Colonization has long been a way for some nations to gain wealth and influence. The African continent has experienced colonization for more than two millennia. The colonization of what was to become the Americas began in the early part of the 16th century, before which Indigenous Peoples had their own kinship and governance structures, ceremonies and belief systems, as well as knowledge developed over many generations regarding a balanced co-dependent relationship with the land. A degree of cooperation initially existed between Indigenous Peoples and the Europeans who arrived, including the sharing of skills and knowledge, as well as trade and military alliances. Thus, at the outset, relationships with Indigenous Peoples were greatly valued—until they were no longer needed and viewed as an encumbrance. As settler populations increased, their desire for land and wealth grew. The colonization of Indigenous Peoples over several centuries was achieved by guns and by old-world bioweapons that comprised the introduction of smallpox, tuberculosis, and influenza that killed more people than settler bullets did. In fact, in what is now Canada, the Indigenous population pre-colonization was estimated to have been between 350,000 and 500,000 (but some estimates have it as high as 2 million), but declined to just 125,000 by 1867.

In addition to the physical appropriation of land was the colonial effort to eliminate the transmission of cultural identity, traditional skills, and connection to the land. Beginning in 1883 (while this was the date of the first federally established church school, similar institutions existed as early as the 1830s, years before Canadian federation) Indian Residential Schools (IRSs) were established in Canada (as were American Indian Boarding Schools in 1862). Children were forcibly removed from their families and were institutionalized in IRSs with the explicit goal of ‘taking the Indian out of the child’. These mandated church-run IRSs endeavoured to save the souls of the ‘savages’ by immersing them in Euro–Christian beliefs and eradicating access to traditional socialization values, language, practices and ways of life. By the 1930s, roughly 75% of First Nations children attended IRSs, as did many Métis and Inuit children. The last of the IRSs was closed in 1996, but by then several generations of children had experienced the mistreatment that abounded in these institutions.

While the treatment of children varied across the different IRSs, they frequently experienced harsh and denigrating conditions [1]. In addition to physical, emotional and sexual abuse and neglect, children were stripped of their identities, made to feel ashamed of themselves and their culture, and denied the use of their language, beliefs, and ways of being. Some IRSs were associated with Indian hospitals where sick children were transferred but, owing to poor isolation procedures, diseases such as tuberculosis were often acquired. Indian hospitals were not intended to administer treatment that incorporated traditional medicines, midwives or holistic strategies; rather, the hospitals’ assimilationist goals were to replace traditional healing with Western biomedical procedures [9]. In the Indian hospitals, which treated Indigenous patients in addition to IRS students, non-consensual sterilization was commonly undertaken (such non-consensual operations were performed on Indigenous women even as recently as 2018). In some IRSs, nutritional experiments were conducted from 1942 to 1952 to determine whether vitamin supplements (riboflavin, thiamine, niacin, and bone meal) would limit the effects of purposefully introduced malnourishment. These experiments continued despite the deteriorating health and increased mortality of children, and the developmental delays that were produced [10]. Indeed, these experiments continued well after the UN Convention on genocide was signed. The consequences for IRS survivors resulted in marked and varied repercussions on health, which has been elucidated in detail in a tragically poignant report [11].

The trauma did not end for children once they were released from the IRSs. They were returned to reserves that had been subjugated into poverty, and where they felt disconnected from their families and communities. There was much discord between community members, often instigated by prior conflicts (bullying) brought about by a need to survive in the IRSs [12]. Moreover, on some reserves, divisions existed between members who had internalized the religious precepts imposed on them at the IRSs, whereas others were intent on maintaining traditional Indigenous ways of life. Thus, where communities had operated as cohesive collectives, the IRS experience fostered divisions and conflicts over fundamental values. Further contributing to dysfunction in some communities, adult survivors frequently experienced shame and guilt owing to their powerlessness in protecting their children or siblings from the IRS experience, resulting in coping behaviors that were self-abusive or abusive of others.

Although the experiences of the children who attended the IRSs and the consequences that emerged are relatively well known, far less attention has been directed toward the Sixties Scoop. During the period from the 1950s to the 1990s, about 20,000 Indigenous children in Canada were removed from their families and communities by child welfare services. Indigenous children whose parents attended IRSs were at greater risk of experiencing childhood adversity in their homes, thus increasing the likelihood of their removal and placement with non-Indigenous foster parents, adoptive parents, and in group homes, often permanently separated from their families and from their cultural identity [13,14].

