Meet your new classmates, Tom and Jerry. When you are sad, Jerry is the type of friend that will come up to you and hug you. Tom, on the other hand, is more likely to laugh at you and make you feel silly for feeling sad. Tom and Jerry think and behave differently; that is, they have different personalities. People’s personalities are made up of several personality traits. Some of these personality traits are generally seen as positive (so-called “light” traits) and some are generally seen as negative (so-called “dark” traits), although it is more complicated than that and we all have a mix of both. In this article, we discuss the personalities of Tom and Jerry and the differences and similarities between them. We will also help you to investigate your own personality, to find out if you are more like Tom or Jerry. Lastly, we will talk about how Tom became Tom and how Jerry became Jerry, and whether either of their personalities can change with time.
What Is Personality?
Meet your new classmates, Tom and Jerry. Jerry tends to help his classmates with their homework, share his lunch, and hug his friends when they are sad. Tom tends to laugh at his classmates, call them names, and take their pencils without asking. Is there someone in your school that sounds a lot like Tom or Jerry? It is likely that you can think of kids that you would say are often helpful, fair, or kind, and others that you would say are sometimes selfish, rude or mean. These words are examples used to describe people’s personalities. Personality is all about how a person thinks, feels, and behaves throughout their life. The words that we use to describe personality are referred to as personality traits . Learning about personality helps us understand our own and other people’s actions and feelings. Scientists have observed that some personality traits, such as being helpful or sweet, are related to being happier in life. Other traits, such as being rude or mean, are related to being less happy in life. Psychologists (scientists who study the ways that people think, feel, and behave) decided to group some of these personality traits based on how they can influence our lives. They called the traits that influence life positively “light” and those that influence life negatively “dark.” Scientists love to divide things into categories such as light and dark. By creating these categories, scientists are better able to describe someone’s personality in detail. For example, if you had to describe what you had for lunch today, describing it using big categories like “fruit” or “sweets” or specific characteristics like “soft” or “red” makes it so much easier compared to if you only had one or two words to describe your lunch. The same thing holds true for scientists that are trying to understand personality.
The Light Side of Personality
A group of scientists who were interested in understanding people’s strengths and positive qualities discovered three personality traits that they believe reflect the good in people. They called these three traits the Light Triad (Figure 1A) . The Light Triad includes the traits faith in humanity, humanism, and Kantianism. People who have a lot of faith in humanity tend to see the good in people and can forgive and trust others easily. People with a lot of humanism tend to treat other people with kindness and respect (Figure 1B). Lastly, people with a lot of Kantianism are generally honest and do not use others for their benefit. Jerry is a good example of someone who has a lot of Light Triad in his personality. Jerry is nice to all his classmates, he does not lie, and he apologizes when he has hurt someone. There are many advantages to having lots of “lightness” in your personality. For example, scientists have observed that people who are higher on the Light Triad tend to be more accepting of others, more enthusiastic, and even happier with their lives.
The Dark Side of Personality
But what about the people you know who are a little bit like Tom? Such people might not care so much about the feelings of others and may find it hard to understand how their actions make others feel. They generally do not feel badly when they harm others in some way, and they often do not feel the need to apologize for their actions. People like Tom frequently do not believe that other people in the world are good or nice. Scientists have grouped three of these Tom-like traits and refer to them as the Dark Triad: narcissism, Machiavellianism, and psychopathy (Figure 2A) . People with lots of narcissism usually try to attract a lot of attention to themselves. They want others to look up to them and want everything to be about them (Figure 2B). People that have lots of Machiavellianism in their personalities tend to be manipulative and try to make everything go their way. Finally, people with lots of psychopathy may hurt others and may care very little about how other people feel about their actions or behavior. However, not everything about these dark traits is bad. Dark personality traits can be helpful, too! For example, Tom’s narcissism pushes him to do his best in school and to get good grades, in the hope that the other kids will look up to him as a result.
Measuring the Light and Dark Sides of Personality
Are you curious about your personality? To measure light and dark personality traits, psychologists may ask people how much they recognize themselves in certain statements.
Examples of light personality traits  are:
- “I am quick to forgive people who have hurt me”
- “I think people are mostly good”
- “I tend to applaud the successes of other people”
Examples of dark personality traits  are:
- “Many group activities tend to be dull without me”
- “You should wait for the right time to get back at people”
- “I’ll say anything to get what I want”
Jerry would recognize himself most in the first three statements, Tom feels more at home reading the last three statements. On a scale from Tom to Jerry, how much do you recognize yourself in each of these statements?
