Introduction (Prologue):

Nature refers to the inherent characteristics of humans. For example; How genes, chromosomes, DNA etc. affect people can be known by analyzing human nature.

Nurture on the other hand is where people are brought up or in what environment they grow up; Because the effect of that environment also affects human behavior. Note that human behavior is influenced by both nature and nurture . So what we need to know is that how this nature and nurture influence our behavior (Nature and Nurture how influence our behavior) .

Nature : Genetic Influences on Behavior :

Do genes affect our behavior and mental processes?
Of course! Children inherit the physical characteristics of their parents. For example; Bright or dark skin, blue or brown eyes, tall or short height, these characteristics are naturally inherited from parents by their children!

Heredity is a very important subject in psychology! Because many aspects of our behavior are influenced by genes . Certain types of human behavior are not inherited; Rather, heredity seems to influence us in many ways; Such as general intelligence.

Genetic Studies of Nonhuman Animal Behavior :

Gregor Johann Mendel is called the father of genetics. how parental traits are expressed in plant offspring; In that regard, he discovered a very valuable property by experimenting with pea plants.

When he was testing physical qualities in the pea plant; He was then able to identify a specific trait and instill that trait in their offspring. Selective breeding can be applied to other animals too! Aggression or foraging ability in mice and emotions in monkeys are influenced by genes.

In 1976, scientists Ebert and Janet confined rats in a room in the forest to carry out the research on mice; Conducted research on selective breeding.

To obtain the 1st progeny, female rats were divided into 2 groups based on rat aggression. After that; Unselected male rats were randomly bred with these two groups. After pupation, 10 highly aggressive female mice and 10 calm female mice from each group were again separated and randomly bred.

It was then observed that the 10 more aggressive rat pups became more aggressive and the 10 calmer rat pups became calmer. So; The research shows that genes have a special influence on the behavior of the offspring.

It may seem that environmental influences in the study influenced the results of the study. Therefore; As an alternative research, Dutch psychologists also conducted research in a different environment and found similar results! This study reinforces that research. So; These data suggest that genes have a specific influence on behavior.

Genetic Studies of Human Behavior :

A selective breeding experiment in humans (as in mice) should never be carried out for ethical reasons. So; Research on the nature and nurture of behavior in humans becomes much more difficult. However; As an alternative to this research, the researchers found a way. That is research on twins and foster children.

Studies of Twins :

There are two types of twins and they are formed in two different ways. One of them is called a monozygotic (mono=1) twin; And the other is called dizygotic (di=2) twins.

Monozygotic Twins : When two children are born from a single fertile egg of the mother, then they are called monozygotic twins. In monozygotic twins it breaks during cell division of the cluster early in pregnancy; And if all goes well, two twins are born from these two clusters. Because these two twins come from the same egg; Just as they look similar, their genetic makeup is also similar.

Dizygotic Twins: In dizygotic twins, two separate fertilized eggs of the mother and two separate sperm of the father unite! These two fertilized eggs produce two twins called dizygotic twins. Even though dizygotic twins are born from the same womb at the same time, they are not genetically identical ! This is because they are born from separate sperm and egg like other children.

Monozygotic and dizygotic twins provide real data for psychologists’ research. Because; These two types of twins in the same domestic environment; to the same parents; And even when raised in the same neighborhood, their degree of genetic similarity varies.

A lot of research has been done based on genetic or genetic traits in human nature. One of the notable researches is; Taking IQ or Intelligence (IQ) tests of twins. The results of conducting this IQ test showed that monozygotic twins have nearly identical IQ scores .

On the other hand, dizygotic twins always have different scores from each other! Similarly, other studies have shown that body composition; muscle strength; Human psychological qualities and behavior, including the ability to act, are largely influenced by genes.

Studies of Adopted Children :

Research on foster children has also shown that genes influence human behavior! In this case, the IQ or intelligence measurement test is again conducted! The study found that the IQ scores of foster children were almost always equal to the IQ scores of their real parents .

Although they grow up with adoptive/foster parents; Yet their IQ scores resembled those of their real parents rather than those of their foster parents. The research shows that; Genes influence everything, including behavior and intelligence.

Molecular Genetic Mechanisms of Inheritance :

In the past it was believed that a person’s hereditary qualities are carried through his blood. But; At present we know that human hereditary qualities are carried through some genetic material called genes! Genes are called carriers of heredity.

Genes are found in all nuclei of human cells! Gregorian Johann Mendel hypothesized the existence of genes more than 100 years ago. After that; By the middle of the 20th century, genes were discovered with the advent of powerful electron microscopes.

Genes , Chromosomes and DNA:

Every cell in the body has tiny structures called chromosomes. This chromosome is called the unit that controls all visible and invisible traits . The gene is located on this chromosome.

Chromosomes are long strings of deoxyribonucleic acid, abbreviated as DNA . DNA is normally a twisted/twisted ladder that twists in both directions; It is called a double helix . The twisted turns of the double helix contain chemical elements called nucleotides.

DNA has four types of nucleotides; They are adenine (A), thiamine (T), guanine (G), and cytosine (C) . As the combination of various letters forms our intelligible information; Thus the body’s characteristics are formed by the genetic code of adenine (A), thiamine (T), guanine (G), and cytosine (C). Chromosome, the part of DNA that contains the information needed to affect different aspects of the body is called a gene. Chromosomes are located in DNA and genes are located in DNA .

