Psychology Chapter 3

How are different expressions of genes produced?
Genes can turn on and off
the contributions of heredity to our psychical structure and behaviors.
the contributions of environmental factors and experience to our physical structure and behaviors.
Francis Galton
was also Charles Darwin’s cousin, was the first to use the phrase “nature versus nurture” in his discussion of intelligence, believing that intelligence was largely the result of inheritance.
o the “nature versus nurture” concept describes the contrast between heredity and environment.
One copy of your genome was provided by your mother’s egg, and the other by your father’s sperm. Each parent contributes a set of 23 chromosomes, which in turn are composed of many molecules of DNA.
an individual’s profile of alleles. One’s genotype interacts with the environment to produce observable characteristics known as a phenotype.
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Observable characteristics.
• Ex. your genotype might include a gene for blonde hair and another for brown (genotype is the two alleles), but your phenotypical, or observable trait of hair color is light brown hair.
small segments of DNA located in a particular place on a chromosome. Each gene contains instructions for making a particular type of protein.
Gene expression
the process in which genetic instructions are converted into a feature of a living cell.
o each cell contains the instructions for an entire human organism, but only a subset of instructions is expressed at any given time and location.
one of several versions of a gene, as in having an A, B, or O blood type allele. Alleles can give rise to different phenotypical traits.
o Many alleles can occur for a given gene, but a single individual receives only two, one from each parent.
having two of the same alleles for a gene. (both parents contribute the same type of allele for that gene).
having two different alleles for a gene. (each parent contributes a different allele for the same gene).
a feature of an allele that will only produce a phenotype in the homozygous condition.
a feature of an allele that will determine a phenotype in either the homozygous or heterozygous condition.
• However, in many cases, one allele does not entirely dominate another. (ex – getting light brown hair instead of dark brown or blonde)
Genetic Variation
o When a parent’s cell divides to make an egg or sperm cell, each resulting cell contains 23 chromosomes, one chromosome from each of the parent’s original 23 chromosome pairs. As a result, a single human can produce eggs or sperm with 2^23 (8,388,608) different combinations of his or her chromosomes.
the probability that two people share copies of the same allele from a common ancestor.
Sex Chromosomes
(males are XY and females are XX)
o 22 of the 23 pairs of human chromosomes from each parent are perfectly matched (each gene has a corresponding gene on its partner). The remaining pair, the X and Y sex chromosomes, does not carry the same genes.
o Most of the genes located on the Y chromosome are involved with male fertility.
o The X chromosome contains genes not duplicated on the Y chromosome that influence a wide variety of characteristics.
o Generally, if a female receives a healthy gene on the X chromosome from one parent and a defective gene on the X chromosome from her other parent, she will be a carrier of the condition, but will not experience it herself. (the healthy X chromosome will offset the other unhealthy X chromosome)
o In contrast, a male receiving a defective gene on the X chromosome from his mother will have the condition. Because there is no equivalent gene on the Y chromosome to offset the defective recessive gene, it will be expressed.
• as a result, conditions such as hemophilia and red-green colorblindness are much more frequent among males and referred to as sex-linked characteristics.
the study of gene-environment interactions in the production of phenotypes.
o When factors other than the genotype itself produce changes in a phenotype, we say that an epigenetic change has occurred.
o Epigenetic change often works by influencing gene expression, the process by which the DNA forms proteins that contribute to features of living cells. The environment can determine if and when a particular gene is activated.
o Epigenetic change provides a clear example of how the human mind responds to the interplay between nature and nurture.
Behavioral Genetics
the scientific field that attempts to identify and understand links between genetics and behavior.
• These links can help explain individual differences between human beings as well as the differences we see between our species and others.
the statistical likelihood that variations observed in a population are due to genetics.
o Heritability is usually presented as a ratio of the amount of variation observed in a population due to genetics relative to the total amount of variation due to both genetic and environmental influences.
3 Common Misconceptions about Heritability
1) Heritability always refers to populations, not to individuals.
2) Heritability cannot be assessed without taking the environment into account. If the environment is held constant (everybody is treated exactly the same way), the heritability of a trait will appear to be high – because the heritability will be exaggerated. In variable environments, heritability will be lower.
3) Another common misunderstanding of behavioral genetics is the belief that we can identify a “gene for” a particular behavior (ex. the “gene for” alcoholism).
descent with modification from a common ancestor
• The human genome is the product of millions of years of evolution.
Charles Darwin
• In his book, The Origin of Species, Charles Darwin proposed that species evolve or change from one form to the next in an orderly manner.
o Darwin found this because he was well aware of the procedures used by farmers to develop animals and plants with desirable traits by mating particular individuals to each other.
• Darwin suggested that the pressures of survival and reproduction in the wild would make the choice determining which traits are passed along to the next generation, a process he named natural selection.
Natural Selection
the process by which survival and reproduction pressures act to change the frequency of alleles in subsequent generations.
• Organisms that survive long enough to reproduce would pass their traits along to the next generation. Organisms that did not reproduce would not have the opportunity to pass their traits along to future generations.

* Natural selection favors the organism with the highest degree of fitness.

