研究顯示，人類的天性就是愛撒謊，而且下午比上午更愛撒謊。哈佛大學研究發現，人類每天下午隨著身體逐漸疲憊，自控能力也會下降，更容易不由自主地撒謊。

研究者還發現，平時越老實的人越容易在下午受到意志力脆弱的影響，開始變得愛撒謊。而與之相反，平時就對撒謊無壓力的人比較不容易在下午惡化，因為他們平時自控能力就相對較差，反而顯得上下午差別不大。

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.”

（中國日報網英語點津 陳丹妮 編輯）