Human Diversity

Similarity vs distinctiveness

  • Asks are we as a species more alike or more different? 

Evidence for similarity:

  • All humans share a common biological heritage. More or less our biological inheritances are identical. I.e. We have two eyes, two ears, and if we are cut, we bleed. We as a species have share behavioral tendencies. Our behavior occurs through the same mechanisms.

Evidence for distinctiveness:

  • Different humans have different appearances, sounds, and psychological experiences (i.e. some people have calm dispositions and some people have anxious dispositions)

  • Although there are many similarities across a species, and the similarities outway the differences, differences are more likely to attract attention

Behavior genetics

What is behavior genetics?

  • The study of the relative influences of heredity and environment on behavior.

  • Our heredity includes our genes. Our heredity influences our phenotypes.

  • Our environment includes every nongenetic influence.

How to study behavior genetics

  • Two types of experiments - both provided by nature.

  • In one, the behavioral geneticists keep the home environment constant while allowing the heredity to vary. Used to assess the influence of genes on behavior.

  • Nature allows heredity to be kept constant while the home environment is allowed to vary. Used to assess the influence of the environment on behavior.

Twins reared together:

  • Identical twins tend to be much more similar on measures of personality than fraternal twins.

  • Identical twins tend to much more similar to each other on measures of social 

  • Anecdotal evidence: the Jim twins - identical twins who were separated one month after birth. Were both adopted out into blue collar families without any knowledge of each other. Nevertheless, both Jims had wives named Linda. Both Jims divorced and got remarried to women named Betty. Both left love notes around the house for their wives, both had sons named James Allen. Both had dogs named Toy. Both enjoyed woodworking and craftsmanship, drove a chevy, and both drank miller light beer.

  • Scientific evidence: Identical twins who are reared together tend to be more similar than those reared apart. This underscores the importance of the environment. Identical twins who are reared apart tend to be more similar than fraternal twins reared apart.

Adoption studies

Genetic vs environmental relatives:

  • Through adoption, two groups of individuals are selected, one group is genetic relatives, and the other group is environmental relatives (i.e. adoptive family). People who grow up together do not much resemble one another in their personalities. Adoptees are more similar to their biological parents than they are to their adoptive parents. Adoptive parents do influence their adoptees on things such as attitude, manners, religion, and politics.

Heritability: The extent to which variations amongst individuals can be attributed to their varying genes.

Evolutionary psychology

What is evolutionary psychology?

  • The study of the evolution of behavior and the mind. 

  • All of our psychological experiences are evolved because they have been shown to be changed as necessary over time.

Natural selection

Philosophical tenets:

  • Offspring compete with one another for survival.

  • The chances of reproduction and survival are enhanced or diminished by certain biological and behavioral variations across a species.

  • Offspring who survive are more likely to reproduce and in doing so pass on genes to ensuing generations of offspring

  • Survival of the fittest results in changes to population characteristics over time.

Evolutionary psychology and human sexuality

Men and women tend to be highly similar and this similarity is due to mens and womens having faced similar challenges and having adapted in similar ways.

  • Gender difference in sexuality: Men are more likely to initiate sexual activity than women.

  • Average looking research assistants walked across campus. In walking across campus, the research assistant would walk up to someone of the opposite sex and would say “I've noticed you around campus and you’re very attractive. Would you like to go to bed with me.” 0% of women said yes and 75% of men said yes. 

  • Gender differences in views on sexuality: women tend to view sex more in relationship terms, the emotional connection. Men tend to view sex more in recreational terms. 

  • Gender difference in mating preferences: males on average tend to prefer women with smooth skin and a youthful shape. Men also on average prefer women who are at a “prime age". Women on average prefer men who are willing to commit to them and father offspring. They also tend to prefer mature, dominant, and confident men. According to evolutionary psychology, these preferences have occurred through natural selection.

Gender development

Gender similarity: 

  • With the exception of one chromosome, men and women are highly similar in their gender make up. Men and women are similar in their level of intelligence, vocabulary, and happiness.

Gender differences:

Physical differences: 

  • Women tend to enter puberty two years before men. 

  • Women tend to live 5 years longer than men on average. 

  • Women tend to carry more body fat, less muscle mass, and 5 inches shorter. 

Psychological differences:

  • Women are more prone to depression, anxiety, and eating disorders

  • Men are more prone to alcoholism and suicide

  • As children, men are more likely to be diagnosed with autism, color blindness, and ADHD

  • As adults, men are more likely to be diagnosed with antisocial personality disorder 

Social differences:

  • Men admit to and show more aggression. 

  • Men are more socially dominant

  • Women tend to be more interdependent and socially connected

  • Women tend to better understand others' emotions.

Culture and human diversity

The beneficial influence of culture:

Culture refers to the behaviors, ideas, attitudes, values, and traditions that are shared by a group of people. 

  • Culture facilitates our species survival and reproduction. Enables social and economic systems that give an adaptive advantage.

  • Culture allows for preservation of innovation.

Different types of culture:

Cultures vary to the extent of which cultures give priority to personal or group identity.

  • Individualist: value personal achievements. Emphasis on individual freedoms and priorities. Relationships are oftentimes temporary and casual, “how can I use this person to get ahead?” Identity is defined in terms of personal traits. People tend to strive for personal control and individual achievement.

  • Collectivist: value is on group goals and solidarity. “How can we work together as a team?” Emphasis is on group norms and customs. Relationships are oftentimes close and enduring. Identity is defined in terms of group membership. There is a tendency to strive to maintain social connections, to fit in, and to perform one's role in society.