Each of us has a unique package of looks, language, personality, interests, and cultural background.
We are the leaves of a tree.
Common behavioral tendencies are also shared by our human family.
Our brain architecture allows us to sense the world, develop language, and feel hunger.
We prefer sweet tastes to sour.
The spectrum is divided into similar colors.
We feel drawn to behaviors that protect offspring.
Our social behaviors show our kinship.
As adults, we prefer the company of those with attitudes and attributes similar to our own, even if they are named Gonzales, Nkomo, Ahmadi, Smith, or Wong.
We know how to read one another's smiles and frowns.
As members of one species, we affiliate, conform, return favors, punish offenses, organize hierarchies of status, and grieve over a child's death.
Humans can be found dancing and worshiping, playing sports and games, laughing and crying, living in families and forming groups, and visiting from outer space.
Universal behaviors define our human nature.
The scientific story of how our genes and environments knit us together is told in this chapter.
Every step of the way, research shows that nature and nurture shape our development.
The heredity that interacts with our experience to create both our universal nature and our individual and social diversity is behind the story of our body and brain.
Few would have thought that every cell nucleus in your body has a genetic master code.
It's as if every room in the world's tallest building has a book in it.
Your mother's egg and your father's sperm contributed to the 46 chapters of your book of life.
The words of each chapter are called a olecules.
The environmental events that turn on genes are like hot water allowing a tea bag to express its flavor.
Every human cell has a nucleus made up of two strands of DNA connected in a double helix.
The development of a person's individual development is influenced by the expression of genes.
Every other human is almost identical to you.
Human genome researchers have found a common sequence.
The shared genetic profile is what makes us humans.
We are not different from our Chimpanzees.
Humans and Chimpanzees are 96 percent alike at a genetic level.
That 0.6 percent difference matters.
It took a human, Shakespeare, to weave 17,700 words into a masterpiece.
Their genomes differ by less than 1 percent.
They display different behaviors.
Chimpanzees are dominated by males.
Female led Bonobos are peaceable.
Geneticists and psychologists are fascinated by the occasional variations in human genes.
Variations from the common pattern give clues to why one person is different from another.
Your and mine have the same genes.
Most of our genes are complex.
Different genes interacting with your environment may affect the size of your face, spine, leg bones, and so forth.
Intelligence, happiness, and aggressiveness are all influenced by many genes.
One of the big findings of behavior genetics is that there is no single smart gene, gay or straight.
Our differences are influenced by many genes of small effect.
Our genes explain both our human nature and our human diversity.
Knowing our heredity only tells part of our story.
Our genetic predispositions interact with environmental influences to form us.
The following cell structures should be placed in order from smallest to largest.
Behavior geneticists wish for two types of experiments to tease apart the influences of heredity and environment.
The first would change the home environment.
The home environment would be controlled by the second.
Nature has done this work for us, even though it would be unethical.
It helps explain why one twin may have a higher risk for certain illnesses and disorders.
One of every three sets of identical twins has a different placenta.
One twin's placenta may provide slightly better sustenance, which may contribute to a few identical twin differences.
Fetal partners share the same environment as brothers and sisters, but they are not the same.
They share the same environment as brothers and sisters, but they are genetically different.
It is possible for shared genes to translate into shared experiences.
The co-twin of the affected twin has a 1 in 3 risk.
More than 15 million identical and fraternal twin pairs have been studied to understand the effects of genes and environments.
Many behaviors are influenced by genes.
Drinking and driving convictions are 12 times more likely for people with an identical twin with such a conviction.
The behaviors of identical twins remain the same as they grow older.
Affirmative twins look different than identical twins.
Nancy Segal used a clever approach to compare personality similarity between identical twins and unrelated pairs.
The identical twins had the same personality.
Other studies have shown that identical twins who were treated differently by their parents were not more alike than identical twins who were treated the same.
Individual differences are explained by genes.
Genetically unrelated look-alikes tend not to have the same personality.
Imagine a science fiction experiment where a mad scientist decides to separate identical twins at birth and raise them in different environments.
Jim Lewis woke up next to his second wife after divorcing.
Jim left love notes around the house to make this marriage work.
He thought about his loved ones as he lay in bed.
Jim spent part of the day in his basement woodworking shop building furniture, picture frames, and other items, including a white bench in his front yard.
