NATURE, NURTURE & HUMAN DIVERSITY

Nature vs. Nurture If Jaden Agassi, son of tennis stars Andre Agassi

and Stephanie Graf, grows up to be a tennis star, should we attribute his superior talent to his Grand Slam genes or to his growing up in a tennis-rich environment?

This issue is of interest to behavior geneticists who study the relative power and limits of genetic and environmental influences on behavior.Environment: every non-genetic influence, from

prenatal to the people and things around us.

Heredity DNA (deoxyribonucleic acid): contain the genetic

code in the sequence of its nitrogenous bases for the synthesis of proteins.

Genes: composed of DNA and carry the genetic code for a specific trait or characteristic

Chromosomes: threadlike structures made up of genes and proteins

Genome: the complete genetic instructions of an organism, consists of all the genes and their genetic material found on the organism’s chromosomes.

Heredity (cont’d)

Human Genetics Humans have 46 chromosomes (23 pair) in each

of their somatic (body) cells. 22 pairs (autosomes) control all genetic traits

except for those traits found on the single pair of sex chromosomes

• Male: XY – Female XX Gametes: sperm and egg; each contain 23

chromosomes (1/2 the number of the body cells).

Fertilization: when a sperm nucleus joins with an egg nucleus , a zygote is formed, restoring the human chromosome number to 46.

Gender Development in Utero The Y chromosome contains a single gene that

triggers the testes to develop and produce testosterone which leads to the development of male genitalia in about the 7th week of development.

If low levels of testosterone are released in the uterus, a female fetus will develop

During the 4-5 months of prenatal development, sex hormones bathe the prenatal brain

Different patterns of development for males & females occur under the influence of these sex hormones• Males: testosterone Females: ovarian hormones

Traits Trait: a genetically determined characteristic;

controlled by a pair of genes (one from mom and one from dad)

Gene Complexes: a group of genes that are responsible for the expression of a given trait.

Heritability: the proportion of variation among individuals in a trait that is attributable to genetic factors. For example, current estimates place the

heritability of intelligence at about 50 to 70 percent. The heritability of a trait may vary, depending on

the range of populations, and environments studied.

Identical vs. Fraternal Twins

Twin Studies MZ twins = monozygotic (identical ) twins DZ twins = dizygotic (fraternal) twins By studying MZ twins and DZ twins the relative

importance of genetics and environment expression of traits and behavior

Research findings indicate that identical twins are much more similar than fraternal twins in abilities, personality traits, and even interests.

Separated Twins Research Researchers studied twins separated at birth and

re-united later in life. Similarities were found in intellect, personality,

attitudes, abilities, interests, fears, brain waves, and heart rate.

Critics point out that any two strangers of the same sex and age would probably have many coincidental things in common if they were to spend hours comparing their behaviors and life histories.

Furthermore, stories by or about individuals do not constitute scientific data, even if there are many of them.

Adoption Studies Adoption enables comparisons with both

genetic and environmental relatives.

Adoption Studies (cont’d)

Adoptees' traits bear more similarities to their biological parents than to their care-giving adoptive parents.

However, research does indicate that adoptive parents do influence attitudes, values, faith, manners, and politics.

Clearly nature and nurture shape one's developing personality

Temperament & Heredity Temperament: refers to a person’s stable

emotional reactivity and intensity. The infant's temperament includes inborn

emotional excitability. From the first weeks of life, some babies are more relaxed and cheerful, others are more tense and irritable.

These differences in temperament tend to endure. For example, the most emotionally intense

preschoolers tend to be relatively intense as young adults.

Molecular Genetics Subfield of biology that studies the molecular

structure of function of genes. • Today, genetic testing can reveal at-risk

populations for many diseases (including certain learning disabilities, depression, schizophrenia, & alcohol use disorder.)

• Prenatal testing now can include genetic testing which leads to ethical questions: In countries where males are more highly valued,

leads to high numbers of female fetal abortions Labeling a fetus “at risk” for a certain disorder

can lead to discrimination

Genetic Interactions Genes are not blueprints; they are molecules that

have the ability to direct the assembly of proteins that build the body.

