Genetics and evolutionary foundations of behaviour - a summary of chapter 3 of Psychology by Gray and Bjorklund (7th edition)

Psychology
Chapter 3
Genetics and evolutionary foundations of behaviour

Review of basic genetic mechanisms

Adaption refers to modifications as a result of changed life circumstances.
Evolution is a long-term adaptive process.

How genes affect behavior

Genes are associated with behavior (they never produce or control behavior directly).
All the effects that genes have on behavior occur through their role in building and modifying the physical structures of the body. Those structures, interacting with the environment, produce behavior.
All genes that contribute to the body’s development are “for” behavior. Since all parts of the body are involved in behavior.

Genes provide the codes for proteins

Genes affect the body’s development (only) through their influence on the production of protein molecules.

Structural proteins; forms the structure of every cell of the body.
Enzymes; controls the rate of every chemical reaction in every cell.

Genes are components of extremely long molecules of a substance called DNA (deoxyribonucleic acid).
These molecules exist in the egg and sperm cells that join to from a new individual. And they replicate themselves during each cell division in the course of the body’s growth and development.
A replica of your whole DNA molecules exists in the nucleus of each of your body’s cells, where it serves to code for and regulate the production of protein molecules.

Each protein molecule consists of a long chain of smaller molecules. Those are amino acids.
A single protein molecule may contain from several hundred to many thousand amino acids in its chain.
There are a total of 20 distinct amino acids in every from of life on earth (and they can be arranged in countless sequences to from different protein molecules).
Some DNA serve as templates (as molds or patterns) for producing RNA. RNA severs as a template for producing protein molecules.

A gene is segment of a DNA molecule that contains the code that dictates the particular sequence of amino acids for a single type of protein.
A human being has between 20.000 and 25.000 genes.
Most of the DNA in human cells does not code for proteins.

• Coding genes; code for unique protein molecules
• Regulatory genes; work through various biological means to help activate or suppress specific coding genes and thereby influence the body’s development.

Genes work only through interaction with the environment

The effects of genes are entwined with the effects of the environment.
Environment; every aspect of an individual and his or her surroundings except the genes themselves. (Everything! Even the internal chemical environment of the individual)
Environmental effects also help to turn genes ‘on’ and ‘off’ resulting in bodily changes that alter the individual’s behavioral capacity (always happens, in childhood and adulthood).

One’s body and behavioral capacities result from a continuous, complex interplay between genes and environment.
Genes are always expressed in a context!
Experience activates genes, which produce proteins, which alter the function of some of the neural circuits in the brain and thereby change the manner in which the individual behaves.

Distinction between genotype and phenotype

• Genotype: the set of genes that the individual inherits.
• Phenotype: the observable properties of the body and behavioral traits.

The same gene can have different effects, depending on the environment and the mix of other genes.
Two individuals with the same genotype can be different in phenotype as a result of differences in their environments.

How genes are passed along in sexual reproduction

Genes do provide codes for building proteins,
And they serve as the biological units of heredity

Genes are replicated and passed along from parents to offspring. They are the cause of offspring’s’ resemblance to parents. 

Genetic material (DNA) exists in each cell in structures called chromosomes. Those are usually dispersed throughout the cell nucleus (kern).
The normal human cell has 23 pairs of chromosomes.
22 of these pairs are true pairs in both male and female (each chromosome looks like its mate and contains similar genes). The remaining pair is made up of the sex chromosomes. XX is female and XY is male.

Production of genetically diverse egg and sperm cells

Mitosis; the process when cells divide to produce new cells other than egg or sperm cells.
Each chromosome precisely replicates itself and then the cell divides (with one copy of each chromosome moving in each of the two cell nuclei thus formed.
Because of this, all body cells (except for egg and sperm cells) are genetically identical to another. The differences of cells in your body (skin and brain) arise from the differential activation in their genes.

Meiosis; the process when cells divide to produce egg or sperm cells.
In meiosis, the cells are not genetically alike.
During meiosis, each chromosome replicates itself once, but then the cell divides twice. Before this cell division, the chromosomes of each pair line up next to one another and exchange genetic material in a random manner. They do not contain precisely the same genes.

The genetic diversity of offspring

When a sperm and an egg cell untie, they from a new cell, the zygote (which contains the full complement of 23 paired chromosomes). One member of each pair comes from each parent.

