A baby bawling at night can strain its parents’ relationship to breaking point.

But far from being an unfortunate side effect, researchers claim it is the biological reason for the infant’s crying.

Babies are programmed to monopolise their mother’s attention, say Harvard University scientists – and making parents too tired for a romantic night together is a way of preventing the arrival of a new sibling.

The report claims breastfeeding at night also extends a mother’s post-birth infertility, known as amenorrhoea.

Author Professor David Haig said: ‘Night waking increases in the second half of the first year of infant life and is more pronounced for breastfed babies.’

He said this suggests waking at night to suckle is an ‘adaptation of infants to extend their mother’s amenorrhoea, thus delaying the birth of a younger sibling and enhancing infant survival’.

The evolutionary biologist added: ‘Natural selection will have preserved … behaviours of infants that suppress ovarian function in the mothers because infants have benefited from delay of the next birth. Maternal fatigue can be seen as an integral part of an infant’s strategy to extend the IBI (inter-birth interval).’

His study adds: 'Short delays until the birth of a younger sib are associated with increased mortality of infants and toddlers, especially in environments of resource scarcity and rampant infectious disease.

'More frequent and more intense nursing, especially at night, [is] associated with prolonged infertility.

'Natural selection will have preserved suckling and sleeping behaviours of infants that suppress ovarian function in the mothers because infants have benefited from delay of the next birth.

'Maternal fatigue can be seen as an integral part of an infant’s strategy to extend the IBI.

'Breastfeeding has many virtues but, for many mothers, a good night’s sleep is not counted among them.'

Siobhan Freegard, founder of Britain’s biggest parenting website Netmums said: 'The arrival of a new baby tests even the strongest relationships, so parents will be amused to find out the exhaustion and sleepless nights are all part of Mother Nature’s plan.

'Spacing out siblings would give the mother more time to recover from the birth and make young children more independent boosting their chances of survival, so this research makes perfect sense.

'The last thing most frazzled new mums feel like is trying to conceive another child – and now they have the excuse that a limited love life in the first year is what nature wants.' 

A recent Japanese study claimed babies can fake crying to get the attention of their mother.

By Daily Mail Reporter

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