I’ve been a newborn baby doctor for the last 40 years. After about two of them I lost count of the number of babies I was seeing with so-called ‘colic’. So many endless nights, so many tears, so much screaming … and that was just the parents.

Because of these tired, stressed families, I developed a lifelong obsession to talk to them about this disorder. This information is laid out in the evolutionary biology and medical literature, and it’s also known by a large number of parents whose babies have been through it and who have learned by experience how to prevent it.

But the start of any discussion about the behaviour of babies must be made in the light of their evolution.

Humans, after they started to walk in an upright posture, developed an athletic pelvis with a narrow birth canal as a consequence. Later humankind also developed a big brain. In order to give birth successfully through this narrow pelvis, their big-brained babies had to be delivered when still small, way earlier in pregnancy than before. We had to birth our babies prematurely.

Biologists call our babies “exterio-gestate foetuses”. That is, they are foetuses on the outside. I’m sure you have heard of the ‘fourth trimester’ of pregnancy. Three in womb, and another in your arms.

This tells us what babies expect of us. They are the most immature of all placental mammals. They are so helpless they cannot even cling and hold on to their mother efficiently. They need to be held and protected; they need security and love, they need feeding frequently and on demand. We produce for them a dilute easily digested milk, designed for frequent feeding. We are a continuous contact species and have not evolved to be separated from our parents’ bodies for very long.

You can see how this might impact on babies’ crying behaviour.

But first, you need to make sure that the baby is not crying because they are hungry. Remember this ‘continuous contact’ milk is designed for frequent, even hourly, feeding. Their stomach can empty in 30 minutes. So if they are upset, try feeding them again.

Second, studies were done where large groups of parents were given diaries to record how much unsettledness, fussing and crying their babies had. The results were remarkable and consistent. Most babies start to become more unsettled at about 2-3 weeks of age, they are at their noisiest at 6 weeks, and then there is a gradual improvement until 3 months, when crying levels drop rapidly. Most of the crying was in the evening.

How much the baby cried and fussed depended on two factors.

How closely the baby was held and where s(he)spent the day. Babies close to their parents cried less (and fed more), and those separated in cots and prams, cried more.

The temperament of the baby – either settled and calm, or sensitive and ‘wired’.

The average amount of crying/fussing (at which half of the population cry more, and half cry less) in a Western society is 3 hours a day at 6 weeks. The babies in the developing world (or with attachment parenting) crying less and Western routine-based babies, separated in prams or cots, crying more.

These are all normal babies and the curve that describes this population of babies is a bell-shaped or ‘normal’ curve. This means that there are 10% of babies that are crying a great deal more than 3 hours, sometimes 8 hours or more, a day.

The studies about ‘colic’ say that the condition occurs in about 10% of babies. But it has exactly the same pattern as ‘normal crying’ as above. So what causes it? The vast majority of these babies have no pathology, no illness.

What this means is that these babies are merely on the highest centile for ‘normal crying’. They are still completely normal babies but they are more sensitive than average. No wonder after decades of research, no one can find a unifying pathological diagnosis. There isn’t one.