Personality changes as people age.

WASHINGTON — Do peoples’ personalities change after 30? They can, according to researchers who examined 132,515 adults age 21-60 on the personality traits known as the “Big Five”: conscientiousness, agreeableness, neuroticism, openness and extraversion. These findings are reported in the May issue of the Journal of Personality and Social Psychology, published by the American Psychological Association (APA).

From this large sample of volunteers recruited and examined over the Internet, lead researchers Sanjay Srivastava, Ph.D., and Oliver P. John, Ph.D., working at the University of California at Berkeley, found that certain changes do occur in middle adulthood. Conscientiousness increased throughout the age range studied, with the biggest increases in a person’s 20s; this trait is defined as being organized, planful, and disciplined, and past research has linked it to work performance and work commitments. Agreeableness increased the most during a person’s 30s; this trait is defined as being warm, generous, and helpful, and has been linked to relationships and to prosocial behavior. Neuroticism declined with age for women but did not decline for men; this trait is defined in people who worry and are emotionally unstable. It has been linked to depression and other mental health problems. Openness showed small declines with age for both men and women. Finally, extraversion declined for women but did not show changes in men.

Both neuroticism and extraversion scores were higher for younger women than for younger men. But for both of these traits – and most strikingly for neuroticism – the apparent sex differences diminished with age.

Of the 132,515 participants, 54 percent were female, all lived in the U.S. or Canada, 86% were White and 14% were Asian, Black, Latino or Middle Eastern. A subset of the sample – 42,578 – were asked about their socioeconomic status. Of these participants, 405 (1%) said they were poor, 7,614 (18%) said they were working class, 23,024 (54%) said they were middle class and 10,718 (25%) said they were upper-middle class.

This study contradicts an often cited view that personality traits are genetically programmed to stop changing by early adulthood. There is considerable evidence against it, say the authors. In the study, “average levels of personality traits changed gradually but systematically throughout the lifespan, sometimes even more after age 30 than before. Increasing conscientiousness and agreeableness and decreasing neuroticism in adulthood may indicate increasing maturity – people becoming on the average better adapted as they get older, well into middle age.”

The full paper is available online in PDF format (i.e. you will need Acrobat Reader or an equivalent PDF viewer to read it). Page 7 of the PDF has a nice set of graphs that plot the measured personality characteristics as a function of age.

The really interesting question that this paper does not answer is what causes the personality changes as people age? Does experience with life cause most of the changes? That sounds plausible. But it also seems plausible that physical aging processes cause some parts of the mind to slow down or change in function in ways that change personality.

It is important to discover the causes of personality changes with age because eventually it will become possible to reverse the aging process. Will doing so make people less agreeable? Will it make them more prone to commit violent crimes? Will the reversal of the declining levels of hormones that happens with age make some people more inclined to start fights and do physical damage to others? That sounds only too plausible.

One problem with this study is that it was not longitudinal. The paper provides good arguments for why the researchers believe that there was not sampling bias of types of internet users as a function of age. They probably are reporting a real phenomenon.

What is needed are studies that try to get at the question of how much physical aging processes cause personality changes and which specific physical age-related changes cause which specific changes in personality and behavior.

There are ways this question can be approached. First off, people do not all age at the same rate. Physical measures of aging could be done along with personality measures for people of the same age. Personality changes might be found to happen more rapidly in people whose aging biomarkers are more advanced than those same biomarkers are for others of the same age who have personalities which are more like younger personalities. Blood hormone levels, insulin resistance, different cognitive abilities (since they do not all decline at the same rate), oxidative stress indicators, bone density, and many other biomarkers could be used. But unfortunately such a study would be orders of magnitude more expensive than an internet personality test study.

When it becomes possible to reverse the aging process then people will feel more energetic and will experience higher levels of hormones and more active minds. Their sexual drives will increase and their physical strength will increase. It seems likely that some of these changes will cause an increase in the rate at which people commit crimes. Murder, rape, and other violent crimes will likely rise and it seems likely that even non-violent white collar crime rates will rise as well.

To get a sense of just how much higher crime rates are for youths and early adults see this excerpt from the US FBI 1995 Uniform Crime Report.

Offenses involving only offenders under 18 years of age accounted for 22 percent of the overall Crime Index clearances, 14 percent of the violent crime clearances, and 25 percent of the property crime clearances.

Keep in mind that while that represents a fairly large age bracket the pre-teens are committing very few of those crimes. To get a sense of just how important age is as a factor in violent crime check out this chart of age-specific murder arrest rates. After peaking around the age of 19 murder arrests per 100,000 population drop by more than an order of magnitude by the late 40s and continue to drop by another factor of 3 by the early 60s.

We face a basic question about when it becomes possible to reverse the aging process: how much will the rates of various types of crime rise?

I won't go into it here but the story about crime and age is considerably more complcated for other types of crime. Some criminologists think that criminal personalities just shift their criminal activities toward less physically strenuous activities as they get older. Also, they learn skills that let them carry out other forms of criminal activity.

Still, an aged person made youthful by future biotechnology will have a greater general level of energy, greater strength, greater sexual drive, and stronger desires and appetites. The stronger drives and desires will be more likely to overpower inhibitions. The inability to resist impulses is a quality which many theorists think characterize the criminal mind. Well, a person who experiences an increase in the frequency and size of the impulses and of the ability to act upon them will act on them more often.