The biology of babies

Why does my baby need so much care?

Babies are born very immature and take a long time to develop and reach adulthood. That’s why they need so much attention. After nine months inside their mother in a quiet, dark, and warm space, they suddenly need to breathe, and to deal with noise, light, and cold. They feel hunger and pain for the first time. They can’t walk, feed themselves, or stay warm, so they are completely dependent on their caregivers for survival. Babies understand the world based on how it makes them feel. If they feel safe, fed, and warm, their needs are met and they can develop to meet their highest potential. If they feel unsupported, in pain, sick, or mishandled, their stress response is activated. It can become toxic and cause lifelong harm. Breastfeeding increases a mother’s ability to respond to her baby’s needs and helps the attachment of the baby to the mother.

A) Why babies need a lot of care

Babies have to navigate the abrupt transition to live outside of the uterus and are then unable to survive without extensive support from their caregivers because of their immaturity. Indeed, babies are born so immature that the first three months after birth is sometimes called the fourth trimester (Zeveloff 1982). 

As a result of their immaturity, newborn human babies cannot:

  • Stay warm. 
  • Hold their heads up.
  • Hold onto their mothers.
  • Walk.
  • Feed themselves.
  • Stay warm.
  • Protect themselves.

The young of other mammals start eating, reach adult size, and reproduce at a much earlier age. A baby deer can start following its mother at one week of age; humans can’t walk until about one year after birth. 

Humans take a long time to grow up and function independently. This means that babies need a lot of protection and support from their caregivers over many years. 

B) Babies are very immature

There are a number of possible reasons for babies being born immature and taking a long time to grow up.

1) Pregnancy is limited to 40 weeks

There are many ideas about why human pregnancy does not last longer than 40 weeks, giving the baby more time to develop. Two popular ones include:

  • The narrowing of the pelvis, which allows humans to walk upright, prevents the birth of an older baby with a bigger head.
  • The energy demands of a rapidly developing baby on the mother’s body limit the length of the pregnancy (Dunsworth 2012).

2) Our large and complex brains 

Our large and complex brain quadruples in weight between birth and four years of age when it reaches 90% of its adult size and is only fully mature in the mid-twenties (Dekaban 1978). The brain of the baby is relatively underdeveloped and babies need extensive support from caregivers to survive, learn, and thrive.

3) The complexities of human life

Babies have a lot to learn: language, social structure, the patterns and practices of the group. This type of knowledge cannot be coded into instinct inside the uterus; it must be acquired after birth.  

C) The big transition to life outside of the uterus

Babies face huge changes as they are born. For nine months, they have been in constant contact with their mothers while floating in a dark, soft, quiet, warm, snug ball and receiving constant nutrition.

At birth, they have to breathe, the lungs have to inflate, and the heart needs to send more blood to the lungs. At the same time, babies are often bombarded by light, sharp objects, noise, cold air, and even pain. They are no longer held snugly and may be separated from their mother. They also feel hunger and have to feed themselves. In short, the environment they have known for nine months is gone and replaced with a much more challenging one.

D) Attachment to the mother (bonding)

The mother's body provides emotional security for the baby. Photo by Dakota Corbin on Unsplash

Babies understand the world based on how it makes them feel. They respond to those feelings. If they feel safe, fed, and warm, they relax and continue to develop and meet their highest potential.

Mothers and other caregivers are the buffer between the baby and the world. When mothers hold their babies and respond to their other needs, mothers recreate some of the characteristics of the uterus. This familiar environment protects and calms the babies and allows them to thrive in the first months and years after birth as their bodies and brains develop (McKenna 1994; Winberg 2005).

Caregivers are also a base for the babies to return to when they are sick or afraid (Gibbs 2018). This is known as attachment or bonding. Secure attachment usually leads to good social and emotional development and less anxiety (Fearon 2017). A lack of secure attachment has long-term negative health effects (Puig 2013). These effects may be mediated by changes in the baby’s genes (Craig 2021).  

E) Maternal responsiveness

Maternal responsiveness is when a mother tends to the baby’s needs by listening to their babies, holding, and caring for them. It allows babies to have safe experiences as they learn, grow, and become more independent

If they feel unsupported, in pain, sick, or mishandled, their stress response is activated and this may have long-term consequences.

Maternal responsiveness is essential for babies to build secure attachments.  Studies have shown that:

  • Babies are more relaxed when with their caregivers and separation is stressful for them (Curtindale 2018; Reynolds 2018).
  • Babies are more relaxed when their caregivers are affectionate and respond to their needs (Berlin 2019; Waynforth 2007).
  • Babies of attentive mothers have fewer chemical indicators of stress in their blood (Bugental 2003; Champagne 2001).
  • Mothers who respond to their premature babies improve their babies’ language and motor development, attachment, security, social and emotional development, and future health (White-Traut 2018).
  • Children whose needs are met before they become upset are more likely to be independent and are less distressed by pain and fatigue (Abraham 2018; Stein 1994). 
  • Toddlers who talk and interact more with their parents show significant increases in thinking and language function (Gilkerson 2018).

As babies grow and develop, they become more independent and able to tolerate separation but the exact timing is very individual.

F) How breastfeeding encourages baby attachment and maternal responsiveness

Studies have shown that breastfeeding mothers are more responsive to their babies and that the longer the period of breastfeeding, the more responsive the mother becomes (Linde 2019; Peñacoba 2019; Whitfield 2019). One study found this effect persisted in mothers of children as old as 11 years (Weaver et al. 2018).  As one example of responsiveness, effective breastfeeding requires that mothers learn, understand, and respond to their babies’ hunger signs (Smith 2001).

Breastfeeding promotes secure attachment as it offers babies a warm, familiar place in which to obtain milk which is always ready and at the same temperature. 

The level of cortisol, a hormone related to stress, changes during the day and night. Cortisol levels in breastfed babies parallel the mother’s during the first year. This connection is less consistent in babies who are fed infant formula (Jonas et al. 2018). This is a good example of the tight connection that breastfeeding creates between mother and baby.


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