behavioural adaptations?

Answer 76

Traits that organisms are born with that help promote their chances of survival and reproductive success

Question 77

What is a fixed action pattern (FAP)?

Answer 77

An unlearned response automatically triggered by a particular stimulus.

Question 78

What is releasing stimuli?

Answer 78

External stimuli that trigger fixed action patterns

Question 79

Give an example of FAP and realising stimuli —

see page 90 - Tinbergen

Answer 79

Niko Tinbergen suspected that the chicks enter the world with an innate fixed action pattern of pecking that could be triggered by pre-programmed releasing stimuli.

Question 80

What is a superstimulus?

Answer 80

An exaggerated version of a releasing stimulus that triggers a stranger response than the naturalistic model

Question 81

What became increasingly clear as ethology research proceeded?

Answer 81

That even quite apparently rigid behaviour such as fixed actions patterns is subject to refinement by learning. E.g. animal behaviour being a natural instinct but copied from adults and therefore refined

Question 82

What does environment mean?

Answer 82

Environment is a very broad term, referring to everything from the prenatal world of the womb and the simplest physical environment to the complex social systems in which we interact with multiple people, places and things.

Question 83

What is a shared environment?

Answer 83

The people who reside in these experience many of their features in common. E.g. environments such as family household or school classroom are shared with people such as siblings and classmates and as such they have many features in common.
Siblings living in the same home are exposed to a common physical environment, the availability and unavailability of books, a television or a computer. They share the quality of food in the home, exposure to the attitudes and other values transmitted by parents, and many other experiences.

Question 84

What is an unshared environment?

Answer 84

Experiences that are unique to us. Even children in the same home have their own unique experience, including distinct relationships with their parents and siblings.

Question 85

What type of study is particularly useful in studying group variance?

Answer 85

Twin studies (especially those that include twins raised together and apart) are particularly useful in estimating the extent to which genotype, shared environment and unshared environment contribute to group variance on a particular characteristic.

Question 86

What is behavioural genetics?

Answer 86

How heredity and environmental factors influence psychological characteristics

Question 87

What are behavioural geneticists trying to determine?

Answer 87

Try to determine the relative influence of genetic and environmental factors in accounting for individual differences in behaviour. E.g. a common question posed by behavioural geneticists is ‘how important are genetic factors in aggression, intelligence, personality characteristics and various types of psychological disorders?’

Question 88

In what two ways can genetic similarity be expressed?

Answer 88

First, we can take equivalent sections of DNA between different humans or different species and calculate the degree of similarity between base pairs. According to such comparisons, we share around 98-99% of our DNA code with chimpanzees and about 99.9% with other unrelated humans.
Second, we can express genetic differences in terms of the inheritance of specific alleles from our parents. We directly inherit half our alleles from our mother and the other half from our father. Thus we receive 50% of each of our parents’ genes by direct common descent.

Question 89

What does degree of relatedness mean?

Answer 89

The number of genes we share with others by direct common descent

Question 90

Outline the probability of sharing genes with parents and siblings —

Answer 90

The probability of sharing any particular gene with one of your parents is 50% or .50. If you have siblings, you also have .50 probability of sharing the same gene by common decent with each of them. Identical twins share the same genotype and thus have a 1.00 probability of sharing any particular twin. The probability of having a shared gene with a grandparent is .25 as half was passed onto your parent and then half to you. The probability of sharing a gene with a half-sibling is .25 also. First cousins share .125 of genes (mothers siblings share .50, you share .25 with your aunt and half of that with their children, .125)

Question 91

What is concordance and what does having a high concordance rate mean?

Answer 91

concordance is co-occurrence. If a characteristic has higher concordance, or co-occurrence, in people who are more closely related to one another compared to unrelated individuals, this points to a possible genetic contribution, particularly if the people have lived in different environments.

Question 92

What are adoption studies?

Answer 92

People who were adopted early in life are compared on some characteristic both with their biological parents, with whom they share genetic endowment, and with their adoptive parents, with whom they share no genes

Question 93

What can adoption studies show?

Answer 93

If adopted people are more similar to a biological parent (with whom they share 50% of their genes) than to an adoptive parent (with whom they share a common environment but no genes), a genetic influence on a trait is indicated. If they are more similar to their adoptive parents, environmental factors are judged to be more important for that particular characteristic. (E.g. study showing a hereditary link with schizophrenia).

Question 94

What are twin studies?

