As the years go by, the hair turns gray, wrinkles appear, the breasts sag, the knees ache and the memory begins to fail. The effects of aging are scary, and it is easy to presume that once we reach maturity, all we can do is deteriorate. We idealize youth as the stage in which biology works in our favor; we see the young as enthusiastic and full of life, and the old as weak and miserable. However, the world is full of sad young people and happy senior citizens. Beyond the difficulties that each group faces in their own environment, it turns out that biology does not treat older people as badly as it might seem.
As we get older, we process emotions differently. Basically, throughout our adult lives we experience negative emotions less frequently, until they stabilize around the age of sixty, while positive emotions remain constant. This phenomenon, known as the positivity effect, has been widely demonstrated by science, especially in aspects such as memory or attention.
One example is provided by a study published in 2003 by scientists from the University of California, Santa Cruz. Two images of the same person’s face appeared on a screen; one showing a neutral expression and the other showing happiness, anger or sadness. The two images would then disappear and a small gray dot would appear in the location of one of the faces. Each participant had to indicate, by pressing a button as quickly as possible, whether the dot had appeared on the right or on the left. Older people took longer to press the button when the dot appeared on the side of the angry or sad faces than when it appeared on the side of the happy faces, denoting that they tended to focus more attention on the positive stimuli. The young participants did not show this bias.
Similarly, another study showed that young adults and older adults do not look at all features equally when choosing a product. Participants were shown a graph with information about several car models, such as gasoline consumption, and then they were asked which one they would choose. Older adults spent significantly more time analyzing the advantages of each car than the disadvantages, compared to the young.
Conclusive studies have also been carried out regarding memory. In one of them, participants had to look at 32 different images successively displayed on a screen for two seconds each. Some showed positive scenes, such as a smiling family embracing each other; other images were sad, such as a funeral; and others showed emotionless objects. Next, participants had to describe as many images as they could remember. Older people recalled almost twice as many happy images as sad ones, while the memory of the young ones was not affected by the emotion shown.
Explaining the positivity effect is not an easy task. Since the amygdala is an important part of the brain in processing negative emotions, one could hypothesize that its deterioration is the cause of this effect; however, this does not seem to be the case, as it has been shown that the amygdala is hardly affected by age. Rather, recent evidence indicates that it is not so much a consequence of deterioration as it is an adaptation.
Thus, in order to understand the positivity effect, we have no choice but to look at other primates and animals. A direct consequence of this effect is that older people prioritize valuable social relationships that provide them with positive experiences and tend to have fewer interpersonal conflicts. These characteristics can be easily studied in other species, so we can verify experimentally if the tendency to reduce negative emotions with age is exclusive to humans or not.
Interestingly, the opposite occurs frequently among other primates: as an individual ages, a bias toward negativity appears. This has been documented in capuchins, lemurs and numerous species of monkeys in Africa and Asia. For example, field studies show that, in several macaque species, older individuals devote less time to social behaviors like grooming their mates, but start fights just as often as the younger ones.
A very human oddity
Cayo Santiago is an island in Puerto Rico where scientists study the rhesus macaques, which were artificially introduced there in 1938. The semi-natural conditions in which these monkeys live allow researchers to carry out experiments that would be very complicated elsewhere. In a study published in 2018, they wanted to see if, like humans, old macaques paid less attention than the young ones towards negative stimuli. A researcher would approach a macaque, show it a photo of another individual displaying a neutral or threatening emotion and measure the time the subject looked at it. The results were contrary to those obtained with humans: the old paid more attention to the threatening faces than the young.
Therefore, more than an intrinsic consequence of primate aging, the positivity effect in the elderly seems to be a rarity. Still, humans are not the only exceptions, because in this respect chimpanzees are just like us: older individuals have milder personalities, are less involved in aggression and display the same level of social behaviors.
Why do chimpanzees reduce aggression as they age and other primates do not? The answer might be found in the type of social organization. In a large number of primate species, it has been documented that older individuals reduce their social network, prioritizing the relationships of greater trust. Chimpanzees live in fission-fusion societies, where individuals within the same group divide into small subgroups for a certain period of time, which means that they have more opportunities than other primates to get away from potential enemies.
Only in recent years has the effect of positivity started to be studied in more species of animals. In 2019, the first study addressing this issue with dogs was published. They found that older individuals took longer to react to the sound of human crying than younger individuals, something that did not happen with the sound of laughter. Therefore, as they age, dogs might also show a tendency similar to ours.
Still, it is necessary to expand the number of species studied in order to have a clear picture of the issue and to understand why humans tend to diminish negative emotions with age. In the meantime, we will have to settle for knowing that happiness can simply be a matter of time.
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