Even today, despite representing only 7.7% of the Canadian population, Indigenous children represent over half (52.2%) of children aged 14 and younger in foster care, described as the ‘millennial scoop’ [15]. Remarkably, there are currently more Indigenous children in the care of the child welfare system (CWS) than there were in IRSs at any single point in time [1]. In numerous regional jurisdictions in Canada, there remains a policy of putting expecting mothers, disproportionately those who are Indigenous, on ‘birth alerts’, with social workers being present to apprehend a newborn infant immediately following the birth without parental consent. Even in regions where birth alerts are no longer official policy, it has been suggested that the practice continues, largely due to systemic biases within the CWS. There is growing evidence that the overrepresentation of Indigenous children at risk of apprehension by the CWS can be ascribed to social and economic inequities [13,16,17], most of which are linked to the continued legacy of governmental forced assimilation policies [13]. Sadly, experiencing the child welfare system is predictive of poorer mental health outcomes, along with juvenile and adult incarceration in the criminal justice system. In addition to affecting the children taken, these experiences promoted profound mental health consequences in parents [18].

Colonialist actions involving policies such as the IRSs and the Sixties Scoop, along with forced relocations and the restricted movement of Indigenous community members, have contributed to the erosion of the knowledge of the land that was passed down through generations. Treaties were created that were regarded by settlers to represent a surrender of the land by First Nations. The Indian Act restricted First Nations Peoples to reserves and diminished access to the broad resources of their ancestral territories either by limiting practices, physical access, or by developments that destroyed the land, contaminated the water, or eradicated traditional ways of life and livelihoods. As with so many Indigenous populations globally, the land is not perceived as an object to be possessed. Instead, the plants, animals, and waters are viewed as ‘life’ and inter-connected relationships, as ‘members of the larger other-than-human community’ [19]. Thus, the systematic removal of Indigenous Peoples from their lands and the development (desecration) of traditional territories, ranging from clear-cutting to changes to waterways (hydro dams) to fracking and pipelines, to the toxic disposal of pollutants in the air and water systems, all constitute traumatic insults with incumbent consequences [20]. The Canadian determination to establish sovereignty in remote areas (e.g., the Arctic circle) involved the duplicitous relocation of Inuit families to thousands of kilometres from their home territories. Elders have recounted decreased physical, mental, and emotional health after experiencing dispossession from the land [21]. Spiritual impact and loss are felt related to the inability to pass on traditional Indigenous knowledge to younger generations; reduced access to the land preventing its use for ceremonies, traditional practices and sustenance; the reduced ability for water to give and support life; the loss of language that is essential to express their connection with; and lost knowledge of the land [21,22].

Beyond colonial exploitation of the land, environmental racism and climate change are impacting the health and well-being of Indigenous Peoples, especially in the north [23,24]. The most recent report of the Intergovernmental Panel on Climate Change [25] points to climate change as a contemporary manifestation of colonialism. In this regard, colonialism is implicated as both a driver of climate change and in exacerbating the vulnerability of Indigenous communities. When the land is the main source of sustenance, the inability to predict environmental phenomena or the lack of tools to contend with such changes can have particularly devastating effects on well-being at both the individual and community level. Many Indigenous communities have been contending with critical environmental issues, including the toxicity of local bodies of water and exposure to natural and human-made disasters, such as floods and forest fires. When such events force displacement, temporarily or permanently, there is the additional diminishment of the safety and security of displaced populations. Under these conditions, resources (e.g., financial, along with basic needs such as water, food, and clean air) are stretched or no longer accessible, family and community members may be divided or lost, safety and security are undermined, and exposure to potential toxicants and disease are heightened. Warming temperatures, as well as changes in weather patterns and ice stability, have altered access to resources critical to community survival and created barriers to community members’ participation in land-based practices and ways of life, resulting in diminished cultural identity and well-being [23,26]. These effects are occurring even though Indigenous Peoples’ ways of life are least likely to be contributing to the human-made impact on the climate. On the contrary, many of the environmental disasters that have affected the lives and livelihoods of Indigenous Peoples in Canada have, at their roots, industrial developments by corporations with no or minimal Indigenous representation, consultation or benefit.