The genetic protein assembly can be turned on and off by the environment, gene expression, or by other genes.

Any trait we see is the result of the complex interactions of many genes and countless other molecules.

Gene-Environment Interactions

What is Epigenetics?

Epigenetics is a mechanism independent of DNA sequence of bases that that determines which genes are turned on/off in a particular cell type, in different disease states, or in response to a physiological stimulus

Psychology & Evolution Evolutionary Psychologists: study the

evolution of traits and behavior using the principles of natural selection/

Natural Selection (Darwin)OverpopulationCompetition for limited resourcesSurvival of the fittest (those best adapted to

the environment)Reproduction (passing of fittest genes to

future generations)

Psychology & Evolution (cont’d) In a changing environment, sexual reproduction

and mutations are the two sources of variations that can lead to genetic changes and alterations in inherited traits

A number of human traits have been identified as a result of natural selection.Why do infants fear strangers when they become

mobile?Why are most parents so passionately devoted to

their children?Why do people fear spiders and snakes and not

electricity and guns?

Evolution & Human Sexuality Males and females, to a large extent, behave and think

similarly.

Differences are most evident in respect to reproductive behaviors.

Generally, men think more than women about sex, and men are more likely to think that casual sex is acceptable.

Why might natural selection have resulted in greater male promiscuity?

Men who had the trait of promiscuity were more likely to have their genes continue, and even spread, in the next

generation. And there is little cost to spreading extra genes.

For women, a trait of promiscuity would not greatly

increase the number of babies; it would also have greater

survival costs (pregnancy, once a life-threatening condition).

Human Mating Preferences Males pass their genes to future generations by

mating with multiple youthful and fertile appearing females.

Females look for maturity, dominance, affluence, and boldness in male mates.

Females look for one caring male to mate with since there are higher costs involved with pregnancy, nursing, and child rearing.

Evolutionary Perspective

Evolutionary psychologists explanations: Evolutionary psychologists explain these differences

by noting that compared with eggs, sperm are cheap.

While a woman cares for a single infant, a man can spread his genes by impregnating other females.

Women most often send their genes into the future by pairing wisely, men by pairing widely.

Criticisms: Critics argue that evolutionary psychologists make too

many hindsight explanations.

In addition, much of who we are is not hardwired.

Prenatal Environment Identical twins who share the same placenta are

more alike than those who do not, suggesting prenatal influences on psychological development.

One placenta may have a more advantageous placement that provides better nourishment and thus a better placental barrier against viruses.

Even when twins share the same placenta, one may get a richer blood supply and weigh more at birth.

Environment & Brain Development

Research indicates that young rats living in enriched environments develop thicker and heavier brain cortexes than those in impoverished environments.

Stimulated infant rats and premature babies gain weight more rapidly and develop faster neurologically.

Experience preserves activated neural connections while allowing unused connections to degenerate.

Parental Influences Research indicates that home influences account

for less than 10 percent of siblings’ personality differences.

The fact that two children from the same family are as different from one another as pairs of children selected randomly

from the population suggests that parents should feel less pride in their children's successes as well as less guilt over their failures.

Peer Influences Experiences with peers powerfully socialize

children. Immigrant children placed in peer groups of non-

immigrants quickly lose their parents' culture. Teens who start smoking typically have friends who

model smoking. Peers are important in learning cooperation, for

finding the road to popularity, and for inventing styles of interaction among people of the same age.

Parents vs. Peer Influences Parents have more

influence over the development of:

Education & career path

Cooperation Self-discipline Responsibility Charitableness Religion Style of interaction with authority figures

Peers have more influence over the development in the areas of:

Learning cooperation skills

Learning the path to popularity Choice of music & other recreational activities Choice of clothing &

other cultural choices Good and bad habits

Influences of Culture Culture: the enduring behaviors, ideas, attitudes,

and traditions shared by a large group of people and transmitted from one generation to the next.

All cultural groups evolve their own norms, rules that govern their members' behaviors.

Cultures vary in their requirements for personal space, their expressiveness, and their pace of life.

Cultural values impact child-rearing practices. For example, Westernized cultures raise their

children to be independent. Many Asians and Africans who live in communal

cultures focus on cultivating emotional closeness.

