Chapter 3
Genetic and Evolutionary Foundations of Behavior

Outline Misconceptions About Evolution
Genes and the Inheritance of Behavioral Characteristics
Natural Selection and Its Implications for Psychology
Ethology: The Study of Species-Typical Behavior Patterns
Sociobiology: The Comparative Study of Animals' Social Systems

Misconceptions About Evolution

"Nothing will ever be attempted if all possible objections must first be overcome"

- Samuel Johnson quoted in: Dugatkin, L. (1999). Cheating monkeys and citizen bees. New York: The Free Press).

Example: True or False?

"Species can be arranged on an evolutionary ladder from bacteria through 'lower' animals, to "higher" animals and, finally, up to man."

Example: True or False?

Evolution can be equated with progress. Through evolution, populations become better. The traits and strategies that evolve necessarily make them more successful.

LINK: The Darwin Awards

DNA

Genes and The Inheritance of Behavioral Characteristics

Characteristics that are inherited biologically do so through genes. A gene is defined as a segment of a DNA molecule that contains the code for manufacturing a specific type of protein molecule.

Genes affect behavior by building and modifying physical structures of an organism. Those structures then interact with the environment, producing behavior.

Protein molecules - Becuase our bodies are made up of several thousand of these molecules, protein molecules make us what we are. Structural proteins form our cell structures and enzymes control the rate of chemical reactions in cells.

Genes - Genes are biological units of heredity. They are replicated and passed from parent to offspring and they are crucial to the development of each new individual. Characteristics that are inherited biologically are inherited through genes.

Genotype - These are all the genes that an individual inherits.

Phenotype - These are the observable properties of the body an behavioral traits.

How genes are passed along in sexual reproduction

Chromosomes - This is the genetic material that exists in the nucleus of each cell.

Mitosis - This is when cells other than egg or sperm cells divide to produce new cells.

Meiosis - This is the process by which when sperm or egg cells divide to produce new cells.

Zygote - The new, single cell that results from an egg and sperm cell uniting.

Identical twins (monozygotic) - These are twins that are genetically identical.

Fraternal twins (dizygotic) - These twins originated from two zygotes, formed when two different eggs are each joined by a different sperm.

Consequences that genes come in pairs

Locus - This is simply the location of a gene on a chromosome.

Homozygous - When the two genes that occupy the same locus on a pair off chromosomes are identical, the individual is said to be homozygous at that locus.

Heterozygous - When the two genes that occupy the same locus on a pair off chromosomes are NOT identical, the individual is said to be heterozygous at that locus.

Alleles - Different genes that can occupy the same locus, and thus can potentially pair with one another, are referred to as alleles.

Dominant genes - This is a gene (or allele) that will produce its observable effects in either the homozygous or heterozygous condition.

Recessive genes - These genes (or alleles) are those that will produce its effects if ONLY in the homozygous condition.

Mendelian Patterns of Heredity

Gregor Mendel - Mendel was a monk and abbot, who experimented with the heredity of plants in his monastary's garden.

Mendel's 3:1 ratio - Mendel discovered that when two pea plants that are heterozygous for round versus wrinkled seeds are crossbred, four possible gene combinations occur. In three cases the phenotype of the offspring will be round, and in one case wrinkled. This 3:1 ratio was Mendel's famous finding.

Polygenic Characteristics and Selective Breeding

Normal distribution - Many of the characteristics measured in the social sciences approximate a normal distribution. This means that most scores obtained on a measure, such as height, fall near the middle of the range and the frequency of the scores tapers off in either direction.

Polygenic characteristics - These are characteristics that vary in a continuous way and are generally affected by many genes.

Mendel's 3:1 ratio

LINK: Pea Soup. The Story of Gregor Mendel.

Natural Selection and its Implications for Psychology

Charles Darwin and Natural Selection

Natural selection is another mechanism producing changes in the gene pool.

Charles Darwin: Suggested that natural selection is major mechanism through which evolution occurs.

Darwin proposed this as the mechanism, even though he didn't explain natural selection in terms of genetic change (Good understanding of genes didn't start until around 1900).

Natural selection involves the roadblocks that prevent some and encourage others to reproduce. Many roadblocks involve environmental changes (e.g., ice ages); some of environmental changes are, in part, produced by us (e.g., El Niño).

