Nature,Nurture, and Human Diversity
Twin study is a very effective way to figure out if twins are more influence by nature (DNA, genes, etc.) or by nurture (environment, the way we were brought up, etc). In order to see if nature or nurture has a bigger role in our behaviors, we need to control the home environment while varying heredity, and for this purpose identical twins and fraternal twins were studied. Identical twins, who develop from a single fertilized egg that splits in two, are genetically identical. Fraternal twins, on the other hand, are those who develop from separate fertilized eggs and not genetically identical. For identical twins, if one has Alzheimer's disease, the identical twin has a 60% of sharing the disease, whereas fraternal twin only has 30% of sharing. This difference suggests a genetic influence, but there are influences of siblings' unique experiences and shared environment also. So studies of identical twins who were reared in different environments were put in used to show a clearer picture of genetic and environmental influences. Jim Lewis and his twin brother, Jim Springer, are an example of this study. They were separate when they were born. Both of them lived their life in different environments with no knowledge of each other, but their behaviors are very similar to each other, from their habits to their dogs' names. One day Jim Springer was informed that he has an identical twin brother, so he called his brother and met him. Then they were given a test to measure their personality, intelligence, heart rate, and brain waves. The results were so alike that it almost feel like one person who took the test twice. This shows that genetic has a very large influence on the identical twins even though they were reared apart.
Another way to study the influence of nature versus nurture is the adoption study. This study requires two groups of relatives: the adoptees' genetic relatives (biological parents and siblings) and their environmental relatives (adoptive parents and siblings). With this we can see whether the adoptive children are more like their adoptive parents, who contribute a home environment, or their biological parents, who contributed their genes. The finding shows that the adoptive children who grow up in the same home environment do not much resemble one another in personality. Their personalities are influenced by genetic more than environment, but their attitudes, values, manners, faith, and politics are influenced more by their adoptive parents (environment). Adoptive children will most likely to have similar religious belief when they were reared together during adolescence. So again it's true that genetic factors influence the personalities of people, but environmental factors do influence their attitudes, manners, faith, and politics more than genetic factors.
We've talked about how nature and nurture can influence our behaviors. As we know, nature refers to influences from our genes and DNA, and nurture refers to the influences from the environment that we were raised and lived in. So what is genes and DNA? DNA (deoxyribonucleic acid) is the material that presents in nearly all living organisms. It carries the genetic information in the body's cell. Genes are distinct portion of DNA; they're the coded instructions for making everything the body needs, especially protein, and chromosomes are bundles of genes and DNA. Now that we know what genes, DNA and chromosomes are, let's look at molecular genetics. Molecular genetics is the new behavior-genetics research that tries to identify specific genes influencing behavior. Most human traits are influenced by genes, which means that some disorders; such as schizophrenia, aggressiveness, depression; are also influenced by genes. Molecular geneticists can take DNA from families that have had the disorder across several generations, both affected and unaffected family members, and look for the differences in their DNA. With this we may be able to tell would-be parents how their fetus' genes differ from the normal pattern and what that means, This is the benefit of molecular genetics since we can identify the genes that are associated with specific disorders to prevent the disorders, but there's a risk. Would labeling a fetus "at risk for a learning disorder" lead to discrimination? In China, testing for offspring's sex has enabled selective abortions of millions of "women" because boys are more highly valued in China than girls. This could cause some serious problems with the population and break the balance between boys and girls.
Parent Influences on Development
Parents are usually praised for their children's successes, but they're also blamed for their children's vices. So do the ways our parents raised us affect our behaviors? And how big is this influence? With this, we'll come back to identical twins again. Identical twin men, now age 30, were separated at birth and raised in different places by their respective adoptive parents. Both kept their lives neat, very very neat. When the first was asked why he felt the need to be so clean, his answer was because his mother was always being clean. She kept the house perfectly ordered and insisted that every little things need to be at its proper place. So he learned from her. When the man's identical twin, whom also a perfectionist, was asked the same question, he said that he's only reacting to his mother, who is an absolute slob. So we may had inappropriately credited or blamed our parents with things that they didn't contributed in. Yet parents do matter. Parenting may not affect us in personality measures, but it does contributes in our political attitudes, religious beliefs, and manners. When we eat, it may not matter whether we get our protein from eating chicken or beans, but we must have food. Likewise, it may not matter whether we grew up with parents who toilet trained us early or late, but parents do help us to have someone we belong to, someone who cares about us.
Let's talk about genders. Genders matter, but depending on which gender we are, our role might be different than someone's role. Role refers to a cluster of prescribed actions-the behaviors we expect of those who occupy a particular social position. So gender roles are our expectations of the way men and women behave. Thirty years ago, it was standard for men to initiate dates, drive the car, etc. and women to decorate home, buy children's clothes, etc. In the United States, employed men spend roughly one hour more per day working than women, and an hour a day less on household activities. So do gender roles reflect what is biologically natural for men and women? or is it the result of culture constructions? In nomadic societies (food-gathering people) boys and girls receive pretty much the same upbringing. However, in agricultural societies, women stay at home, work in the field, and stay home with children while men go herding cattle or sheep. These examples show that the diversity of gender roles vary across cultures and countries, and that culture has a big influence on it. Gender roles also vary over time. Long time ago women weren't granted the right to vote, but now they do. In 1960, one in 30 entering U.S. law students were women, but by the early twenty-first century, half were.