Influences of Culture (cont’d)

Cultures change over time. The rate of this change may be extremely fast.

In many Western countries, culture has rapidly changed over the past 40 years or so.

This change cannot be attributed to changes in the human gene pool because genes evolve very slowly.

Culture & the Self Individualistic Culture: nurtures an individual’s

personal identity Collectivist Culture: the individual identity is

the same as the group identity Individualist cultures (European) raise their children as independent individuals. Collectivist cultures (Asian) raise their children as interdependent.

Cultural Influences Culture & Child Rearing

Westernized Cultures Asian‐African Cultures Responsible for self Responsible to group Follow your conscious Priority to obedience Discover your gifts Be true to family-self Be true to yourself Be loyal to the group Be independent Be interdependent

Despite diverse cultural backgrounds, humans are more similar than different in many ways. We share the same genetic profile, life cycle, capacity for language, and biological needs.

Gender Similarities/Differences Based on genetic makeup, males and females are

similar, since the majority of our inherited genes (22 pairs of autosomes – somatic chromosomes) are similar.

Biological: Females enter puberty on average 2 years earlier

than males, have more fat than muscle, and generally have a longer life expectancy.

Gender DifferencesMental/Behavioral : Females are more prone to depression, eating disorders, and

anxiety. Males more often exhibit autism, ADHD, & antisocial personality

disorder. Aggression: Men express themselves and behave in more physically aggressive ways than do women. This aggression gender gap appears in many cultures & at various ages. In males, the nature of this aggression is physical.Social Power: In most societies, men are socially dominant and are perceived

as such. In 2005, men accounted for 84% of the governing parliaments.

Gender & Social Connectedness Males and females differ in their feelings of

belonging (connectedness), a disparity that is noticeable from a young age and continues as an individual gets older.

When playing, boys tend to engage in competitive group activity without much close, confidential, or affectionate dialogue.

Girls typically are more intimate with each other and play in smaller groups, frequently with one friend (more interdependent)

Girls are also less competitive and more supportive and empathic.

Gender & Communication Women take pleasure in talking face to face, use

conversation to explore relationships, text more often & talk longer on the telephone.

Men enjoy doing activities side by side, tend to use conversations to communicate solutions, and talk about things & actions

Gender & Biology In adulthood, parts of the frontal lobes, (verbal

fluency), are thicker in females. Part of the parietal lobes (space perception) are

thicker in men. Gender differences also appear in the hippocampus,

amygdala & in the volume of grey matter (neural bodies) & white matter (axons & dendrites)

Gender & Biology (cont’d) When prenatal testosterone levels are high in

females, we often see an increase in “tomboy” behavior. This may be due to people’s response to

more masculine features & boyish preferences & behaviors.

However, there is not a general pattern of gender identity change.

Gender & Biology (cont’d)

Until recently, in cases where a boy is born with an undersized or absent penis or loses his penis in a botched circumcision, physicians suggested surgery to create a female identity.

For many of these children sex-reassignment did not change their developing identities as males.

Transgender: individuals who gender identity or expression differs from that associated with the birth sex ( XX or XY).

Transsexual people act on their inner identities by living as members of the opposite sex, often undergoing hormone & sexual interventions to support their gender reassignments.

Gender Roles Gender roles: our expectations of the way men and women

should behave. Gender roles vary across cultures and time. In nomadic societies of food-gathering people, there is

little division of labor by sex, so boys and girls receive much the same upbringing.

In agricultural societies, women stay close to home while men often roam more freely. Such societies typically socialize children into more distinct gender roles.

Even among industrialized countries, gender roles vary. In North America, medicine and dentistry are

predominantly male occupations In Russia, most medical doctors are women, as are most

dentists in Denmark.

Gender Identity Theories Gender Identity: our sense of being male or

female. To varying degrees, we also become gender-

typed, acquiring a traditional male or female role. Social learning theory assumes that children

learn gender-linked behaviors by observing and imitating others and by being rewarded and punished, all which shaore our behavior

Gender schema theory assumes that children learn from their cultures a cognitive concept of what it means to be male or female and adjust their behavior accordingly.

Influencing Personal Development