Answer 94

Twin studies compare trait similarities in identical and fraternal twins

Question 95

How are twin studies important?

Answer 95

They are one of the more powerful techniques used in behavioural genetics. Because monozygotic, or identical twins develop from the same fertilized egg, they are genetically identical. Approximately 1 in 250 births produces identical twins. Dizygotic, or fraternal, twins develop from two fertilized eggs, so they share 50% off their genetic endowment, like any other set of siblings Approximately 1 in every 150 births produces fraternal twins

Question 96

What are concordance rates?

Answer 96

Statistical expression of the probability that two individuals with shared genes will share a particular trait to the same degree

Question 97

What can we assume in twin studies?

Answer 97

We assume that if the identical twins are far more similar to one another than the fraternal twins are on a specific characteristic, a genetic factor is likely to be involved.

Question 98

What is a key drawback of twin studies?

Answer 98

Of course, the drawback is the possibility that because identical twins ae more similar to one another in appearance than fraternal twins are, they are treated more alike and therefore share a more similar environment. This could partially account for greater behavioural similarity in identical twins.

Question 99

What have behavioural geneticists done to rule out the environmental explanation?

Answer 99

They have adopted an even more elegant research method. Sometimes researchers are able to find and compare sets of identical and fraternal twins who were separated very early in life and raised in different environments. By eliminating environmental similarity, this research design permits a better basis for evaluating the respective contributions of genes and environment

Question 100

What tends to be found with twin & adoption studies?

Answer 100

Many (but not all) psychological characteristics, including intelligence, personality traits and certain psychological disorders, have a notable genetic contribution. Adopted children are typically found to be more similar to their biological parents than to their adoptive parents on these measures, and identical twins tend to be more similar to one another than fraternal twins, even if they were separated in early life and reared in different environments. On the other hand, identical twins reared together still tend to be somewhat more similar for some characteristics than those reared apart, indicating that the environment also makes a difference

Question 101

What does a heritability coefficient do?

Answer 101

It estimates the extent to which the differences, or variation, in a specific phenotypic characteristic within a group of people can be attributed to their differing genes

Question 102

What does heritability only apply to?

Answer 102

It only applies to differences within the particular group tested and estimates can and do vary, depending on the group

Question 103

How are heritability coefficients estimated?

Answer 103

Subtracting each heritability coefficient from 1 provides an estimate of the proportion of variability in the particular group tested that is attributable to the environment in which they developed.
For example, for height, environment only accounts for only abut 1 minus .9, a proportion of .1 (or 10%), of the variation within the group, but for individual difference in preferred characteristics in a mate, environment accounts for virtually all differences among the people tested

Question 104

What do behavioural geneticists realise in terms of genes and environment?

Answer 104

Even while they try to estimate the contributions of genetic factors, they realise that genes and environment are not really separate determinants of behaviour. Instead, they operate as a single, integrated system. Gene expression is influenced on a daily basis by the environment.
E.g. 2 children of equal intellectual potential may have differences in IQ as great as 15 to 20 points if one is raised in an impoverished environment and the other in an enriched environment.

Question 105

What can environmental stress do?

Answer 105

High or low environmental stress can be responsible for turning on or off genes that regulate the production of stress hormones

Question 106

How do we have predispositions to certain disorders?

Answer 106

The genetic influence on certain psychological disorders can be very significant, including a disposition for schizophrenia and autistic spectrum disorders. It is our genetics that provide some of us with a predisposition to suffer with a problem. This is certainly true of depression. Of course, a predisposition (or diathesis) to suffer with something does not mean that you certainly will, jut that it may happen given the correct experiences, and environment.

Question 107

Examine the genetic argument of intelligence —

Answer 107

Suppose that intelligence were totally heritable, that is, suppose that 100% of the intellectual variation in the population were determined by genes. In that case, any two individuals with the same genotype would have identical intelligence test scores, so the correlation in the IQ between identical (monozygotic) twins would be 1.00. Non-identical brothers and sisters (including fraternal/dizygotic) twins share only half their genes. Therefore, the correlation between the test scores of fraternal twins and other siblings should be substantially lower. Extending the argument, the correlation between a parent’s test scores and his/her children’s scores should be about the same as that between siblings, because a child inherits only half of his/her genes from each parent

Question 108

Examine the correlation of intelligence regarding the genetic argument —

Answer 108

The correlation between the test scores of identical twins is substantially higher than any other correlations, but they are not 1.00. Identical twins separated early in life and reared apart are of special interest because they have identical genes but experienced different environments. It is important to note that the correlation for identical twins raised apart is nearly as high as that for identical twins reared together. It is also higher than that for fraternal twins raised together. This pattern of findings is a powerful argument for the importance of genetic factors.

