Evolutionary biology basics + busting evolutionary biology myths for health professionals who work with parents and infants

The Possums programs are foundationally embedded in the most up-to-date understandings of evolutionary biology

Evolutionary biology foundationally informs the Possums programs (or Neuroprotective Developmental Care). We learn from evolutionary biology that in a time-developmental universe, systems diversify - complexify - over time. Therefore, complexity science also foundationally informs the Possums programs, since we are focussed on how to support the flourishing of certain biological systems (in our case, of the mother and baby, the family, health systems who care for them etc).

Whilst the analyses below address key myths, the principles of evolutionary biology are intimately woven into the Possums programs in much greater detail than can be shown in high level tables on this and related pages.

Homo sapiens is a biocultural species - a living site of biological and cultural entanglement

A key evolutionary biology concept is that Home sapiens is, uniquely amongst all life forms, a biocultural species.

• Our heredity is determined by DNA coding, which holds instructions for building and operating life passed down from Deep Time in an extraordinary process of natural selection from the last universal common ancestor (a single celled organism) 3.8 billion years ago.

• Our heredity as Homo sapiens is also uniquely determined by cultural coding, which holds instructions for nurturing and operating human life, initially in oral traditions and stories, then also in writing - science, humanities, the arts - and these days increasingly mediated through, and explosively expanding in, our extraordinary digital realm.

  • Over the past 300,000 years, humans have complexified exponentially due to the way we have used tools to break free from the constraints of natural selection.

  • We've complexified and spread to inhabit all of the planet's biomes without altering our bodies anatomically, because of our staggeringly brilliant capacity to invent tools and technologies, which are passed down through cultural coding.

New humans, too, in evolutionary terms, are an entanglement of the biological and sociocultural. The cultural needs to support (not obstruct) the biological, for human flourishing.

A mismatch between biology and culture can impact negatively on the flourishing of biological systems

Each of these two forms of coding, genetic and cultural, are fundamental to the nature of our humanness. As health professionals who work with mothers and babies, we are adept at understanding and working with both. Each of us, in our professional role, forms part of a woman and her baby's experience of cultural heredity, as we act to support the flourishing of their biological processes.

• If health systems promote a culture-biology mismatch, our interventions risk interfering with the flourishing of human development.

• Because of the resilience of complex systems, most mother-baby pairs are resilient and flourish anyway despite cultural (health system) interventions which misalign with biological processes. But a small subset of susceptible infants and their families may suffer long-term adverse consequences. These are the families who urgently need our protection, through support in which biology and culture align.

This is why what you do every working day matters - now, and for future generations!

Infant care and evolutionary biology: busting key myths

#	Myth	Updated evolutionary science
1	The "Obstetrical Dilemma" hypothesis proposes that Homo sapiens infant born most neurologically immature of all primates because of large head size and narrow bipedal pelvis.	Midwifery practice is widespread culturally and likely to be a necessary part of Homo sapiens' biocultural evolution, optimising birth outcomes in the human context where foetopelvic fit is closer than in all other primates. (This close foetopelvic fit is not pathological, but evolutionarily stable for the human in the context of midwifery support.) Grunstra et al 2023 propose it's more likely that relative neurological immaturity at birth is explained by a complexity of factors, including developmental plasticity in response to environmental factors, the metabolic demands of our large brain, and natural selection pressures upon foetopelvic fit. Gunstra et al note that evolutionary compromises in complex organisms are the rule rather than the exception (and not confined to female human bodies). An "evolutionary entanglement of biological and sociocultural factors" underlie considerations of human childbirth and risk minimisation. I propose that the same applies to lactation support, and the support of families with babies, too.
2	The "Energetics of Gestation and Growth" (EGG) hypothesis proposes that birth is initiated when fetal energy requirements exceed the mother's maximum sustained metabolic rate, around 2.1 × basal metabolic rate of the non-pregnant, non-lactating condition.	See above.
3	The infant is an exterogestate foetus for the first three months of life, giving rise to the concept of the fourth trimester.	Postnatal brain development occurs at a foetal-like for the first year or so. The exterogestation period can be thought of as nine months postbirth, up until locomotion.
4	Mothers know how to best respond to, care for, and breastfeed their infants if they tune in to their 'natural instincts' or 'intuition'.	This concept does not align with evolutionary biology, which demonstrates the fundamental and unique role of cultural heredity in the evolutionary development of Homo sapiens. Caring for an infant draws on cultural repositories of knowledge developed up over many generations, and available to contemporary mothers from family, friends, health professionals, and a wide range of other sources. It is, however, important that cultural knowledge imparted to contemporary women, and environmental factors, don't disrupt her capacity to experiment with responding to her baby (a common contemporary problem). The idea of the 'natural' is often quite unkind of mothers, who then feel 'unnatural' when they strike infant care challenges. For this reason, the idea of the natural is not used in the Possums programs.
5	Too much left brain input interrupts the natural flow of a mother's right brain as she cares for her baby.	This simplistic framing of the left and right brain is based on popular conceptions from last century. Psychiatrist and researcher Dr Iain McGilchrist has demonstrated that the left and right brain necessarily work together, though life goes best for the human when the highly verbal, categorising left brain serves the right brain, with its physically aware, integrating, scanning and feeling-sensing skills. Possums argues that contemporary women need excellent evidence-based information which is assimilated by the left brain but which strengthens the right brain's capacity to sense, respond, and enjoy through experimentation with various physical or somatic infant care practices.
6	"We're not Kung! Peoples. Unregulated breastfeeds and sleep are incompatible with the demands of paid work and contemporary Western lifestyle."	I've heard this said in various contexts over the years, demonstrating an outdated, 20th century understanding of anthropology and evolutionary biology. Researchers had demonstrated high frequencies of night waking and breastfeeding in the Kung! People communities - shown in other research as not necessarily typical of other First Nations cultures. However, in traditional contexts, in addition to infant care day and night, women often played demanding roles in service of community and family, occupations which required high levels of attentiveness, alertness, and intellectual acuity if she was to protect loved ones and other community members from injury and danger.
7	Parents need to regulate the biology of infant feeds and sleep using clock-based methods and graduated extinction methods, in order to make life as manageable as possible now, and to create good habits which will optimise the child's future development, independence, and wellbeing from the 1950s, and has been a part of last century's scientification of parenting (often referred to as Scientific Motherhood).	This is not an evolutionarily aligned belief. It has been the standard Western approach for asserting control over the stress and distress that arise from feeding, sleep and cry-fuss problems (in the absence of effective clinical interventions). From an evolutionary perspective, biobehavioural synchrony across these domains between mother and baby, parent and infant, optimises mental health and wellbeing for parents, and optimises developmental outcomes.