Where Do Our Personality Traits Come From?
But where do light and dark personality traits come from in the first place? Personality traits are influenced by two factors: genes and environment and, more importantly, the way these two interact with each other. Let us first talk about genes. You might have noticed that you have some similarities with your parents, siblings, or even grandparents. You might look alike, behave similarly, or like the same types of activities. Similarities shared with family members are partly due to genes. In terms of the second factor, environment, think about where you live, the interactions with your parents and friends, and all the things you have already experienced in your life. Where we spend our time and the people we spend it with influence how we feel or think about things.
But how exactly do genes and the environment influence each other? Scientists refer to this as gene-environment interactions (Figure 3) . To understand gene-environment interactions, let us consider how likely it is for you to become a professional basketball player. Imagine that you are naturally tall and athletic, and that you have high endurance. These characteristics have to do with your genes. Now imagine that, on top of these traits, your parents are always encouraging you to work hard, push yourself, and not give up when things get hard. These elements are part of your environment. Either your genes or your environment alone could increase your chances of becoming a professional basketball player, but if these two things come together, your chances increase much more!
Stability of Personality
For a long time, scientists thought that personalities were set in stone and would not change over time. More recently, they have changed their minds—they have discovered that, while a lot of the personality remains stable, even as we grow older, personality can change a little bit . For instance, scientists have discovered that, as we grow older, our dark traits tend to become less dominant. In other words, as we grow older, our hair turns gray and so do our personalities!
People possess many personality traits. Some personality traits are viewed more positively, the so-called “light” traits, while others are viewed more negatively, the so-called “dark” traits. The question is not whether Tom, Jerry, you, or I have light or dark personality traits, but rather, how many light and dark traits we have in our personalities and how much of each of these traits we have. Just like everyone’s fingerprints are unique, so is everyone’s personality: everyone has a unique mix of personality traits in different quantities! The interaction between our genes and our environments influences what our personalities are like. And, as we grow older, our personalities may change a little bit. However, it is safe to say that all of us have a little bit of Tom and a little bit of Jerry as part of our personalities.
Personality: ↑ Someone’s way of thinking, feeling, and behaving.
Personality Traits: ↑ Personality traits are the unique ingredients that make us who we are. They help explain why people act the way they do and why we are all a little different.
Psychologist: ↑ Someone who studies why people think, feel, and behave the way they do. They help us learn more about our thoughts and feelings and when we need someone to talk to.
Light Triad: ↑ Three personality traits that are seen as rather desirable. These traits include seeing the good in others, caring a lot about others, and not using others for their benefit.
Dark Triad: ↑ Three personality traits that are seen as rather undesirable. These traits include not caring as much about how others feel and maybe even doing things that could hurt others.
Genes: ↑ Pieces of DNA that carry information, including information about our personality traits, that is passed from parents to children.
Gene-environment Interactions: ↑ A given set of genes may lead to different traits, depending on environmental factors like where a person lives and who they spend time with. Both factors influence each other.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
 ↑ Ashton, M. C., and Lee, K. 2001. A theoretical basis for the major dimensions of personality. Eur. J. Personal. 15:327–53. doi: 10.1002/per.417
 ↑ Kaufman, S. B., Yaden, D. B., Hyde, E., and Tsukayama, E. 2019. The Light vs. Dark Triad of personality: contrasting two very different profiles of human nature. Front. Psychol. 10:467. doi: 10.3389/fpsyg.2019.00467
 ↑ Jones, D. N., and Paulhus, D. L. 2014. Introducing the short Dark Triad (SD3): a brief measure of dark personality traits. Assessment. 21:28–41. doi: 10.1177/1073191113514105
 ↑ Krueger, R. F., South, S., Johnson, W., and Iacono, W. 2008. The heritability of personality is not always 50%: gene-environment interactions and correlations between personality and parenting. J. Pers. 76:1485–522. doi: 10.1111/j.1467-6494.2008.00529.x
 ↑ Costa, P. T., McCrae, R. R., and Löckenhoff, C. E. 2019. Personality across the life span. Annu. Rev. Psychol. 70:423–48. doi: 10.1146/annurev-psych-010418-103244