The Evolved Nest
There are several periods in life when brain development is most malleable: gestation, birth, the first five years after birth, early adolescence, emerging adulthood and therapy. But the most influential periods for human development (and those where the effects have been noted more closely) appear to be during gestation and the first five years of life. With 25% of the brain in place at birth, the first five years of life encompass the most critical time period for human neural development. They encompass the “genesis of the nervous system, the road-building time when neurons are born and axons navigate the chartless expanse of the embryonic brain to found synapses,” (Niehoff, 1999, p. 274). For optimal functioning later, the young brain “must be protected during development from factors that impair growth, damage neurons, or interfere with the formation of synaptic connections” (Niehoff, 1999, p. 274).
By the end of the first year, the brain reaches 60% of its adult size. Brain volume will be perhaps 75% complete by age 3, 90% by age 5. Volume isn’t everything though. Myelinization (glial cells facilitating communication among neurons) of several brain systems occurs in the first years of life (e.g., somatosensory, auditory) with the visual system completed by 4 months of age (Bronson, 1982). We can see from the early-developing visual system that there is a critical period for its optimal development. If a child has an uncorrected lazy eye or kittens are prevented from seeing during the sensitive period, there is no going back to redevelop the capability. Similarly across the brain the way things are connected or not, how many receptors there are, the thresholds for their activation, have sensitive periods for optimal development. All matter too for a well-functioning brain. These, along with volume, are influenced by early experience. So, although development per se proceeds in an evolved order, timing and sequence, how well it goes depends on external factors, primarily caregiving. And with each layer of development, the range of options narrows, as early developing systems form the foundations for later-developing systems.
Why does the evolved nest matter? Early years are when virtually all neurobiological systems are completing their development. As mentioned, there are sensitive periods throughout the first five years of life in which particular caregiving is expected by the maturational schedule of the child. When expected care is not forthcoming, development will be less than optimal. The Evolved Nest is the baseline for species normal care.
And it is a matter of justice for young children. The concern for young children and their caregivers is rooted in a concern for justice. To notreceive human nest in early life can be perceived as an injustice to a child, with serious ramifications for the child’s future.
RESTORING HUMAN NATURE
PRIMAL KNOW HOW FOR WISE LIVING
Every animal has a nest for its young that matches up with the maturational schedule of the offspring. Humans too! The Evolved Nest (or Evolved Developmental Niche, EDN, refers to the nest for young children that humans inherit from their ancestors. It's one of our adaptations, meaning that it helped our ancestors survive. Most characteristics of the evolved nest emerged with social mammals more than 30 million years ago.
The USA is experiencing a decline in child and adult physical and mental wellbeing, with for example, everyone under age (in 2018) 55 at a health disadvantage compared to other advanced nations (e.g., National Research Council, 2013).
The baselines for normal childrearing have shifted in the USA. Many people seem confused about what children need and what appropriate childrearing is. With little attention to our deep history, it is easy to believe anything. Parenting seems more about how little of children’s needs can be provided to children and still have them reach adulthood intact. At the same time, children’s health and wellbeing have deteriorated (OECD, 2009; UNICEF, 2007), young children’s aggression and psychotropic medication levels are on the rise (Gillam, 2005; Powell, Fixen & Dunlop, 2003), and anxiety and depression are at epidemic levels for all age groups (USDHHS, 1999).
With only 25% of the brain fully developed at birth, the first three years of life encompass the most critical time period for human neural development. As Niehoff (1999) describes, for optimal functioning later, the young brain “must be protected during development from factors that impair growth, damage neurons, or interfere with the formation of synaptic connections” (p. 274). During the first two years and the introduction of the child’s systems to the surrounding environment, the immune system “uses early experiences to elaborate a repertoire of antibodies that will determine future vulnerability to infectious disease” and sets the thresholds for stress response used for a lifetime (ibid, p. 274).
The stress response system must be protected from “either collapsing or overheating” due to challenges it is not yet prepared to handle (ibid, p. 275). It is apparent that US children are not being protected from early toxic stress and its subsequent effects on neural and immune functioning (Shonkoff et al., 2012).
Every animal has a nest for its young that forms part of an extra-genetic inheritance corresponding to the needs and maturational pace of offspring (Gottlieb, 1991; Oyama, Griffiths & Gray, 2001). Humans evolved to have the most helpless newborns and the most intensive caregiving niche. Childrearing practices consistent with the human nest were practiced for over 99% of human genus existence and still are in some indigenous cultures. Intensive caregiving in early life includes nearly constant touch, extensive breastfeeding, and free play with multi-aged peers as well as positive social support for the mother-child dyad and multiple adult caregivers (Hewlett & Lamb, 2005; Hrdy, 2009). All these caregiving practices are correlated with physical and mental health outcomes, but also with social and moral development.
Human development is biosocial: healthy bodies, brains and sociality are formed from family and community life experience in early life. If brain and body system thresholds are established suboptimally in early years—not by trauma, but simply by not providing care that children evolved to need, then children may not reach their potential. They may show underdevelopment of concern for others, a sense of social responsibility, and global citizenship.
IMPORTANCE OF THE NEST
Human Immaturity at Birth
Human babies are born early. For several months postnatally relative to other primates, human babies share characteristics of fetusesrather than infants of other primates (Trevathan, 2011). For example, in terms of bone growth, a human baby’s ossification of phalanges is similar to that of a gestational macaque and does not reach macque neonate levels for several years. Apes have developed cranial plates whereas the human neonate’s are mobile to facilitate birth and do not settle for several months afterwards (Schultz, 1949). Among primates generally, the brain of a newborn is half the size of an adult’s brain. Using primates as a model, humans should be born at 18 months of age (Trevathan, 2011). Although all apes are born earlier than the typical primate, humans are the most immature, with only 25% of the brain developed at full term birth. See Table 1.
We have not evolved away from being mammals. Ancestral parenting practices provide the best baseline for understanding how to provide what children need. Following evolved nest practices, will foster better mental and physical health for the long term.