The value of sex, lies in the production of genetically diverse offspring. In a changing world, genes have better chance of surviving if they are rearranged at each generation in many different ways (to produce different kinds of bodies). Parents reduce the chance of all the offspring dying by a change of the environment. 

Identical twins.
When two bundles of cells separate from each other during the early mitotic divisions following the formation of a zygote. (Monozygotic (good spelling) twins).

Fraternal twins
Dizygotic twins
Originate from two zygotes, each formed from different egg and sperm cells.

Consequences of the fact that genes come in pairs

Two genes that occupy the same locus (location) on a pair of chromosomes are sometimes identical and sometimes not.
When identical; the individual is homozygous at that locus.
Not identical; the individual is heterozygous at that locus.
Different genes that can occupy the same locus (and thus can potentially pair with each other) are called alleles.

A dominant gene (or allele); one that will produce its observable effects in either the homozygous or the heterozygous condition.
A recessive gene (or allele); one that will produce its effects in the homozygous condition only.
Some pairs of genes blends their effects.

Mendelian pattern of heredity

Gregor Mendel
Developed the idea that the units of heredity come in pairs and that one member of a pair can be dominant over the other.

The double-edged sword of sickle-cell anemia
Some genetic conditions (like sickle cell anemia) carry both risk and benefits for the individuals born with them.

The inheritance of behavioral traits

Variation in genes contributes to the variation in behavior
Some behavioral characteristics are inherited indicative of control by a single pair of genes.
Most behavioral characteristics depend on many genes.

Polygenic characteristics and selective breeding

Characteristics that derive from variation at a single gene locus are typically categorical in nature. (Those are characteristic that sharply differentiate one group from another).
Most anatomical and behavioral differences among individuals of any species are measurable in degree, not type. They are continuous (the measures taken from individuals do not fall into two or more distinct groups, but can lie anywhere within the observed range of scores). A normal distribution.

Polygenic characteristics; characteristics that vary in a continuous way and are generally affected by many genes. Of course these traits are also influenced by variation in the environment.

Selective breeding for behavioral characteristics in animals

To the degree that individuals within a species differ in any measurable characteristic because of differences in their genes, that characteristic can be modified by selective breeding.
For single-gene characteristics the effects of selective breeding are immediate
For polygenic characteristics the effects are gradual and cumulate over generations.

A few words about epigenetics

Genes are only part of the story.
Epigenetics examines gene-regulating activity that doesn’t involve changes to the DNA code and that can persist through one or more generations.
We inherit from our parents not only DNA, but also a variety of chemical markers that regulate genes (turning them on at certain times and off at others. And determining how much protein they produce).
Early experience can alter behavior and be transmitted to future generations (all without any changes in the genes themselves).

Evolution by natural selection

Darwin’s insight: selective breeding occurs in nature

Breeding in nature is selective and can produce changes in living things over generations.
Natural selection.
Is dictated by the obstacles to reproduction that are imposed by the natural environment (anything that prevent an organism from producing offspring). Organisms that have characteristics that help them overcome such obstacles are more likely to have offspring.

Four concepts of natural selection:

• There is overproduction of offspring
• There is variation in features or traits within members of a generation
• Individual differences are inherited from one generation to the next
• Individuals with collections of traits that fit well with the local environment are more apt to survive and have more offspring than individuals whose traits do not fit as well with the local environment.

Genetic diversity provides the material for natural selection

Darwin knew nothing about genes.

The genetic variability on which natural selection acts has two main sources:

• The reshuffling of genes that occurs in sexual reproduction
• Mutations

Mutations are errors that occasionally and unpredictably occur during DNA replication, causing the replica to be not identical to the original.
Mutation is the ultimate source of all genetic variation.
Occasionally a mutation is useful, producing a protein that affects the organism’s development in a way that increases its ability to reproduce. Because of its effects on reproduction, the gene arising from such a mutation increases in frequency from generation to generation. At the level of the gene, this is evolution.

Environmental change provides the force for natural selection

Evolution is spurred by changes in the environment.
Evolution can occur in speed depending on the rate and nature of environmental change and on the degree to which genetic variability already exists in a population.

Evolution has no foresight

Evolution has no foresight.
Evolution has no planned end no organism is ‘more evolved’.
Evolution has no moral force.

Natural selection as a foundation for functionalism

Functionalism: the attempt to explain behavior in terms of what it accomplishes for the behaving individual.