The built environment of Indigenous communities may further promote severe health issues. Government programs that control the building of homes and infrastructure in fly-in and northern communities apply standards that are not only inappropriate for the climate [27,28], but disregard the cultural and social needs associated with familial and community living. Homes were built with standard designs defined by government agencies (‘Indian Houses Type 1–7’), all with similar floor plans. This strategy undermines traditional family structures and diminishes individuals’ identification with their living spaces [27,28]. The houses in these communities are often built below acceptable quality standards, and without consideration of the high cost of transporting materials to remote communities, thereby limiting the number of new homes and extending the time needed to build.

A failure to include Indigenous perspectives in decision-making continues to severely limit progress for self-determination in housing [28]. The lack of reconciliation in housing policies combined with the substandard construction of homes on-reserve has resulted in statistics that have remained unchanged for decades; in 2006, 44% of on-reserve First Nations homes required major renovations and 36% reported living in overcrowded conditions, and these numbers were still evident in 2016 [29,30]. It has been noted that, ‘The consequence of this crisis is that the home, which for First Nations people has traditionally been a place of pride and identity, instead today exacerbates many social and health problems’ [27] (p. 2). Some of these social problems contribute to intergenerational trauma, including numbing the pain by substance misuse and other related negative coping mechanisms [31].

Colonization as it is recapitulated in current times meets the key criteria of Article II of the UN Convention on Genocide. The intergenerational effects of historic and ongoing systemic racism have had considerable implications for the health and well-being of Indigenous Peoples (Article IIb). Mental health problems are endemic among Indigenous populations; depressive disorders, anxiety, PTSD, and substance use disorders occur at inordinately high levels. In many First Nations and Inuit communities, the occurrence of suicide has been much higher than in the remainder of the Canadian population. The frequency of suicide varies across communities, ranging from 2 to 10 times that of non-Indigenous people, and it is especially disconcerting that over the last two decades suicide has occurred more frequently among young people. This is similarly apparent among American Indians and Alaskan Natives, in whom suicide occurs at 2.5 times the frequency of the population at large.

Understandably, a significant level of distrust between Indigenous Peoples and healthcare professionals exists. Given women’s experiences of forced sterilization, birth alerts, and the removal of children as a result of various policies over generations, the fear of child apprehension is so deeply rooted that some mothers may refuse skin-to-skin contact, breastfeeding, and other bonding strategies because they expect their child to be taken from them (Articles IId, IIe). This learned distrust of healthcare professionals jeopardizes the willingness of expectant mothers to disclose their medical, physical, mental or substance use history. Such mistrust is particularly evident among Indigenous women in fly-in and northern communities. The medical and healthcare services offered in such communities are often limited, forcing expectant mothers to leave the community to deliver in larger, urban, mainstream hospital facilities, and those who experience pregnancy complications are sometimes away from home for extended periods of time. Forced obstetric evacuation is particularly stressful, as due to the nature of medical funding that is applied to Indigenous Peoples, women are typically separated from family and community support for the final weeks of pregnancy, putting a notable strain on the health and wellness of both mother and child. This may contribute to the increased risk of medical intervention during labor, as well as postpartum depression, along with the negative developmental consequences of stress on the fetus, and may even account for why the mortality rate of Indigenous infants is 2–7 times higher than non-Indigenous infants [32]. The loss of the birthing experience and related ceremonies in communities is perceived as a cultural loss and forced evacuation has been long associated with colonial practices.

Just as colonialism continues to influence Indigenous entrance into the world, it also influences death. The built environment hinders the palliative care that reflects the values of Indigenous Peoples. A lack of healthcare access on reserves and inadequate housing that does not allow for proper care necessitates aging individuals leaving their community to access care in a hospital setting [29,33,34]. While the majority of Indigenous people would prefer to pass away at home, many die in urban hospitals where the physical structure of the hospital building or prohibitive administrative policies can prevent end-of-life care that aligns with Indigenous values. In addition, this stage of life is often a time of sharing stories and passing on knowledge, and so death in urban hospitals is another form of systemic racism that further marginalizes Indigenous ways of knowing [29].

2. Neurobiological Consequences of Early-Life Trauma

Intergenerational Consequences of Prenatal Stressors

3. Epigenetic Changes Related to Stressful Events

5.1. Epigenetic Changes Associated with Prenatal Stressor Events

5.2. Transgenerational Transmission through Epigenetic Changes