Jim liked to drive his car, watch stock-car racing, and drink beer.
Twins are going to deliver Christmas presents to each other near Flitcham, England.
Jim had occasional headaches and a high blood pressure that may have been related to his smoking habit.
He had lost some of the weight he had gained.
He was done having children after having a vasectomy.
Jim Lewis was extraordinary because at the same time, there was another man named Jim who was also true, right down to the dog's name.
Thirty-seven days after their birth, these genetically identical twins were separated, adopted by blue-collar families, and raised with no contact or knowledge of each other's whereabouts until the day Jim Lewis received a call from his genetic clone.
The film shows the two girls growing up in different parts of the country.
Twins dislike tomatoes, olives, and messy rooms and share a passion for chocolate.
One month later, the brothers became the first of many separated twin pairs to be tested.
Jim Lewis was wrong.
Despite 38 years of separation, the Jim twins were virtually the same person tested twice.
Both women were married to each other.
The last item is a joke.
Judith Rich Harris noted that it is not weirder than other reported similarities.
The media publicity aided in locating and studying 74 pairs of identical twins.
They continued to find similarities between tastes and physical attributes, as well as personality, abilities, attitudes, interests, and even fears.
More than 200 separated twin pairs were identified in Sweden.
Compared with samples of identical twins raised together, the separated identical twins had less similarities.
If the twins were genetically identical, they were more alike.
They did not amplify their personality differences when they were separated shortly after birth.
They note that if two strangers were to compare their life histories, they would find many similarities.
Twin researchers said that separated twins do not have the same characteristics.
Twin research was done in Minneapolis, the home of the Minnesota Twins baseball team.
The data from personality assessments is clouded by the reunion of many separated twins.
Twins are usually placed in the same homes by adoption agencies.
The striking twin-study results helped shift scientific thinking towards a greater appreciation of genetic influences.
For personality or any other trait, we can ask whether adopted children are more like their biological parents, who contributed their genes, or their adoptive parents, who contribute a home environment.
The stunning finding from studies of hundreds of adoptive families is that, apart from identical twins, people who grow up together, whether biologically related or not, do not much resemble one another in personality.
Two children raised in the same home are not likely to have the same personality quirks as each other.
Other primate's personality is shaped by heredity.
The social behaviors of macaque monkeys are similar to those of their biological mothers.
Questions like that fuel behavior geneticists' curiosity.
The genetic leash may limit the family environment's influence on personality, but it doesn't mean that adoptive parenting is pointless.
It is heartening to know that parents influence their children's attitudes, values, manners, politics, and faith.
Jack Yufe, raised a Jew and a member of Germany's Hitler Youth, illustrated this.
"If we had been switched, I would have been the Jew, and you would have been the Nazi", said Oskar to Jack.
Child neglect and abuse are rare in adoptive homes.
It is not surprising that most adopted children thrive, especially when they are infants.
Seven in eight of the children adopted have a strong attachment to one or both adoptive parents.
As children of self-giving parents, they have grown up to be more self-giving and altruistic than average.
Many scored higher than their biological parents on intelligence tests, and most grew up to be happy and stable adults.
Children who were adopted as infants grew up with less problems than children who were raised themselves, according to a Swedish study.
Adoption benefits most children regardless of personality differences between adoptive family members.
Hitler's right-hand man and founder of the Nazi Gestapo was the brother of a different person.
Albert Goering was a quiet man and worked to save Jews who were being killed by his brother's regime.
Adoption is one of the biggest gifts of love, and Faith Hill and Steve Jobs both benefited from it.
Twin and adoption studies are used to understand how much variation is due to genetic makeup and how much is due to environmental factors.
Some studies compare twins with the same genes, while others compare twins with different genes.
They compare adopted children with their biological parents.
Twins raised together or separately are compared in some studies.
Babies differ before their first breath, as most parents will tell you.
One aspect of personality that is quickly apparent is emotional reactivity and excitability.
Twins with similar temperaments are often identical.
Differences in temperament can persist.
The most reactive 9-month-olds are the most emotionally reactive newborns.
Young adults who are emotionally intense tend to be more intense.
In one study of more than 900 New Zealanders, 3-year-olds who were emotionally reactive and impulsive became more aggressive and conflict-prone.
