The Evolution of Humans: Why we co-sleep

The Evolution of Humans: Why we co-sleep

Since the dawn of time, humans, like all other primates have co-slept. Co-sleeping provided warmth at night, parental proximity allowed for alertness to danger to their child such as predators or enemies. It allowed mothers to breastfeed on demand even while they were asleep providing reassurance and nutrition to their child, and allowed fathers to play an active nurturing role, being close to their child at night. 

Survival of the fittest

Humans have evolved to breastfeed and bed-share, as can be seen through studies of tribal societies and still the most common way to sleep in Japan, Korea,India and most African countries. It has been proven that bedsharing reduces the risk of SIDS by half and facilitates increased breastfeeding rates. 

McKenna and Gettler say “safe bed-sharing may actually exert a protective effect against SIDS." Mothers sleeping next to their babies, they argue, and breastfeeding, is “an evolved suite of behaviors tracing humans' phylogentic roots as both primates and mammals."

What exactly does this mean? We as humans, are biologically driven to sleep like our primate ancestors who carry their babies in their arms all day and sleep with them by their side. Dr Sears states that countries with high co-sleeping rates have the lowest rates of SIDs e.g. Japan. Could this be because nature intended it to be this way? He says “infants who sleep near to parents have more stable temperatures, regular heart rhythms, and fewer long pauses in breathing compared to babies who sleep alone. This means baby sleeps physiologically safer.”

Humans are mammals. All other mammals sleep with their babies to keep them warm, feed them whenever they want, and protect the most vulnerable members of their pack/herd etc from predators or the weather. Humans are also primates. All primates share a sleep surface with an infant at least until they are weaned to facilitate breastfeeding and protect them from harm. 

If bed-sharing was bad and caused deaths, surely this biological drive to bed-share would have resulted in the extinction of our species, or at least the cohort who practiced this unsafe practice. 

Are we wired to bedshare? 

In an article in neuroanthropology, J. McKenna and Edmund P Joyce from the University of Notre Dame describe their physiological research and studies of sleep practices around the world. They state “Like human taste buds which reward us for eating what’s overwhelmingly critical for survival i.e. fats and sugars, a consideration of human infant and parental biology and psychology reveal the existence of powerful physiological and social factors that promote maternal motivations to co-sleep and explain parental needs to touch and sleep close to baby.”

Additionally, babies often need to feed at night because their tummies are so small and breastmilk has low calories, perfect for an infants tiny gut. Most mothers find that it is much much easier to breastfeed at night with their baby lying beside them than getting out of bed, and sitting a chair to breastfeed. 

Are our babies wired to bedshare?

Again, McKenna and Joyce state that our babies just want to be close to their mothers “irrepressible (ancient) neurologically-based infant responses to maternal smells, movements and touch altogether reduce infant crying while positively regulating infant breathing, body temperature, absorption of calories, stress hormone levels, immune status, and oxygenation".

In short - babies are much happier being close to their mothers. Compared to all other primates, human babies have the most underdeveloped brain when they are born (25%). Jordan Peterson mentions in 12 Rules for life that we have evolved so that babies can be born with optimal development but still allowing a mother to walk and run. If a baby stayed in its mother’s tummy until it was as developed as other mammal babies (for another year), a mother’s hips would have to widen so far that she would not be able to walk. So we have evolved to find a happy medium which is 9 months in the womb. After this, human mothers are almost like Kangaroos. The baby’s rapid neurological development over the next 12 months outside the womb is best suited to be as close to their mother as possible, with physical contact. This is the environment that they are adapted to. 

Cover Image by Gerd Maiss from Pixabay

Research 

https://www.ncbi.nlm.nih.gov/pubmed/17112752

http://evolutionaryparenting.com/tag/bedsharing/ 

https://neuroanthropology.net/2008/12/21/cosleeping-and-biological-imperatives-why-human-babies-do-not-and-should-not-sleep-alone/ 

https://www.mother.ly/news/the-scientific-case-for-co-sleeping 

https://www.eva.mpg.de/documents/Wiley-Blackwell/Fruth_Sleep_AmJPhysAnthr_2018_2627710.pdf 

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