Question 109

Looking at adoption studies, how large a factor is heritability in individual differences in intelligence?

Answer 109

IQs of adopted children correlate as highly with their biological parents’ IQs as they do with the IQs of the adoptive parents who reared them. Overall, the pattern is quite clear: the more genes people have in common, the more similar their IQs tend to be. This is very strong evidence that genes play a significant role in intelligence, accounting for 50 to 70% of group variation in IQ. However, analysis of the human genome shows that there clearly is not a single ‘intelligence’ gene. The diverse abilities measured by intelligence tests are undoubtedly influenced by large numbers of interacting genes, and different combinations seem to underlie specific abilities.

Question 110

Why isn’t the genetic argument of intelligence accepted alone?

Answer 110

Because genotype accounts for only 50 to 70% of the IQ variation among the individuals in these studies, genetics research provides a strong argument for the contribution of environmental factors to intelligence. Good places to look for such factors are in the home and school environments.

Question 111

How important to intelligence level is the shared environment of the home in which people are raised?

Answer 111

If home environment is an important determinant of intelligence, then children who grow up together should be more similar than children who are reared apart. Research shows that siblings who were raised together were indeed more similar to one another than those reared apart, whether they were identical twins or biological siblings.
Note also that there was a correlation of .32 between unrelated adopted children reared in the same home. Overall, it appears that between a quarter and a third of the individual differences in intelligence found in these particular groups could be attributed to shared environmental factors.

Question 112

What other additional factor may be important in influencing intelligence alongside the home environment?

Answer 112

Recent research suggests that differences within home environments are much more important at lower socioeconomic levels than they are in upper class families. This may be because lower socioeconomic families differ more among themselves in the intellectual richness of the home environment than do upper class families. Indeed, a lower-income family that has books in the house, cannot afford video games and encourages academic effort may be a very good environment for a child with good intellectual potential.

Question 113

How does environmental enrichment and deprivation influence environmental affected intelligence?

Answer 113

A line of evidence for environmental effects comes from studies of children who are removed from deprived environments and placed in middle or upper class adoptive homes. Typically such children show a gradual increase in IQ in the order of 10 to 12 points. Conversely, when deprived children remain in their impoverished environments, they either show no improvement in IQ or they actually deteriorate intellectually over time. Scores on general intelligence tests correlate around .40 with the socioeconomic status of the family in which a child is reared.

Question 114

How do educational experiences impact intelligence?

Answer 114

Many studies have shown that school attendance can raise IQ and that lack of attendance can lower it. A small decrease in IQ occurs over summer holidays, especially among low-income children. Intelligence quotient scores also drop when children are unable to start school on time owing to teacher shortages or strikes, natural disasters, or other reasons. It appears that exposure to an environment in which children have the opportunity to practise mental skills is important in solidifying those skills.

Question 115

Is personality heritable?

Answer 115

Behavioural genetics studies on personality have examined genetic and environmental influences on relatively broad personality traits.

Question 116

What is the five factor model?

Answer 116

One prominent personality trait theory is called the five factor model. Five factor theorists believe that individual differences in personality can be accounted for by variation along five broad personality dimensions or traits known as the Big Five:

(1) extraversion-introversion (sociable, outgoing, adventuresome, spontaneous versus aloof, quiet, inhibited, solitary)
(2) agreeableness (cooperative, helpful, good natured versus antagonistic, uncooperative, suspicious)
(3) conscientiousness (responsible, goal-directed, dependable versus undependable, careless, irresponsible)
(4) neuroticism (worrying, anxious, emotionally unstable versus well adjusted, secure, calm)
(5) openness to experience (imaginative, artistically sensitive, refined versus unreflective, crude and boorish, lacking in intellectual curiosity)

Question 117

What results are obtained if we compare the Big Five traits in identical and fraternal twins who were raised together and those who were raised apart?

Answer 117

Results show that heritability estimates of the Big Five personality factors are consistent with studies of other personality variables as well, indicating that between 40 and 50% of the personality variations among people included in these studies are attributable to genotype differences. Although personality characteristics do not show as high a level of heritability as the .70 figure found for intelligence, it is clear that genetic factors account for a significant amount of personality difference.

Question 118

How does environment influence personality?

