The significance of an evolutionary approach to public health is increasingly being recognised. The negative effects of poverty and inequality are also being recognised as a huge burden on health. Occasionally, the two are even combined to acknowledge our evolved responses to inequality.
Overall though the various efforts seem to have stopped short of explicitly proposing an evolutionary explanation to the Spirit Level evidence between countries. Understandably, the focus has been on measures like teenage pregnancy and breastfeeding rates that directly measure life history (LH) strategy (see this post on LH theory). But other outcomes may be the result of a faster LH strategy too: infant mortality may be higher in more unequal countries because of a reduced biological investment in each child, leading to low birthweight and prematurity.
The other outcomes in the Spirit Level can be brought under the life history strategy umbrella too, with its general principle of short-termism. The harsher and more unequal the social environment, the more uncertainty there is over long-term prospects. This would have been true in our ancestral environment too, and with morbidity and mortality rates so much higher, the selection pressure on behavioural strategies would have been extremely strong. The danger of dying before or during reproductive years made early reproduction paramount. As a result, we evolved a comprehensive response to harshness, which speeds up the course and development of key life stages, and prioritises reproduction over growth.
The response is evident in various domains:
Biologically, periods of growth are shortened, and puberty is brought forward. As in Barker’s thrifty phenotype hypothesis, where less important organs like the pancreas get less energetic investment when energy is scarce, physical size is sacrificed to allow reproduction to occur earlier. This under-investment early on in life may lead to the various health problems that develop later. Of course middle-aged health problems wouldn’t have been a major problem evolutionarily, if the early reproduction meant that your genes had been passed on in a difficult environment. They may not even have developed, with an environment of low calorie availability and an active lifestyle avoiding the metabolic disorders seen today. The molecular symptom of quicker development is oxidative stress, which is a measure of the biological stress on an individual. It is linked with chronic low-level inflammation and suppression of the immune system. Heightened cortisol levels, and activation of the hypothalamic-pituitary-adrenal axis which releases adrenaline, are also implicated. The response to stress is complex, but the various measures are consistently related to low socioeconomic status, and so can be argued to be part of the fast LH strategy.
Cognitively, people show a higher rate of a cognitive bias known as future discounting. This involves taking smaller, short-term gains at the expense of larger, long-term ones. Delaying gratification and impulse control require a low rate of future discounting.
Behaviourally, this bias could be argued to underlie almost any of the behavioural problems in the Spirit Level – drop-out rates from high school and low educational attainment, unsustainable environmental practices, addiction of any kind, from gambling to alcohol and drugs. Public goods problems (like climate change) require a long-term assessment of costs and benefits, so a bias to discount the future is disastrous for agreements on action. Hierarchy also encourages conspicuous consumption to signal status – another unsustainable practice. Future discounting may explain why trust is lower in more unequal countries, as a long-term view is needed to help someone today, when you may not be paid back for a while.
Parental investment is another feature which is sacrificed in the fast LH strategy. This is seen in harsher parenting styles. Parental inconsistency has been linked with elevated levels of stress hormones in children. And one of the parents may not even be there – 26% of families in 2011 were single-parent households. Absent fathers account for the vast majority of these. The effect on boys is the development of excessively masculine traits; girls hit puberty earlier. Both genders are more likely than average to repeat their parent’s lifestyle. The UNICEF index of child wellbeing correlates negatively with inequality, as do childhood behavioural problems.
Consequently, mental health suffers in unequal societies – especially anxiety. This can’t be said to be adaptive in modern society, but as with chronic stress, it is possible to theorise how it could have helped in an ancestral environment. In small doses, anxiety and low mood may have been one way of avoiding conflict, by avoiding aggression from others. But as with stress, constant exposure is pathological.
Inequality, by stratifying the social hierarchy, favours competition over cooperation as the way we interact with each other. Status becomes more important, as it has always signalled an ability to access resources, including mates. Excessive inequality means that those at the top can monopolise resources, and those at the bottom have nothing to lose when they try to climb the ladder. This manifests itself in higher rates of violence and homicide. Men may go to greater lengths to keep partners as well as compete for them, using violence and sexual coercion. The violence statistics don’t include sexual violence due to international differences in definitions, but (not unrelatedly) the status of women and gender equality are better in more equal countries.
In order to bring about the policy changes necessary to reduce inequality, disparate interest groups need to be made aware of the wide-ranging effects of inequality and the associated LH traits, in order to campaign with a louder voice together. This means physical and mental health organisations, alcohol and drugs charities, violence reduction schemes and so on could benefit from coming together to work for something that would tackle all of their respective issues at source. It’s not about creating a ‘natural’ environment – there’s no such thing, as we adapt to vastly different societies. It’s recognising that a more equal society brings out the best of our nature.