There is more that comes with older age than greying hair and wrinkled skin When humans reach their later years, they favour more established friends and their social circle is reduced.
Now, for what appears to be the first time, scientists have seen the same behaviour in another species. Twenty years of observations of chimpanzees (猩猩) reveal that older males choose to hang out with their long-term friends at the expense of other relationships.
The researchers studied 78, 000 hours of observations made between 1996 and 2016 that followed the social interactions of 21 male chimpanzees between the ages of 15 and 58 years old. They classified the chimps’ relationships depending on the amount of time they sat with others and groomed (梳毛) them. They then rated the various pairings as mutual (相互的) friendships, where both chimps seemed to enjoy the relationship; one-sided friendships, where one chimp was more keen to be friends than the other; and non-friendships, where neither chimp showed interest in the other.
When the scientists looked at the patterns of friendships, they found that the older chimps had more mutual friendships and fewer one-sided friendships than younger chimps. Another feature seen in older humans was also spotted in the chimps. As the males got older, their levels of aggression (挑衅) tailed off, meaning they started fewer fights and tended to intimidate others in their group less often.
The observations have left the researchers puzzled. According to an idea in psychology known as socioemotional selectivity theory, or SST, older humans prefer more positive relationships because they are aware time is running out. But many animal experts argue that chimpanzees lack the human sense of mortality (死亡), suggesting something else is driving the behaviour.
Robin Dunbar, a professor of evolutionary psychology at the University of Oxford, said in humans, the decline in social circles with age is due to declining social motivation to get out and meet people combined by lack of opportunity. In chimpanzees, as older males compete less for mates, they may focus on close, reciprocal (互惠的) relationships with trusted partners, she said.
12. What do older male chimpanzees favour?
A.Old friendships. | B.New bonds. |
C.Greying hair. | D.Wrinkled skin. |
13. How did the researchers draw their conclusion about chimpanzees?
A.By turning to other scientists. |
B.By introducing a new concept. |
C.By forming relationships with them. |
D.By analyzing two decades’ observations. |
14. What does the underlined word “intimidate” in Paragraph 4 mean?
A.Threaten. | B.Motivate. | C.Defend. | D.Accompany. |
15. According to Robin Dunbar, what accounts for declining social circles in chimpanzees?
A.Awareness of time. | B.Less competition for mates. |
C.Low motivation for socialization. | D.Lack of the human sense of mortality. |