Good news for parents of young babies who are dismayed to be greeted with a flood of tears when they return home from work: it is not your fault.
A new study suggests that infants in the first few months of their life hit a peak of bad temper in the evenings as a result of the interaction between their natural circadian rhythms and developing nocturnal sleep patterns.
Peter Totterdell, a senior research fellow at the University of Sheffield, said: "Early evening, when working parents are most likely to come home, is the least rewarding time for child care."
He told the British Psychological Society's meeting this week that the effect naturally dies away as the baby learns to sleep more at night.
He said the evening temper tantrums were not caused by changes in the ability of the gastro-intestinal system to digest food, over-stimulation at the end of the day and certainly
not as a result of parenting.
Dr Totterdell's research, based on observations of his daughter Emma, showed there was a decline in the circadian rhythm of unhappiness that was matched by an increase in the circadian rhythm of sleep.
As the child develops its nocturnal sleep patterns, outside influences suppress the natural inclination to
bad temper in the evenings.
"With a newborn baby you're seeing the raw mood rhythm being expressed, but as its body clock and its sleep-wake cycle get in sync, the effect tends to disappear," said Dr Totterdell.
"The good news is it takes the blame away from the parent. The bad news is most parents are going to go through this to a greater or lesser degree."