A normal human baby, according to psychologists, will cry about two hours over the course of a day.
A notorious human crybaby, according to her older siblings, parents and the building superintendent, will cry for two hours every two hours, refusing to acknowledge any distinction between crying and other basic infant activities, like "being awake" or "breathing".
Current and former whine enthusiasts, take heart. It turns out that infant crying is not only as natural and justifiable as breathing: the two acts are physically, neurologically, primally intertwined.
Scientists have discovered that the small cluster of brain cells in charge of fast, active respiration also grant a baby animal the power to cry.
Reporting in the Proceedings Of The National Academy Of Sciences, Professor Carmen Birchmeier and Dr Luis Hernandez-Miranda, of the Max Delbruck Centre for Molecular Medicine in Berlin, and their colleagues showed that infant mice stripped of this key node - a mere 17,000 neurons, located in the evolutionarily ancient hindbrain - can breathe slowly and passively, but not vigorously or animatedly.
When they open their mouths to cry, nothing comes out. As a result, their mothers ignore them, and the poorly breathing pups quickly die.
"This was an astonishing finding," Prof Birchmeier said. "The mother could see the pups and smell the pups, but if they didn't vocalise, it was as though they didn't exist." The new study is just one in a series of recent reports that reveal the centrality of crying to infant survival, and how a baby's bawl punches through a cluttered acoustic landscape to demand immediate adult attention.
The sound of an infant's cry arouses a far quicker and stronger response in action-oriented parts of the adult brain than do similarly loud or emotionally laden noises, like a dog barking or a neighbour weeping.
Scientists also have shown that the cries of many infant mammals share a number of basic sonic properties. University of Winnipeg biologist Susan Lingle and her co-workers have conducted field studies in which they broadcast through loudspeakers the amplified creche cries of a panoply of animals, including a baby bat, a baby eland, a sea lion pup, a baby marmot, a kid goat and a domestic kitten.
Sometimes the cry was played as is. Sometimes a single feature - the cry's pitch - was raised or lowered while everything else remained the same. No matter the infantile source of the SOS, the reaction of a mother deer grazing nearby was the same: She would bound at top speed towards the speaker as though to her own fawn in distress.
Deer aren't the only ones to be bamboozled. At a conference on infant wailing held earlier this year in Italy, Dr Lingle played an audio clip of cries from a kid, fawn and baby, and asked the audience which was human.
"The majority got it right," she said, "but many admitted they really weren't sure."
Said Dr Patrick Thomas, curator of mammals at the Bronx Zoo: "When a cheetah cub is separated from its mother, it chirps like a bird."
The cry of a baby kangaroo sounds like a cough.
Researchers are searching for any telltale variations in the cries of human infants that might be used diagnostically to identify conditions like autism long before behavioural symptoms arise.
Dr Stephen Sheinkopf and Dr Barry Lester of Brown University and their colleagues recently showed that environmental factors, too, may subtly shape the sound of a baby's cry by impinging on a gene involved in an infant's response to cortisol, a critical stress hormone.
Harried parents might prefer the scientists focus on a simple translation manual. What is my screaming angel trying to tell me?
Professor Mariano Choliz, a psychologist at the University of Valencia, and his co-workers have made a first-pass attempt to categorise infant cries.
In The Spanish Journal Of Psychology, the researchers described laboratory studies in which infants were subjected to various unpleasant procedures known to elicit different emotional states.
The resulting cries were videotaped and analysed.
To provoke anger, the investigators pinned down the babies' hands or feet and prevented them from moving. To arouse fear, the researchers clapped their hands loudly or dropped a book on the floor. A cry of pain followed "the obligatory vaccination", according to the study.
Prof Choliz found that angry babies tended to keep their eyes half closed, gazing off to the side as they cried. They steadily amped up the volume of vocalised umbrage. Frightened babies, after an initial hesitation and tensing up of the facial muscles, emitted an explosive cry and kept their eyes open and searching the whole time.
Babies pained by a needle prick cried out immediately, at full force, and squeezed their eyes shut. They maintained that expression and volume for the entire crying bout.
The take-home message for parents: If you happen to drop a heavy object on the floor while the paediatrician is pinning down your baby's leg for a shot, your child will be in therapy for life.
That humans and other infant mammals are painfully dependent on their elders for survival is reflected in the distinctive spectrographic contours of a cry. An infant cry is characterised by a simple, clear, fundamental tone and a relatively long, unbroken "melodic structure", as it is perversely called, that falls and rises and falls and tails off in unpredictable ways.
"If a stimulus stays the same, it's easy to tune out," said Dr Katherine S. Young, a psychologist at the University of California, Los Angeles. "But something that changes over time is very difficult to ignore."
Police sirens and other alert sounds mimic this pattern of a slow increase and decrease in pitch, said Dr Young, "because it grabs and holds your attention".
By the look of it, the adult brain is primed to be buttonholed.
Studying both superfast brain scans of healthy volunteers and direct electrode measurements in adult patients who were undergoing neurosurgery for other reasons, Dr Young, with Dr Christine E. Parsons of Aarhus University in Denmark, Professor Morten L. Kringelbach of Oxford University and other colleagues, has tracked the brain's response to the sound of an infant cry.
The researchers found that within 49-thousandths of a second of a recorded cry being played, the periaqueductal grey - an area deep in the midbrain that has long been linked to urgent, do-or-die behaviours - had blazed to attention, twice as fast as it reacted to dozens of other audio clips tested.
The investigators also detected rapid firing in brain regions that check a stimulus for its emotional salience and in motor areas that control movement.
Is this sound important? Yes. Should I do something about it? Absolutely.This spur to caretaking action - this antsy, subliminal desire to resolve the dilemma presented by the wailing infant - could explain why a crying infant on an airplane is especially distressing. Passengers want to help; they can't, and they can't even run away.
In another study, volunteers were asked to play a lab version of the popular game Whac-a-Mole by pressing down on an ever-shifting target button as rapidly as possible.
Subjects then listened to recordings of babies crying, adults crying or birds singing, and played the game again.
"We saw better scores and more effortful pressing after the infant cries," Dr Young said.
Candy Crush and a crybaby: sounds like the perfect pair.