Answer 118

If genetic differences in previous twin studies account for only about 40 to 50% of variations in personality, then surely environment is important too. The assumption has been accepted that experiences within the family, such as the amount of love expressed by parents and other child-rearing practices, are critical determinants of personality development.

Question 119

What has been found regarding major personality traits and the environment?

Answer 119

One study found that shared features of the family environment account for little or no variance in major personality traits. The key findings was that twins raised together ad apart, whether identical or fraternal, did not differ in their degree of personality similarity (although identical twins were always more similar to one another than were fraternal twins). In fact, researchers have found that pairs of children who are raised within the same family are as different from one another as are pairs of children who were randomly selected from the population

Question 120

What do adoption studies show regarding personality and the environment?

Answer 120

In adoption studies, the average correlation for personality variables between adopted siblings who are genetically dissimilar but do share much of their environment, including the parents who raise them , the schools they attend, the religious training they receive, and so on, is close to .001. Except at child-rearing extremes, where children are abused or seriously neglected, parents probably get more credit when children turn out well personality-wise - and more blame when they do not - than they deserve

Question 121

Despite findings suggesting that environment is not as important in impacting personality as was once thought, how can it still be important?

Answer 121

Rather than the general family environment, it seems to be the individual’s unique or unshared environment, such as his/her unique school experiences and interaction with specific peers that account for considerable personality variance. Even within the same family, we should realise, siblings have different experiences when growing up, and each child’s relationship with his/her parents and siblings will vary. It is these unique experiences that help shape personality development.

Question 122

What have behavioural geneticists found shared environment to affect and not affect?

Answer 122

They have found important shared environment effects in intelligence, attitudes, religious beliefs, occupational preferences, notions of masculinity and femininity, political attitudes, and health behaviours such as smoking and drinking, these shared-environment effects do not extend to general personality traits such as the Big Five. At this point, we do not know whether there are some crucial unshared-environmental variables that researchers have missed because of their preoccupation with shared-environmental factors, or whether there are countless small variables that make the difference.

Question 123

What is key to remember about genes and the environment and their influence?

Answer 123

They rarely operate independently. Even the prenatal environment can influence how genes express themselves, as when the mother’s drug use or malnutrition retards gene-directed brain development. In the critical periods following birth, enriched environments, including the simple touching or massaging of newborns, can influence the unfolding development of premature infants and the future ‘personality’ of young monkeys. Although they cannot modify the genotype itself, environmental conditions can influence how genetically based characteristics express themselves phenotypically throughout the course of development

Question 124

What does reaction range mean?

Answer 124

The range of possibilities - the upper and lower limits - that the genetic code allows
For example, to say that intelligence is genetically influenced does not mean that intelligence is fixed at birth. Instead, it means that an individual inherits a range for potential intelligence that has upper and lower limits. Environmental effects will then determine where the person falls within these genetically determined boundaries.

Question 125

How has the concept of reaction ranges mostly been applied?

Answer 125

At present, genetic reaction ranges cannot be measured directly, and we do not know if their sizes differ from one person to another. The concept has been applied most often in the study of intelligence. There, studies of IQ gains associated with environmental enrichment and adoption programmes suggest that the ranges could be as large as 15 to 20 points on the IQ scale. If this is the case then the influence of environmental factors on intelligence would e highly significant. A shift this large can move an individual from a below-average to an average intellectual level, or from an average IQ that would not predict college success to an above-average one that would predict success

Question 126

What does intellectual growth depend upon?

Answer 126

It depends on not only on genetic endowment and environmental advantage, but also on interests, motivation and other personal characteristics that affect how much we apply ourselves or take advantage of our gifts and opportunities

Question 127

How do heritability estimates vary?

Answer 127

Heritability estimates are not universal by any means. They can vary, depending on the sample being studied, and they may be influenced by environmental factors.

Question 128

What is thought to be likely about genetically based reaction ranges for personality factors?

Answer 128

That there are genetically based reaction ranges for personality factors too. This would mean that, personality-wise, there are biological limits to how malleable, or changeable, a person is in response to environmental factors. However, this hardly means that biology is destiny. Depending on the size of reaction ranges for particular personality characteristics - an even, perhaps, for different people - individuals could be quite susceptible to the impact of unshared environmental experiences.

Question 129

How do genetically based characteristics influence aspects of the environment to which the child is exposed?