Gregor Mendel
discovered ways to outline and predict the inheritance of particular traits, like the color of flowers, in his research on pea plants, accounting for the variations he observed in a particular trait.
Mechanisms of Evolution
Genetic Drift
errors that occur when DNA is replicated.
o Mutant alleles that provide some advantage often spread through the population, but most mutant alleles that result in a disadvantage disappear from future generations.
o The average human baby is born with 130 new mutations, but the vast majority have no effect.
occurs when organisms move from one geographical location to the next.
o phenotypical traits that are advantageous in one environment might be less so in another
Genetic Drift
change in a population’s genes from one generation to the next due to chance or accident.
the ability of one genotype to reproduce more successfully relative to other genotypes.
o This concept of fitness includes survival to adulthood, ability to find a mate, and reproduction.
o Fitness describes the interaction between characteristics and the environment in which they exist. – we need to consider nature within the context of nurture.
o Fitness varies across environments – characteristics such as long ears and long legs work in hot, desert climates, but short ears and legs conserve heat in colder climates.
a change due to natural selection. In other words, a species can respond to an environmental change by adapting. and features of the new phenotype may be referred to as adaptations.
o Adaptations can take many forms: they can be behaviors (such as jumping higher to avoid a predator) or anatomical features (such as eyes that can see color).
o Any adaptations that are “good enough” to contribute to the fitness of an organism will carry forward into future generations.
o A classic example of very rapid adaptation is the case of the English peppered moth
Evolution of the Human Brain
Our brain started off to be the size of chimpanzees brains, but over time it grew to be over half the time as the new branch of hominin’s — homo sapiens or humans emerged.
• This rapid brain evolution suggests that improved intelligence was quickly translated into substantial advantages in survival.
• The major factor distinguishing human intelligence from the intelligence of other species is the richness and complexity of the social behavior supported by the human brain.
• The challenges that humans face and our social behavior required the evolution of a special brain.

However, the brain has not changed much over the past centuries. Although it continues to evolve, it is not really growing.
• It is likely that environmental factors, including nutrition and education, might account for the improvement of our brains.

Evolutionary Psychology
: the psychological perspective that assumes our current behavior exists because it provided survival and reproductive advantages to our ancestors.
• The evolutionary psychology approach is a direct descendant of the functionalism supported by William James.
o Functionalism implies that behavior is seen as promoting survival, as opposed to being random and pointless.
• The goal of evolutionary psychology is to explain how the patterns of behavior we share with other human beings have been shaped by evolution.
Origins of Social Behavior
• A number of factors are believed to influence the social behavior of any particular species, including mating systems, the availability of resources such as food, water, and shelter, the exposure to predators, and competition.
• One of the outstanding features of human beings is our rich and essential social nature.
• To understand the evolution of social behavior, we need to explore its advantages for survival and reproduction.
4 Types of Social Behavior
Cooperation (both win)
Selfishness (one wins through cheating, the other loses)
Altruism (one chooses to lose for the benefit of the other)
Spite (both lose)
sacrifice of one’s self for the benefit of another individual.
o altruism is widespread in the animal kingdom.
o Darwin stated, “A tribe including many members who, from possessing a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good would be victorious over most other tribes; and this would be natural selection.”
Reciprocal Altruism
Help you provide another person when you expect the person to return the favor in the future.
o In cases of reciprocal altruism, it is customary to help another individual when you can reasonable expect the other individual to return the favor at some future date.
Sexual Selection
the development of traits that help an individual compete for mates.
• Sexual selection is influenced by the different investments in parenting made by males and females.
• The mother can maximize her children’s chance of survival by choosing a father who will not only pass along healthy genes but will participate in the raising of children.
o Women have the ability to make very accurate predications of a man’s interest in children, simply by looking at a photograph of his face. Men with facial features correlated with high testosterone are viewed as less likely to participate in childrearing than are men with facial features correlated with lower testosterone.
Two types of sexual selection
Intersexual Selection and Intrasexual Selection
Intrasexual Selection
(“intra” means within) – members of one sex compete with each other for access to the other sex
• ex. male deer engage in fights that determine which males are able to mate and which are not
Intersexual selection
(“inter” means between) – characteristics of one sex that attract the other might become sexually selected
• ex. the coloration on peacocks.
practices, values, and goals shared by groups of people.
• Human cultures arise from knowledge that is transmitted socially – through social interactions.
• Experiences shaped by culture, like other types of experiences, interact with survival and reproductive pressures.
Birds of a Feather Flock Together Approach
• In terms of social psychology, “birds of a feather really do flock together” in that perceived similarities are important to many relationships – we like to believe that our choice of mate is based on factors like physical attractiveness and mutual interests and values.
• The evolutionary approach, however, suggests that another type of compatibility is important for romantic relationships – a compatibility of genes that contribute to the immune system.
o Looking at a cluster of genes known as the major histocompatibility complex (MHC), shows our tendency toward sexual selection. This type of sexual selection operates on traits in one sex that influences the choices by others.
o Different configurations of the MHC genes produce distinctive body odors that are easily detected and distinguished from one another. Men and women prefer smells associated with MHC genotypes that were different than their own.
*We must stress the importance of the importance between the interaction between nurture and nature in shaping the mind and a human being
• Viewing nature and nurture as interacting influences on our behavior reassures us that we are not somehow helpless captives of our genes. They are certainly an important part of who we are, but our choices and experiences make major contributions to the final product as well.