It's official. Babies cry to stop us having more babies.

The reason new babies cry so much at night has finally been revealed, and no, it isn’t because they haven’t read the routine.

Every mother has spent countless hours trying to figure out why their baby is crying. We’re presented with so many theories and explanations and it all comes down to some kind of responsibility on our part:

They are hungry;

They are tired;

They are over-stimulated;

They are absorbing your stress and tension;

They are releasing emotion;

They have a dirty nappy;

They are used to sleeping during the day when being rocked in their mother’s tummies therefore are used to being awake at night;

They communicate through crying because they can’t speak yet.

Researchers at Harvard University claim the real reason babies cry frequently at night is to stop their parents from producing competitive offspring. This increases their chance survival.

Professor David Haig from Harvard University presented his theory in the May edition of the journal Evolution, Medicine, and Public Health. He says newborns wake every two to four hours for the first eight weeks and every four to six hours after that so they increase the frequency of breastfeeding which naturally prevents ovulation.

So, it's a bit more primal and sophisticated than just interrupting their parents every time they have try and have sex. It's also not about making their parents fatigued so they can't be bothered, although that's just as effective. Survival instincts are apparently programmed into our babies until they are stronger and healthier and no longer feel the need to prevent competitive sibs.

Professor Haig explains, “Waking at night to suckle is an adaptation of infants to extend their mothers’ lactational amenorrhea (non-ovulation) thus delaying the birth of a younger sibling and enhancing infant survival."

“Natural selection will have preserved suckling and sleeping behaviours of infants that suppress ovarian function in mothers because infants have benefited from delay of the next birth. Maximal night waking can be conjectured to overlap with the greatest benefits of contraceptive suckling."

Wow, 'contraceptive suckling'. We are a parenting website and this is the first time we have heard breastfeeding referred to like this. Anyway...

He explains that despite the fact babies are more likely to survive in the modern world these sorts of behaviours remain part of our biological heritage and continue despite improvements in rates of infant survival.

So next time you're feeling frustrated with your baby who is STILL crying despite being feed, changed and cuddled, perhaps sit down in a rocker and whisper reassurances into their little ears that producing a sibling is the last thing you and daddy are thinking of right now, thank you very much.

Do you think this is a good theory as to why babies cry and cry and cry at night?