Answer 129

For example, we know that intelligence has strong heritability. Thus, a child born to highly intelligent parents is also likely to have good intellectual potential. If, because of their own interests in intellectual pursuits, these parents provide an intellectually stimulating environment with lots of books, educational toys, computers and so on, this environment may help foster the development of mental skills that fall at the top of the child’s reaction range. The resulting bright child is thus a product both of the genes shared with the parents and of his or her ability to profit from the environment they provide.

Question 130

What is evocative influence?

Answer 130

A child’s genetically influenced behaviours may evoke certain responses from others

Question 131

Give an example of evocative influence —

Answer 131

For example, some children are very cuddly, sociable and outgoing almost from birth, whereas others are more aloof, shy and do not like to be touched or approached. These characteristics are, in part, genetically based. The outgoing children are likely to be cuddled by their parents and evoke lots of friendly responses from others as they mature, creating an environment that supports and strengthens their sociable and extraverted tendencies. In contrast, shy, aloof children typically evoke less positive reactions from others, and this self-created environment may strengthen their genotypically influenced tendency to withdraw from social contact

Question 132

In what 3 ways can genetic and environmental factors interact with one another?

Answer 132

• Reaction range
• Genetically based characteristics influencing aspects of the environment
• evocative influence

Question 133

What can behaviour patterns do to an environment?

Answer 133

Create an environment that counteracts the genetically favoured trait and discourages its expression. We know, for example, that activity level has moderate heritability of around .40. Thus, parents of highly active ‘off the wall’ children may try to get them to sit still and calm down, or those of inactive children may press the child into lots of physical activities designed to increase physical well-being, in both instances opposing the natural tendencies of the children. Thus, the environment may either support or discourage the expression of a person’s genotype

Question 134

How do people actively seek out environment and avoid others?

Answer 134

Genetically based traits may affect the environments that we select, and these environments are likely to be compatible with our traits. Thus, a large, aggressive boy may be attracted to competitive sports with lots physical contact, a highly intelligent child may shun social events and prefer solitary activities or a small number of friends. These varied self-selected environments may have very different effects on subsequent development. We therefore see that how people develop is influenced by both biology and experience, and that these factors combine in ways that are just beginning to be understood.

Question 135

What is epigenetics?

Answer 135

Epigenetics is the study in gene expression due to environmental factors and independent of the DNA
OR
‘alterations in the phenotype or gene expression due to mechanisms other than changes in the underlying DNA sequence’

Question 136

What does the area of epigenetics research open up?

Answer 136

A new area where, not content with looking at naturally occurring genetic phenomena, scientists can now directly influence, manipulate and duplicate the structure of genes themselves. Of course, natural expressions and manipulations have been carried out for centuries, notably by Mendel and animal breeders, but epigenetics opens up a door to an as yet unthinkable level of flexibility regarding genetic expressions

Question 137

What is important in gene expression?

Answer 137

It is not only the DNA itself that is vital in the expression of the gene. Researches say that the physical environment in which the genes resides, as well as the social environment of the host, can be influential in changing molecular structures that are themselves responsible for regulating gene expression

Question 138

How can gene manipulation be achieved?

Answer 138

Therapies can be developed to modify the structure of brain tissue. To do this, you first need to find a virus that can travel into the brain. Next you need to modify the genetic code of the virus before it is released into the host. Enzymes are used that can split threads of the DNA to be inserted into pieces before, before combining it with the DNA of the virus, which then carries the inserted DNA to the brain. Similarly, the DNA of bacterium can be modified with pieces of DNA so that when inserted into a host, the new bacterium subdivides to produce multiple copies of itself, spreading the DNA throughout the host

Question 139

What are the 2 types of genetic modification?

Answer 139

Knock-out procedures and knock-in procedures

Question 140

What is a knock-out procedure?

Answer 140

Where a function of a gene is removed, or eliminated

Question 141

What is a knock-in procedure?

Answer 141

Where a new gene is inserted into an animal at embryonic stage

Question 142

What are the potential benefits of genetic screening?

Answer 142

There are at present more than 900 genetic tests available from testing laboratories. Proponents argue that screening can provide information that will benefit people. Early detection of a treatable condition can save lives. Screening could also affect reproductive decisions that reduce the probability of having children affected by a genetic disease.

Question 143

How accurate is genetic screening?

