研究显示，人类的天性就是爱撒谎，而且下午比上午更爱撒谎。哈佛大学研究发现，人类每天下午随着身体逐渐疲惫，自控能力也会下降，更容易不由自主地撒谎。

研究者还发现，平时越老实的人越容易在下午受到意志力脆弱的影响，开始变得爱撒谎。而与之相反，平时就对撒谎无压力的人比较不容易在下午恶化，因为他们平时自控能力就相对较差，反而显得上下午差别不大。

People are more likely to lie or cheat during the afternoon because self control diminishes during the day, according to researchers.

Volunteers taking part in two experiments where they could benefit by cheating were more likely to do so if the tests took place after midday, researchers found.

The findings back up previous studies which have shown that our capacity for self-control declines during the day, due to tiredness and repeatedly making decisions.

Psychologists from Harvard University first showed a group of volunteers various patterns of dots on a computer screen, asking them to decide whether there were more dots on the left or the right hand side.

Instead of being rewarded for getting the answer right, the participants were paid based on which side they chose, earning ten times as much for choosing the right hand side as the left.

People who were tested after midday were significantly more likely to select the right hand side, even if there were clearly more dots on the left, than those who took part during the morning.

In a second test, participants were shown a series of word fragments, such as "--ral" and "e---c--" and asked which words they associated with them.

In morning experiments, participants were more likely to form the words "moral" and "ethical" while during the afternoon the words "coral" and "effects" were most common.

Further tests conducted online showed that people were more likely to send dishonest messages or claim to have solved an unsolvable problem in the afternoon than the morning.

Writing the Psychological Science journal, the researchers said the difference was particularly pronounced in people with higher ethical standards, who always behaved morally during the morning but slipped during the afternoon.

In contrast, those who were able to "morally disengage", or behave unethically without feeling guilty, were prone to cheating whatever the time of day.

Dr Maryam Kouchaki, one of the lead authors, said: "Unfortunately, the most honest people, such as those less likely to morally disengage, may be the most susceptible to the negative consequences associated with the morning morality effect."

The findings could be relevant to organisations who should be more vigilant about the behaviour of customers and employees during the afternoon, she added. “Our findings suggest that mere time of day can lead to a systematic failure of good people to act morally.”

（中国日报网英语点津 陈丹妮 编辑）