Modern understanding of Evolution

If we were all clones (genetically identical), would evolution take place?

Nope. Genetic variability is required.

Two sources of genetic variation:

(1) Reshuffling of genes through sexual reproduction

Reshuffling = Recombination = creation of new combinations of alleles.

Recombination is a mechanism of evolution because it adds new alleles and combinations of alleles to the gene pool.

(2) Mutations

Sometimes cellular machinery involved in copying DNA "makes" mistakes. The mistakes alter the sequence of the gene. This is called a mutation. Mutations increase genetic variability.

Many kinds of mutations

Many mutations are harmful. Some are helpful. Harmful how? Helpful how?

Don't confuse "survival of fittest" with natural selection. The phrase "survival of the fittest" is misleading. Survival is one aspect of selection. More important is mating.

Fit is often equated with physically fit (e.g., bigger, stronger, faster). But, in evolutionary terms, fit really means: "average reproductive output of a class of genetic variants in a gene pool." Translated: Whatever works to increase chances of passing along genes!

Moth example of natural selection (Kettlewell)

Prior to 1848, dark moths consisted of less than 2% of population around industrialized areas.

By 1898, 95% of moths in these areas were dark! Not true in more rural areas.

Why? Through process of natural selection

Industrial areas highly sooty, darkening normally light-colored birch trees on which moths landed

1848 - 1898: Birds ate light colored moths (easily visible prey). Less likely to eat dark moths. These survived and reproduced (passing on their gene pool).

Evolution has no foresight

There is no predetermined goal or end in the process of evolution; evolution has no foresight. Only those genetic changes that increase the liklihood of survival and reproduction in the current environment proliferate through natural selection.

Thinking about behavior in terms of its functions

Ultimate explanations:

Function that characteristic serves in enhancing survival or reproductive success. (think about moth example; the black ones were less frequently the "insects du jour")

Proximate explanations:

These don't try to explain function of characteristic. They explain the mechanism/how: What exact stimuli bring on the characteristic?

What physiological changes are involved in the characteristic? (back to those darned dirty moths)

Nonfunctional evolutionary changes

Know Lewontin and Gould's arguments re. spotted hyena (p. 71). Basic point is that not all genetic changes occurred because they helped the organism to adapt to new environmental circumstances.

Genetic drift

Genetic variation that occurs by chance and not by selection mechanisms.

Charles Darwin

igi n of Species

Moths prior to 1848

Moths after 1898

Ethology: The Study of Species-Typical Behavior Patterns

Focus Of Ethology

Behavioral differences among species that could reflect their evolutionary heritage.

Fixed Action Patterns (FAPs)

Motor program that is "hardwired".

Involves a repertoire of stereotyped movements.

Behaviors are characteristic of a species and their structural features.

Sign stimuli: those stimuli (e.g., red belly) that elicit the FAP (e.g., attack).

(Are red sports cars sign stimuli for road rage??)

Examples of FAPs and sign stimuli (of many available)

Tinbergen's stickleback research.

Red underbelly serves as sign for vigorous attacks by other male sticklebacks. (See Gray, p. 73).

Human yawning (releases yawns in others).

Human smiling (releases smiles in others).

Human eyebrow flash.

Baby schemas.

Lorenz' research on Baby schemas

Certain stimuli indicating "babyness" release an innate tendency by us to feel sympathetic distress and to care for the young.

Some of releasing stimuli discussed are:

• Proportionately larger head than body.

• Forehead that protrudes relative to rest of face.

• Extremities that are short and thick.

• Round body shape.

• Soft elastic body surface.

• Chubby (round) cheeks.

Some ethologists note a connection between baby faces and sexual attractiveness. Why would there be a connection, do you think?

• Ekman and Friesen's research on universal emotional expressions (study Gray).

Why Study Fixed Action Patterns?

They help us to figure out how behaviors/characteristics evolved, since FAPs are slightly different in species that are related to one another

I think the most important point here is that not all behavior should be seen as rigid or inflexible fixed action patterns in response to sign stimuli. The characteristics that we inherit biologically "prepare" us to be able to quickly learn some behaviors and less quickly learn (or never learn) others.