Answer 143

Although screens for various diseases exceed 90% accuracy, it is still possible that there can be a false positive result (an indication that genetic predisposition to a disorder is present when it is not). Thus, a person may decide not to have children on the basis of an erroneous test that indicates a high risk of having a child with a particular problem. Alternatively a false negative test may indicate that a predisposition is not present when in fact it is. Moreover, some tests, called susceptibility tests, simply tell you that you are more likely than others to develop a particular disorder, with no assurance that that will indeed occur

Question 144

How should people be educated and counselled about test results?

Answer 144

Because of the importance of decisions that might be made on the basis of genetic screening, there is strong agreement that clients should be educated and counselled by specially trained counsellors. In the sickle-cell anaemia screening of the 1970s, follow-up education was inadequate, the result being that some African-American men who were informed that they were carriers of the sickle-cell allele elected to remain childless because they were not told that the disorder would not occur in their offspring if their mated were noncarriers of the allele. The genetic counsellor’s role is to help the person, couple or family to decide whether to be screened, to help them to fully understand the meaning of the test results, and to assist them during what might well be a difficult and traumatic time

Question 145

How can evolution and human nature be connected?

Answer 145

The evidence from behavioural genetics has gone a long way to convincing people that human nature is indeed influenced by evolved predispositions. However, the application of principles of natural selection to psychology has not been without controversy. Indeed a healthy scepticism is to be recommended. There is a great danger in the misapplication of Darwin’s thinking.

Question 146

What danger can the application of evolutionary thinking pose?

Answer 146

Francis Galton argued that certain traits which might have been functional and useful in the past were not so in modern Victorian England. He coined the term ‘eugenics’ to describe a practice of improving the human race by encouraging the ‘desirable’ human traits through selective breeding. Those who had these ‘desirable’ traits should be encouraged to have children; those who did not (such as criminals) should be discouraged or prevented. Bitter experience has taught us that the principles of eugenics can be taken even further with horrifying consequences (e.g. Nazi Germany)

Question 147

What are adaptations?

Answer 147

Physical or behavioural changes that allow organisms to meet recurring environmental challenges to their survival, thereby increasing their reproductive ability

Question 148

What does eugenics do?

Answer 148

Eugenics placed an unmerited moral value on evolutionary adaptations. There is no ‘should’ or ‘ought’ in evolution - life just is the way it is.

Question 149

What can the process of evolution be described as?

Answer 149

A mechanical, purposeless process. It is not directed toward any particular higher goal or value. It is based upon random genetic mutations. The name of the game is long-term genetic survival and there is no particular moral merit in that. Thus, one should not consider any particular extant species evolutionary more worthy or advanced than any other.

Question 150

Why have eugenicists misunderstood the principles of evolution?

Answer 150

By placing value judgements onto natural selection, eugenicists fundamentally misunderstood the logic of the principles underlying Darwinian evolution as not in all circumstances is one gene preferable over another.

Question 151

What did Darwin propose about natural selection?

Answer 151

The origin of the species argued that natural selection does not work for the ‘good of the species’ or ‘the good of the group’. Instead, he proposed that natural selection would always favour biological traits that promoted the reproductive success of individuals over and above what is good for the group or species.

Question 152

What does biological fitness refer to?

Answer 152

Biological ‘fitness’ does not necessarily refer to the strongest or fastest or even longest-lived members of a population. If an organism lived or a thousand years, but died without doing anything to ensure that some biological part of it survived after its death, it would be an evolutionary dead end.
Darwin measured fitness in terms of the number of offspring an individual produces. However, we now know that the unit of inheritance is the gene. Thus, modern evolutionary theorists measure reproductive success in terms of the estimated number of copies of individual genes that survive into future generations

Question 153

What is kin selection?

Answer 153

An evolutionary strategy in which behaviours are selected which favour the reproductive success of an organism’s relatives even if that is at a cost to that organism’s our survival and reproduction

Question 154

Give examples of kin selection —

Answer 154

Lots of examples in nature of animals risking or even sacrificing their lives in order to protect their kin and the genes they carry. Thus, the world created by natural selection is not as entirely dog-eat-dog as one might suppose

Question 155

What is reciprocal altruism?

Answer 155

a behaviour in an organism which reduces its fitness to survive and reproduce while increasing another organism’s fitness, undertaken with the expectation that the favour will be returned later

Question 156

What are culturally universal characteristics?

Answer 156

If nearly every human culture, even those that are relatively isolated from all other human groups, expresses a certain characteristic it suggests the expression of inborn biological tendencies that have evolved through natural selection. There exists a vast catalogue of human culturally universal characteristics and capabilities that unfold in all normally developing human beings.