Infant biological expectation is shaped in Homo sapiens' environment of evolutionary adaptedness

Human infant evolved in environment of evolutionary adaptedness as an exterogestate foetus for first 9 months of life. As a result, the human infant's developmental outcomes are likely to be optimised in the context of

1. Rich environmental stimulation, including

   • Prolonged physical contact with older children and adults

     • Diverse and constant social sensory-motor enrichment

     • High levels of postural variability

   • Multi-centric social interactions

   • Complex non-social environmental stimulation e.g. outdoors

2. Affect-driven, increasingly long, sensory-motor reciprocity chains with caring older children and adults

3. Breastfeeding, which optimises gut microbiome and metabolic, endocrine, and immune protection.

NDC hypothesis: biology-culture mismatch might alter developmental trajectories in genetically susceptible infants

This theory is developed in a research paper published in 2019. I used the lens of Autism Spectrum Disorder to explore the underlying research literature and build up the case that the Possums programs (or Neuroprotective Developmental Care) are the most developmentally protective, evidence-based suite of programs available today for families facing infant care challenges.

Recommended resources

Why an understanding of evolutionary biology is important for health professionals who work with parents and infants + busting evolutionary biology myths

A timeline of relevant evolutionary events for health professionals who care for parents and babies

Theoretical models currently used to explain infant crying in the first months of life

Busting myths about evolutionary biology and breastfeeding

Busting myths about evolutionary biology and infant sleep, cry-fuss problems, and sensory motor development

Selected references

Cordey C, Webb NM, Haeusler M. Take it to the limit: the limitations of energetic explanations for birth timing in humans. Evolution, Medicine, and Public Health. 2023;11(1):415-428. doi: 410.1093/emph/eoad1035.

Douglas PS. Appendix 2: Neurodevelopmental challenges and the crying baby. The discontented little baby book: all you need to know about feeds, sleep and crying. St Lucia, Queensland: UQP; 2014.

Douglas PS. Pre-emptive intervention for Autism Spectrum Disorder: theoretical foundations and clinical translation. Frontiers in Integrative Neuroscience. 2019;13(66):doi.org/10.3389/fnint.2019.00066.

Dunsworth HM. There is no 'obstetrical dilemma': towards a braver medicine with fewer childbirth interventions. Perspectives in Biology and Medicine. 2018;61(2):249-263.

Dunsworth HM, Warrener AG, Deacon T, Ellison PT, Pontzer H. Metabolic hypothesis for human altriciality. Proceedings of the National Academy of Science in the USA 2011;109:15212–15216, doi: 15210.11073/pnas.1205282109.

Falk D. Evolution of brain and culture: the neurological and cognitive journey from Australopithecus to Albert Einstein. Journal of Anthropological Sciences. 2016;94:99-111.

Grunstra NDS, Betti L, Fischer B. There is an obstetrical dilemma: misconceptions about the evolution of human childbirth and pelvic form. American Journal of Biological Anthropology. 2023;181:535-544.

McGilchrist, I. The Master and His Emissary: The Divided Brain and the Making of the Western World (New expanded edition) 2019. Yale University Press.

Brian Swimme and Monica DeRaspe Bolles. The Noosophere: the thinking layer of Earth. 2024