If you're wondering why your baby is always crying at night, scientists claim to have found the answer: they want to stop you making a little brother or sister!
Researchers at Harvard University say babies are programmed to monopolise their mother's attention – and making parents too tired for some under-the-duvet action is a way of preventing the arrival of a new sibling.
The report also claims that breastfeeding at night 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'.
He 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."
Japanese researchers studied two babies crying over a period of six months and believe the infants are capable of the clever deception.
Or perhaps these scientists are overthinking this, and babies just cry because they are babies and want their mother's attention and to be fed and cuddled. Just saying.
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