Distal and proximate explanations for behavior

Two kinds of explanations of behavioral. Both are needed to understand behavior.

• Distal
  Explanations on evolutionary level.
  Statements on the role that the behavior played in the animal’s survival and reproduction over evolutionary time. How did the ancestors genes make it to the next generation?
  (Ultimate causation)
• Proximate
  Deal with mechanism.
  Statements of the immediate conditions, both inside and outside the animal.

Distal and proximate explanations complement each other

Limitations on functionalist thinking

Four reasons why a particular trait or behavior may not be functionalism

Some traits are vestigial

Some traits that evolved because they served the needs of our ancestors are no longer functional today, yet they remain. → Vestigial characteristics.
This is relevant to psychologists when applied to our inherited drives or motives.

Some traits are side effects of natural selection for other traits

Useless changes can come about in evolution as by-products of natural selection for other useful changes.
(For example the belly button)
It is possible that some human capacities came about in side effects of the evolution of other capacities.

Some traits result simply from chance

Some inheritable characteristics that result from just one or two mutations are inconsequential for survival and reproduction.
(For example the shape of nose)
Genetic drift: trough chance alone

Evolved mechanisms cannot deal effectively with every situation

Even evolved mechanisms, like guild, are not useful in every situation in which they are active

Natural selection as a foundation for understanding species-typical behaviors

Species-typical behaviors in humans

Species-typical behavior are products of evolution, but they are influenced by learning.

Human emotional expressions as examples of species-typical behaviors

Specific facial expressions accompany specific emotional states in humans. Those are universal.
People can identify each emotion more easily and accurately when it is expressed by members of their own culture.

The role of learning in the development of species-typical behavior

The role of learning is obvious in our two most characteristic species-specific behaviors. Manner of walking and language.

Biological preparedness as the basis for species-typical behaviors

The difference between behaviors that we call species-typical and those we don’t has to do with their degree of biological preparedness.
Natural selection has equipped each species with anatomical structures that ensure that normal individuals of the species will be physical able to perform their species-typical behaviors and will be motivated to learn what they must for adequate performance.

Species-typical behavior is a relative concept

No behavior stems just from biological preparedness. Some sort of experience with the environment is always involved.
Any behavior that an individual can produce must make use of the individual’s inherited biological capacities.

The value of cross-species comparisons of species-typical behaviors

Two forms of cross-species comparison: Homologies and Analogies

A homology: any similarity that exits because of the different species common ancestry.
The more closely related two species are, the more homologies they show.

An Analogy: any similarity that stems from convergent evolution.
Convergent evolution occurs when different species (because of some similarity in their habitats or lifestyles) independently evolve a common characteristic.
(For example, groups of animals that can fly).

The value for psychology of studying homologies

Homologies are useful for research on the physiological mechanisms of behavior because convergent evolution can produce similar behavior that operate through different mechanisms.
Also useful for inferring the pathways along which species-typical behaviors evolved.

The value for psychology of studying analogies

Analogies are useful for making inferences about the distal functions of species-typical behavior.

Evolutionary analysis of mating patterns

Four mating classes

• Polygyny
  One male and more than one female
• Polyandry
  One female and more than one male
• Monogamy
  One female and one male
• Promiscuity
  Members of a group consisting of more than one male and more than one female mate with another

(poly = many, mono = one, gyn = female, andr = male)

A theory relating mating patterns to parental investment

Robert Trivers (1972)

A theory relating courtship and mating patterns to sex differences in amount of parental investment.
Parental investment is the time, energy and risk to survival that are involved in producing, feeding and otherwise caring for each offspring.

In general, for species in which parental investment is unequal, the more parentally invested sex will be a) more vigorously competed for than the other and b) more discriminating than the other when choosing mates.

Polygyny is related to high female and low male parental investment

When the evolutionary advantage in mating with multiple partners is greater for males, than for females, a pattern evolves in which males complete with one another to mate with as many females as they can.
The more polygynous a species, the greater is the average size difference between males and females.

Polyandry is related to high male and low female parental investment

Mostly by birds and fish.
Once the eggs are laid, they can be cared for by either parent. Depending on other conditions, evolution can lead to greater male than female parental investment.

Monogamy is related to equivalent male and female parental investment

When the two sexes make approximately equal investments in their young, their degree of competition for mates will also be approximately equal. Monogamy will prevail.
This is most likely to come about when conditions make it impossible for a single adult to raise the young, but quite possible for two to raise them.
Social monogamy does not necessarily imply sexual monogamy.