Question 157

Give some examples of culturally universal characteristics —

Answer 157

1) Infants are born with an ability to acquire any language spoken in the world
2) Human newborns are pre-wired to perceive specific stimuli e.g. human faces and mothers milk
3) At one week of age (babies less than 1 month), human neonates show primitive mathematical skills, successfully discriminating between 2 and 3 objects
4) Humans seem to have a need to belong and strongly fear being ostracised from the group
5) Possession of a basic set of emotions
6) in virtually all cultures, males are more violent and more likely to kill others

Question 158

How do men and women display different attitudes towards mating strategies and preferences?

Answer 158

Compared with women, men typically show more interest in short-term mating, prefer a greater number of short-term sexual partners, and have more permissive sexual attitudes and more sexual partners over their lifetime.

Question 159

How do men and women display different behaviours in mating strategies and preferences?

Answer 159

Findings of a research study in mating behaviour suggest that, women tended to react negatively to seeing a member of the opposite sex and being asked to go to bed with them that night, and usually dismissed the research assistant as ‘sleazy’. Not a single woman agreed to have sex. In contrast, 3 in every 4 men enthusiastically agreed, some asking why it was necessary to have to wait until that night.
Other findings show that men think about sex about 3x more than women do, desire more frequent sex and initiate more sexual encounters than women do.
Men are also much more likely to interpret a woman’s friendliness as a sexual come-on, apparently projecting their own sexual desires onto the woman

Question 160

What are the sex differences in mate selection?

Answer 160

Men typically prefer women somewhat younger than themselves, whereas women prefer somewhat older men. This tendency is exaggerated in the ‘trophy wives’ sometimes exhibited by wealthy and famous older men.
In mate preferences in terms of personal traits across 37 cultures, men and women show considerable overall agreement, but some differences emerge. Men place greater value on a potential mate’s physical attractiveness, whereas women place greater value on a potential mate’s earning potential, status and ambitiousness

Question 161

What is the viewpoint of the sexual strategies theory (and a related model) and the parental investment theory?

Answer 161

Mating strategies and preferences reflect inherited tendencies, shaped over the ages in response to different types of adaptive problems that men and women faced.
In evolutionary terms, our most successful ancestors were those who survived and passed down the greatest number of their genes to future generations. Men who had sex with more partners increased the likelihood of fathering more children so they were interested in mating widely. Men may also have taken a woman’s youth and attractive, healthy appearance as signs that she was fertile and had many years left to bear his children.

Question 162

What evolutionary reasoning is there behind female mating behaviours?

Answer 162

Ancestral women had little to gain and much to lose by mating with numerous men. They were interested in mating wisely, not widely. In humans and other mammals, females typically make a greater investment than males: they carry the foetus, incur health risks and possible birth-related death, and nourish the newborn. Engaging in short-term sexual relationships with multiple males can in the end create uncertainty about who is the father, thereby decreasing a male’s willingness to commit resources to helping a mother raise the child. For these reasons women maximized their reproductive success - and the survival chances of themselves and their offspring - by being selective and choosing mates who were willing and able to commit time, energy and other resources to the family. Women increased their likelihood of passing their genes into the future by mating wisely, and men by mating widely. Due to natural selection, it has been suggested that these preferences have become part of their biological nature

Question 163

Why could these mate preferences be more pronounced in different parts of the world?

Answer 163

Some of these mate preference patterns are ore pronounced in parts of the world with historically high levels of pathogens that endangered survival than in areas that had historically low levels of pathogens. Where diseases like malaria, plague and yellow-fever are more prevalent, male factors such as physical attractiveness and robustness, intelligence and social dominance - all presumably signs of biological fitness - seem especially important to women even today. It has been suggested that in such environments, women seem willing to sacrifice some degree of male investment in their offspring in favour of a mate who has a higher probability of giving them healthy children. To men, a woman’s attractiveness and healthiness (and that of her family) also is more important in high-pathogen environments, presumably because these historically were signs of a woman who would be more likely to give birth to healthy children and live long enough to rear them

Question 164

What is the social structure theory?

Answer 164

Men and women display different mating preferences not because nature impels them to do so, but because society guides them into different social roles

Question 165

How does the social structure theory suggest that adaptive behaviour patterns have been passed on?

Answer 165

Passed on from parents to children not through genes but through learning. Social structure theorists point out that despite the shift in the past several decades towards greater gender equality, today’s women still have generally less power, lower wages and less access to resources than men do. In a two-income marriage, the woman Is more likely to be the partner who switches to part-time work or becomes a full-time homemaker after childbirth. Thus, society’s division of labour still tends to socialize men into the breadwinner role and women into the homemaker role.

