Natural Selection
In 1859, Charles Darwin published The Origin of Species, a book in which he proposed an evolutionary process to explain the diversity of life as well as the reasons behind animals' apparent predetermined behavior. This process is called natural selection. According to this creed, inherited traits that contribute most to survival and reproduction are more likely to be passed on to the next generation. Every member of a species has an innate drive to help its genes survive in the future. Over time, mutations (random errors in gene replication) cause genetic diversity.
Today, nearly 150 years later, natural selection and its cousin, evolution, remain the underlying principals of biology. These concepts have had a great influence on certain perspectives of psychology as well. Many psychologists believe that human behavior is in great part a result of our evolutionary past.
A study (Buss, 1994b) surveying the mating preferences of 10,047 people in 37 countries found that: Men everywhere prefer attractive physical features suggesting youth and good health (and hence, reproductive potential). Women prefer men with resources and social status (men that would make good providers). According to evolutionary psychologists, these gender differences are the result of natural selection favoring those who could potentially pass their genes on.
Nurture
There is a lot of evidence to support the idea that genes influence our behavior. It is estimated that genetic influence explains approximately 45% of the variations in our personality traits. Parental influence, often thought to be a major factor in the development of children and adolescents, accounts for an estimated 10% of personality differences, though it can have a greater effect on one's values and beliefs. It is quite apparent that there are other factors that influence behavior.
Prenatal
Even in the womb, nurture varies among individuals. The nutrition received and exposure to any toxic substances varies among embryos, depending on the mothers' actions. This is even true of identical twins in the womb. Prenatal nurture is the earliest example of development differences.
Early Life Experience
Experience helps develop the brain's neural connections. This process is not limited to childhood; throughout life our neural tissue changes in response to different stimuli. Recent studies in brain plasticity show that continuing to learn new things throughout adulthood can employ the brain's ability to create new neural connections. This can alter the brain's chemical and hormonal activity, which plays a great role in mood and emotion.
Normal levels of stimulation are especially important during infancy and early childhood. During these years, new experiences activate and preserve neural connections that might otherwise become inactive. The old saying that a person's personality is shaped within the first ten years of living is not quite conclusive from research. However, various studies show that infants and children from impoverished environments score consistently different on tests of perception and emotional stability than those who have received regular amounts of stimulation and care.
Peer Influence
Human beings are designed to be social animals. We find ourselves in groups during many stages of our lives - family, school, work, etc. Constant interaction with other people is bound to affect one's behavior to some degree. Research shows that children, adolescents, and sometimes adults are extremely sensitive and responsive to influence from their peers.
Adolescence is a time for social and cognitive development, a crucial period of solidifying one's identity. In the search to define the self, adolescents usually choose the company of others similar to themselves in age, appearance, values, and/or interests. Therefore, an adolescent has more in common with his/her peers than his/her parents. This is not to suggest that parents have absolutely no influence on their children's behavior, but think back to when you were a teenager. If your parents said one thing was cool and your friends said another, with whom would you have been more likely to agree?
Culture
Culture is defined as the behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted from one generation to the next. Culture is often, though not necessarily always, given boundaries by ethnicity or geography. Simply put, people from different places sometimes grow up and live differently from one another. Psychologists and anthropologists alike often suggest that one's values and personality traits are heavily influenced by culture.
Every cultural group evolves its own norms - understood rules defining what is acceptable and expected. This can have a great impact on a member's behavior. For example, in many other cultures nudity is not a taboo and people hold normal conversations in their birthday suits, whereas in most of the U.S. many people wouldn't be able to converse with someone in the nude without laughing, being appalled, or being aroused.
Cultures vary in many ways, including child-rearing practices. There are many cultures in which infants receive less attention than we typically give to ours, and others in which children begin to work and help provide for their families before their age is in the double digits. With the emphasis on early life experience already discussed, it is easy to see how learned culture might help shape a person's behavior.