Human chromosomes are arranged in 23 pairs. When cell division occurs during growth or repair of tissues/cells, an exact new copy/copies of chromosomes are produced in the new cell. But only when reproductive cells are formed, the chromosomes break from 23 pairs to 23.

Then, when the sperm and egg successfully combine in the fertilization process and become a new cell, it is called a zygote. In the zygote , the father’s 23 single chromosomes and the mother’s 23 single chromosomes again become 23 pairs .

If all goes well, the zygote implants itself in the mother’s uterus and the embryo begins to grow. This is how the genetic characteristics of both parents are transferred to the child.

Polymorphic Genes :

Small changes called mutations have occurred in the DNA of germ cells at various times throughout the history of human evolution. Most mutations damage organisms in such a way that they can no longer survive. But; Mutations also occur in genes; which helps organisms to survive and reproduce; So that they can leave their generation/lineage in the future also. Sometimes multiple forms/versions of a gene are produced by a separate mutation process. These multiple forms/versions of genes are called Polymorphic Genes .

About 99% of all humans have only one form/version of the gene! A polymorphic gene is a very nice type of gene; Because different forms/versions of some polymorphic/ polymorphic genes are partially responsible for differences in human behavior and mental processes.

For example; Let each polymorphic gene affecting eye color be A from the father and B from the mother. Although 3 types of genes are known to play a role in determining eye color; To simplify our example, however, let’s consider the genes determining blue and brown eye color; The genes that are located in the 15th pair of chromosomes! For example, children are lucky to receive all versions of polymorphic genes from each parent! Because of this, there is considerable variation in genes between children!

For example, sons may carry two copies of a version of a gene from each parent; Which I will call 15A. Again, daughters may inherit the 15B version of the gene from either parent. As a result there will be no genetic similarity between these brothers and sisters. As a result, one person’s eye color will be blue and another person’s eye color will be brown.

Dominant and Recessive Genes :

Considering the example of eye color above, whether the eye color will be brown or blue depends on which gene is more dominant! If the eye color is brown, it will be said that; The gene coding of brown color has dominated the gene coding of blue color ! On the other hand, the gene code of blue color will be called latent gene.

When a dominant gene is present, it manifests its symptoms. On the other hand, recessive genes are expressed immediately; When only recessive genes come from both parents and where dominant genes are not present.

Polygenic Traits :

A few aspects of genetic inheritance/heredity are discussed in this context. Although traits such as eye color and body height are controlled by 3 or 4 genes; But other traits are controlled by many more genes.

These different number of genes controlling symptoms are called polygenic traits . These polygenic traits are as important as other behavioral traits, such as intellectual traits or personality traits.

X and Y Chromosomes and Sex :

Human behavior and mental processes are influenced by another process called gender! In the language of biology, X and Y chromosomes are considered as sex determining chromosomes! Males have an X and a Y chromosome as sex determiners; Girls, on the other hand, have both X chromosomes as sex-determiners.

This chromosome undoubtedly creates physical differences between men and women! Such as the presence of different glands, differences in child rearing, etc.! For this reason, despite having the same type of genes between men and women, differences in their behavior are seen due to gender differences.

Genes and Behavior :

How is our physical life so influenced by the DNA deep within our body cells?
This is possible because; Genes code the synthesis of specific proteins in our cells! These proteins make up the structure and organs of our body. When neurons and endocrine glands are formed from cells made of proteins of different components; Then their structure is also operated differently.

Some genes, for example, determine the structure of proteins that guide the axons of neurons. In this way, genes affect the activity of neurons! So that indirectly affects our behavior.

Similarly, genes also control the structure and function of our endocrine glands. As a result; Hormones and neuropeptides are secreted from the endocrine glands for the function of neurons and other organs and influence our behavior.

Genes not only influence our psychosocial behavior by shaping neurons and endocrine glands but also our physical characteristics like height, weight, hair and skin color .

Nurture : Environmental Influence :

Although human heredity has an important influence on his behavior and mental thinking; The experience of his environment also plays an important role in his behavior. We are not strongly influenced by our genes at all! Sometimes the physical qualities are also specially influenced by various elements of the environment.

For example; Although physical height is genetically determined; Since World War II, the average height of people in some countries can be increased by up to 3 inches through nutrition and treatment! Heredity and environmental experiences always work together to influence our psychological qualities.

Physical Environments :

When we talk about the environment in the formation of our life, both material / material ( Physical Environments) environment and psychological environment are mentioned! A factor like water and air pollution is taken into consideration; Such environments and elements have a special influence on human behavior and thinking.

For example; Studies have shown that zinc, mercury, lead, and other heavy metals mixed with the blood have reduced neural activity and intelligence in children! The child of a woman who drinks alcohol during pregnancy has been found to be disruptive and aggressive! So it can be said that physical environments like chemicals affect our behavior and mental thoughts in a special way.

Social Environments :

People are undoubtedly influenced by the social environment! Our parents, children, neighbors all influence our behavior! The language we speak, the food we eat are all influenced by others!

For example; Our parents, children, friends, neighbors are all influenced by the belief that; When a teenager smokes cigarettes , he will suffer the consequences of the health risks caused by smoking.

Culture, Ethnicity and Identity :

The society, culture and ethnicity to which we belong from the very beginning influences our behavior; and makes each one distinct from the other. However, it is not possible to fully understand people without knowing their cultural norms, gender and ethnic identity.

A nation’s culture is defined by its behavior, beliefs and values. People’s culture includes their language, food habits and moral beliefs. So it can be said that culture, race and identity have a special influence on our behavior and mental thinking.