Question 166

What is the division-of-labour hypothesis?

Answer 166

Given the power and resource disparities and the need to care for children, it makes sense for women to seek men who will be successful wage earners and for men to seek women who can have children and fulfil the domestic-worker role. An older male-younger female age gap is favourable because older men are likely to be further along in earning power and younger women are more economically dependent, and this state of affairs conforms to cultural expectations of marital roles. This hypothesis does not directly address why men emphasize a mate’s physical attractiveness more than women do but it has been speculated by Alice Eagley and Wendy Wood (1999)that attractiveness is viewed as part of what women ‘exchange’ in return for a male’s earning capacity

Question 167

What are the two competing explanations for sex differences in mating behaviour?

Answer 167

The evolution-based sexual strategies approach and the social structure view

Question 168

What is the evolutionary personality theory?

Answer 168

An approach which looks for the origin of presumably universal personality traits in the adaptive demands of our species’ evolutionary theory

Question 169

What does the evolutionary personality theory pose?

Answer 169

It asks the basic question, ‘where did the personality traits exhibited by humans come from in the first place?’ The focus here is on the traits that we (and other animals)have in common. But evolutionary personality theory also tries to account for the core question in the field of personality: why do we differ from one another in the personality traits?

Question 170

How does the five factor model of personality link to evolution?

Answer 170

Because these 5 trait dimensions - extraversion, agreeableness, conscientiousness neuroticism and openness to experience - have been found in people’s descriptions of themselves and others in virtually all cultures, some theorists regard them as universal among humans. And because evolutionary theory addresses human universals, the Big Five traits have been the major focus of evolutionary personality theory

Question 171

Why are the Big Five traits found so consistently in the languages nd behaviours in cultures around the world?

Answer 171

According to Buss (1999), they exist in humans because they have helped us achieve two overriding goals: physical survival and reproductive success. Traits such as extraversion and emotional stability would have been helpful in attaining positions of dominance and mate selection. Conscientiousness and agreeableness are important in reproduction and the care of children, Finally, openness to experience may be the basis for problem-solving and creative activities that benefit not only the possessor but also are likely to be valued by other group members. Rewarding and encouraging these traits could be to the mutual benefit of everyone. Evolutionary theorists therefore regard the behaviours underlying the Big Five as sculpted by natural selection

Question 172

How can the Big Five traits be linked with how we are biologically programmed to think about and discriminate among people? (5 Questions)

Answer 172

Goldberg (1981) suggests that over the course of evolution, people have had to ask some very basic questions when interacting with another person, questions that have survival and reproductive implications:
1) Is person X active and dominant or passive and submissive? Can I dominate X, or will I have to submit to X?
2) Is X agreeable and friendly or hostile and uncooperative?
3) Can I count on X? Is X consciousness and dependable?
4) Is X sane (stable, rational, predictable) or crazy (unstable, unpredictable, possibly dangerous)?
5) How smart is X, and how quickly can X learn and adapt?
Not surprisingly, Goldberg suggests that these questions relate directly to the Big Five factors. He believes that this is the reason analyses of trait ratings reveal Big Five consistency across very diverse cultures.

Question 173

What is strategic pluralism?

Answer 173

The idea that multiple - even contradictory - behavioural strategies might be adaptive in certain environments and would therefore be maintained through natural selection

Question 174

Why do we see variation in the Big Five traits?

Answer 174

Thus, Daniel Nettle (2006) theorizes that we see variation in the Big Five traits because all of them have adaptive trade-offs (a balance of potential benefits and costs) in the outcomes they may produce
Nettle believes that these trade-offs favour evolutionary variation in the Big Five traits and that the specific environment in which our ancestors evolved made it more or less adaptive to be an extravert or an introvert, agreeable or selfish, fearful or fearless, conscientious or immoral, and so on. This would help account for genes favouring individual differences on personality dimensions and for the great diversity we see in personality trait patterns

Question 175

How do evolutionary psychologists account for individual differences in personality traits through gene-environment interactions?

Answer 175

Evolution may provide humans with species-typical behaviour patterns, but environmental inputs influence how they are manifested. For example, dominance may be the behaviour pattern encouraged by innate mechanisms in males, but an individual male who has many early experiences of being subdued or dominated may develop a submissive personality