The genetic effect can be seen in differences in metabolism.
Anxious infants have high and variable heart rates.
They become more aroused when facing strange situations.
Our personality is formed by our biology.
Asking whether our personality is a product of our genes or our environment is like asking whether a field is larger because of its length or width.
We can ask if personality differences are influenced by nature or nurture.
Behavior geneticists can estimate the heritability of a trait using twin and adoption studies.
For general intelligence, heritability has been estimated to be 66 percent.
Depending on the range of populations and environments studied, the heritability of a trait may vary.
Intelligence varies from study to study.
Mark Twain had a fictional idea of raising boys in barrels to age 12 and feeding them through a hole.
Their test score differences could only be explained by their genes.
Heritability would be close to 100 percent with the same environment.
As environments become more similar, heredity becomes the primary source of differences.
If all people had similar heredities but were raised in vastly different environments, heritability would be much lower.
Nutrition and the environment are more important than genes in explaining why today's adults have grown.
The average American male stood 5 feet 7 inches in 1850 and 3 inches in the 1980s.
Human genes have not changed in this eyeblink of time.
Genes and environment matter.
Group differences are not heritable individual differences.
A new social context can change aggressiveness.
Today's peaceful Nordics have many of the same genes as their Viking warrior ancestors.
Our enormous adaptive capacity is the most important hallmark of our species.
The same human trait can be found in virtually every environment.
Other qualities are only expressed in certain environments.
If you go barefoot for a summer, your feet will develop a biological adaptation to friction.
Your neighbor will be a tenderfoot.
The environment has an effect on the two of you.
It is the result of a biological mechanism.
Our shared biology gives us developed diversity.
Gene-environment interaction studies can reveal who is most at risk of permanent harm from stress or abuse and who is most likely to benefit from interventions.
In 2015, Scott and Mark embarked on a study that was out of this world.
Scott was in the International Space Station for over 300 days.
His twin, Mark, was on Earth.
Twins underwent the same tests.
The study results will help scientists understand how genes and environment interact.
Humans are influenced by teams of genes.
The genes influence how quickly the stomach tells the brain.
How much fuel the muscles need, how many calories are burned off, and how efficiently the body converts extra calories into fat might be decided by others.
Genes are not solo players.
Some of the genes that are involved in body weight, sexual orientation, and impulsivity can be found in the genetics of behavior.
The genes can either be active or inactive.
Rather than acting as blueprints that lead to the same result, genes react.
An African butterfly that is green in the summer turns brown in the fall.
The genes that produced green in one situation will produce brown in another.
If a mark instructs the cell to ignore any genes present in that segment, those genes will be turned off, which will prevent the DNA from producing the proteins normally coding by that genes.
One geneticist said that things written in pen can't be changed.
That's what it is.
You can write things in pencil.
That is epigenetics.
Environmental factors such as diet, drugs, and stress can affect the epigenetic molecule that regulates gene expression.
Rats lick their infants.
Infant rats were deprived of licking in the experiments and had more epigenetic molecules blocking access to their brain's "on" switch.
The animals with above-average levels of free-floating stress hormones were more stressed.
The effects of childhood trauma, poverty, and malnutrition may last a lifetime because of Epigenetics.
At the deepest level, life events can mark us.
Child abuse can leave its fingerprints in a person's genome.
Some epigenetic changes are passed down to future generations.
In one experiment, mice whose grandparents learned to associate the smell of orange blossoms with shock were startled when first exposed to the scent.
Stresses or pollutants that your parent or grandparent experienced could affect your health and well-being.
Holocaust trauma survivors shared their epigenetic alterations with their children.
Why only one member of an identical twin pair may develop a genetically influenced mental disorder may be solved by Epigenetics research.
Epigenetics can help explain why identical twins look different.
Scientists studying mice have found that exposure to certain chemicals can cause genetically identical twins to have different-colored fur.
Canadian Senator Murray Sinclair, seen here with Prime Minister Justin Trudeau, was honored for an in-depth report on the devastating effects of Canada's long running residential school program that removed aboriginal Canadian children from their families.
You can check your answer by clicking on the e-book and Appendix C of the printed text.
According to research, trying to answer these questions on your own will improve retention.
The structures made from DNA are called threadlike.