Promiscuity is related to investment in the group

Because any male in the colony could be the father, each male’s evolutionary interest lies not in attacking the young but helping to protect and care for the group as a whole.

What about human mating patterns?

Largely monogamous, partly polygynous species

Humans fall on the boundary between monogamy and polygyny.
Another clue to Homo sapiens prehistorically patterns comes from a comparative analysis of different types of white blood cells.
The more sexual partners a one has, the stronger one’s immune system needs to be to combat infection. The human immune system is between polygynous and monogamous.

The role of emotions in human mating systems

Our biological equipment that predisposes us for mating bonds includes brain mechanisms that promote the twin emotions of romantic love and sexual jealousy. Those are found in every culture that has been studied.
Love tends to create mating bonds, jealousy tends to preserve such bonds by motivating each member of a mated pair to act in ways designed to prevent the other from having an affair with someone else.
Other animals that form long-termed mating bonds show evidence of emotions that are functionally similar to human love and jealousy. 
Lust tends to motivates to engage surreptitiously in sex outside of such bonds.
A woman who has sex with men other than her husband may benefit evolutionary:

• Increase her chances of conception
• Increase the evolutionary fitness of her offspring if the genes are superior over those of her husband.
• Result in provisions from more than one man

Evolutionary analyses of hurting and helping

Human beings, like other animals, are motivated both to hurt and help one another in the struggle to survive and reproduce.
Completion is the foundation for aggression.

Sex differences in aggression

Aggression a behavior intended to harm another member of the same species.
Brain mechanisms that motivate and organize such behavior are evolved because they help animals acquire and retain resources needed to survive and reproduce.

Polygynous males and polyandrous females fight over mates. Monogamous males fight to prevent other males from copulating with their mates (and the other way around). Promiscuous females fight to keep immigrating females from competing for resources.

Why male primates are generally more violent than female primates

Male primates are more likely to maim or kill their opponents.

Most of the violence perpetrated by male primates has to do directly or indirectly with sex.

• Male apes have been observed to kill infants fathered by others to get the females to stop lactating so they will ovulate again
• Males fight with another to gain access to a particular female or to rise their rank in the dominance hierarchy
• Violent towards females to force copulation or to prevent copulation with other males

The female at battle risks not only her life, but also that of any fetus she is gestating or young she is nursing

Male violence in humans

Humans are no exception to the usual primate rule.
Men are more violent.

Patterns of helping

Helping is any behavior that increases the survival chance or reproductive capacity of another individual.

Two forms:

• Cooperation
  When an individual helps another while helping itself.
  Working with others for common ends, each individual has a better chance of survival and reproduction than it would have alone.
• Altruism
  When an individual helps another while decreasing its own chance of survival or reproductive capacity.
  Less common.

Two theories of altruism:

The kin selection theory of altruism

Behavior that seems to be altruistic came about through natural selection because it preferentially helps close relatives, who are genetically most similar to the helper.
What actually survives over evolutionary time is not the individual but the individual’s genes.
Any gene that promotes the production and preservation of copies of itself can be a fit gene, from the vantage point of natural selection, even if it reduces the survival chances of a particular carrier of the gene.

Animals help kin more than nonkin.

The reciprocity theory of apparent altruism

The reciprocity theory provides an account of how acts of apparent altruism can arise even among nonkin.
Behavior seems to be altruistic are actually forms of long-term cooperation.
Genetically induced tendency to help nonkin can evolve if:

• There is an ability to remember which individuals have reciprocated such help in the past
• There is a tendency to refrain from helping again those who failed to reciprocate previous help.
  Under this conditions, helping is selfish because it increases the chances receiving help from that other in the future.

Final words of caution: two fallacies to avoid

1 Natural selection is not a moral force

2 Our genes do not control our behavior in ways that are independent of the environment

The naturalistic fallacy

The equation of natural, with moral or right.
Such equations are logically indefensible because nature itself is neither moral nor immoral except as judged by us.

Deterministic fallacy

The assumption that genetic influences on our behavior take the form of genetic control of our behavior, which we can do nothing about.
This mistake is assuming or implying that genes influence behavior directly rather than through the indirect means of working with the environment to build or modify biological structures that then, in interplay with the environment, produce behavior.
We humans can control our environment and therefor ourselves.