Just as we humans seem biologically prepared to learn a language or walk on two legs, other organisms are biologically prepared to do things we could never learn!

Bees' biological heritage prepare them to be sensitive to ultraviolet light and respond to honey guides; dogs are sensitive to more smells and sounds than we could ever imagine (let alone learn); bats and sharks to sonar, etc.

Tracing the Evolution of Species Specific Behaviors

We can think of evolution in terms of a HUGE tree with multiple branches. The trunk of the tree represents the common heritage we share. But, the tree branches off in different directions and branches off again and then branches off again (...). Any limb connecting two branches means organisms at some point have shared a common ancestor (e.g., lions and tabby cats have the same great- great- great-...grandparents). But, at some point on the tree the organisms have split off and gone in different genetic directions.

We can graph what the tree of evolution looks like (where it branches; where organisms split from one another) by studying similarities among species.

Gray distinguishes two types of similarities:

(1) Analogies

Similar characteristics reflecting convergent evolution

The two species share a characteristic, BUT NOT because a common ancestor passed along the characteristic to the species. The two evolved the characteristic because of some similarity in their habitats or lifestyles. THIS similarity made it adaptive for the characteristic to evolve in that environment.

The similarities in analogies are often in function and gross form of the characteristic. But, when you look closer at them (e.g., their neural and muscular nature), they are very different.

Examples

Dolphins, fish, and penguins have fins

Bats, birds, and mosquitoes have wings

Elephants, boars, and walruses have tusks

Snakes and bees produce venom

Ostriches, giraffes, and brontosauruses have long necks

Ducks and otters have webbed feet

(2) Homologies

Similar characteristics reflecting a common ancestor

The two species share a characteristic, BECAUSE a common ancestor passed it along to them. Obviously, then, more closely related species will show a greater number of homologies.

Examples

Vertebrae

Two eyes

Noses, mouths, teeth, ears, limbs, skin

Because homologies actually involve shared genes, they are very similar in terms of underlying physiology and construction, even though "on the surface," they may appear different and may function differently.

I've noticed that some students at USU object to the stated "relatedness" between humans and nonhuman primates or other animals. They object to attempts to understand human characteristics in terms of evolutionary, known genetically, related "nonhuman" behavioral proclivities. Frans de Waal, a famous behavioral ethologist, has the following comment on this score:

"We have a tendency to compare animal behavior with the most dizzying accomplishments of our race, and to be smugly satisfied when a thousand monkeys with a thousand typewriters do not come close to William Shakespeare. Is this a reason to classify ourselves as smart, and animals as stupid? Are we [humans] not much of the time considerably less rational than advertised?....A chimpanzee stroking and patting a victim of attack or sharing her food with a hungry companion shows attitudes that are hard to distinguish from those of a person picking up a crying child, or doing volunteer work in a soup kitchen. To classify the chimpanzee's behavior as based on instinct and the person's behavior as proof of moral decency is misleading, and probably incorrect. First of all, it is uneconomic in that it assumes different processes for similar behavior in two closely related species. Second, it ignores the growing body of evidence for mental complexity in the chimpanzee, including the possibility of empathy"

[pp. 209-210; de Waal, F. (1996). Good natured: The origins of right and wrong in humans and other animals. Cambridge: Harvard University Press.

LINK: Ethological Experiments

LINK: Konrad Lorenz

LINK: The Science of Attraction

LINK: Faceprints Experimental Program

Sociobiology: The Comparative Study of Animals' Social Systems

Why do organisms engage in aggressive behavior? What functions does it serve?

Territorial Aggression vs. Dominance-Related Aggression

Altruism

Why would animals even live in groups?

Obvious pro: greater protection from outside predators

Obvious con: can more readily catch diseases & be attacked by others in group

Altruism has evolved to counteract some of disadvantages. Also benefits one's own genes being passed on.

The Altruist Test

Are you completely altruistic (i.e., self-sacrificing)?

When you have only a few minutes to save people, who are you most likely to save from a burning building?

the cop next door?

your bishop?

your bank's president?

THE president?

your mother/father?

your two grandparents?

eight of your first cousins?

your brother?

your own boy or girl?

yourself?

Why did you make this choice?

