This is the 2007 version. Click here for the 2017 chapter 11 table of contents.

Genetic Influences on Personality?

To what extent are personality traits, in fact, genetic traits? If we look at non-human animals, such as dogs, we can see the results of life experiences (for example, a dog that is given lots of love as a puppy will often have a sweet personality) but we can also see breed personalities. Dogs have been selectively bred by humans to produce different breeds with specific characteristics. One result is the emergence of distinct, identifiable personalities in different dog breeds. Afghans are aloof, beagles are irrepressibly friendly, certain sheep dogs are bred to be shy of strangers, and so forth. These are examples of behavioral traits coded in the genes. One could predict that clones would have very similar personalities, and indeed, a manager who worked for Infigen, a biotech company that cloned 193 cattle, said, "These clones have the same personalities...They bellow all the time. They're easygoing, friendly" (Kristof, 2002).

What are examples of breed personalities in dogs? What gave the Freedmans a unique background for their work?

Might humans also have genetically-influenced personality traits? One husband/wife research team, Daniel and Nina Freedman, thought so (Freedman & Freedman, 1985). Daniel raised and trained dogs for a living. Nina was a developmental psychologist. Daniel's ancestors came from Europe, Nina's parents came from China. They noticed big differences in the way their families behaved. For example, Daniel's family was animated around the dinner table, Nina's was quiet. The obvious explanation is that Chinese and American cultures have different rules of conduct at mealtime. But where do the rules come from? The Freedmans started wondering if the difference might be based partly on genetics.

The Freedmans decided to make behavioral comparisons between infants of differing ethnic backgrounds. They figured that newborn infants were still too young to be influenced by culture, so behavioral differences would probably be due to genetic differences. They located pregnant women of European or Chinese ancestry in the San Francisco area. The two groups were matched on such variables as years spent in the United States, quality of prenatal care, and income level. The babies of these mothers were tested soon after birth.

Sure enough, there were big differences in temperament. The American babies cried loudly when angry and were hard to calm. The Chinese babies stopped crying almost immediately when picked up. The American babies turned their heads vigorously if a cloth was placed on the nose. (The Freedmans pointed out this was listed in American pediatric textbooks as the "normal" response.) However, the Chinese babies merely breathed through their mouths when their noses were covered.

Why was it significant to the Freedmans that Navajo babies resembled Chinese babies in behavior?

In further research the Freedmans found striking similarities in the behavior of Chinese and Navajo babies. The Navajo babies, when tested, resembled the Chinese babies in every way, but were unlike the Caucasian babies. This is significant because Navajos are descended from people of Asia who migrated over the land bridge between Alaska and Siberia around 10,000 years ago. One would expect genetically based behavior patterns to be similar in the two groups.

The Freedmans' research by itself would not be enough to prove that temperament is "in the genes." However, there are many sources of evidence that point to the same conclusion. In the 1980s, several personality theorists, such as Buss and Plomin, addressed the genetic basis of personality traits and temperament. By 1987 Plomin (1987) was calling the finding of genetic influences on personality "the single most important finding in behavioral genetics in the last decade."

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