How about other organisms?

How altruistic are they?

(cf. Robert Wright, 1994, The Moral Animal, Vintage Books):

Bees and wasps sacrifice themselves for others.

Ants defend colony by self-destruction.

And, why would childless ground squirrels sound a call of alarm after sighting a feared predator, thereby committing what Wright called evolutionary suicide.

Idea of Kin Selection and Altruism

Kin selection is a main concept in sociobiology. Basic idea is that we act to promote our kin's success because of shared genes. This enhances chance of the genes getting passed on.

Kin selection occurs in various ways (e.g., parental investment). Altruism is one way it is seen.

Hamilton (1963, 1964): To understand altruism, need to think of it not in terms of individual's survival but in terms of its genes' survival.

The squirrel by sounding the alarm ends up saving some of its relatives. Some of them will possess the same gene for "sounding an alarm." This passes on gene.

So, who would you save?

Consider your answer in light of British biologist Haldane's joking comment (cf. Wright, 1994) that he:

Would never give life for his brother but for "two brothers or eight cousins."

Why did he say this?

You share 50% of genes with your brother.

You share 12.5% of genes with first cousins.

Haldane's chances of passing on the gene are greater by saving 8 cousins than one brother.

Hamilton's equation clarifies the "truth value" of this joke:

Equation involves three factors:

Cost to altruist (c):

Costs could be losing own life; not passing on own genes

Benefit to recipient (b):

Benefits could be being saved; being able to reproduce

Relatedness of altruist and recipient (r):

how genetically close altruist and recipient are. Examples:

r = 50% for full siblings

r = 25% for half-siblings, nieces, nephews, aunts, uncles

r = 12.5% for first cousins, etc.

In Hamilton's view: Genes for altruism (sacrificial behaviors) will be rampant in the group only when c is less than b * r.

So, kin selection theory really says:

We will direct "altruism" to relatives most closely genetically related to us (talk about nepotism!). Evidence bears this out.

Ground squirrels sound the alarm more in presence of close relatives. Also seen in chimps, other nonhuman primates, and ourselves.

Huge self-sacrifices are made by bees, wasps, social ants than other insects. This order of insects also have a huge r (75%).

We, too, help each other, but to a far lesser extent.

To some, the term kin selection is a misnomer. It isn't the individual or the family that is being saved. It is the gene. What some have called the selfish gene (Dawkins, 1976). Sounding the alarm appears altruistic at level of organism, but it is actually pretty "selfish" at the level of the gene (since the gene "gets its way" of having a good chance of being passed on through the survivors).

Idea of Reciprocal Altruism: So why help an unrelated other?

Helping nonkin helps self survive & therefore reproduce if the nonkin reciprocates the help back.

Example

Vampire bats or Bat Friends: Unsuccessful bats will receive regurgitated blood from nonrelative bats. The new "bat friend" returns favor later on. Cheaters are recognized. If they fail to reciprocate later, they are less likely to be "helped" again in future.

Some sociological thoughts about humans: Fallacies to avoid

Naturalistic Fallacy

Assuming that what is natural is somehow "right" or more moral. Equating what "is" (nature) with what is moral or how things "ought" to be.

Spencer used this argument to justify all manner of dastardly deeds and conditions in society (see Gray).

G.E. Moore: Wrong! Inferring values from evolution or any aspect of nature is the naturalistic fallacy.

John Stuart Mill (1847): nature "impales men, breaks them as if on the wheel, casts them to be devoured by wild beasts, burns them to death, crushes them with strones like the first Christian martyr, starves them with hunger, freezes them with cold..." (cf. Wright, 1996, p. 331).

Deterministic Fallacy

Assuming that Biology (our genetic heritage) is Destiny and that we can't volitionally control lots of the things we do.

Wright enumerates some sad examples of this assumption in our own culture:

The Twinkie Defense

Junk-food diet leading to diminished capacity while commiting a murder.

PMS, high testosterone, PTSD, battered women's syndrome, depression-suicide syndrome, low levels of serotonin (etc.) are used to excuse the person for committing fairly annoying to highly immoral behaviors .

So what do we do? Good question.

(Cartoons by Mark Parisi. Used by special permission. For many more, visit his site.)