Hilary Boden explains how age affects us all

A study recently published by the Archives of Sexual Behaviour suggests that major life decisions are subconsciously influenced by how long people believe they will live. The theory of “life history evolution” predicts life expectancy to influence major life decisions in humans, as it does in the lives of other animals. The developmental timing of sexual maturity, relative to species-speci?c lifespan varies widely. Some animals mature quickly and produce offspring at very early ages, while others take much longer to fully mature and therefore reproduce only after several years. This variation is due to natural selection intending to maximise the fitness of offspring and increase the chance of future survival. “Life History” theory suggests that people may alter the timing of life events such as marriage and reproduction in response to the prevailing level of life expectancy in their local environment.

The study, carried out by Dr. Daniel Krupp, a post doctoral fellow at Queen’s University, analysed population data from Canadian jurisdictions, which included information about people’s age and their marital, reproductive, and educational behaviours. According to “life history evolution” hypotheses, indicators of reduced life-span should lead to younger marriages and earlier births, whist longer life spans would see a greater chance of divorce and lead to a greater investment in education. Thus, Krupp carried out the study as a means to test the validity of such theories, and to answer questions which have challenged psychologists interested in human family structures: Why are certain individuals more likely to marry and have children early? And why are some others more likely to terminate their marriages or pregnancies?

The statistical results confirmed at a regional level that an increase in life expectancy at birth was associated with an increase in the ages of reproduction and ?rst marriage, as well as increases in the rates of abortion, divorce, and measures of educational attainment. This pattern was highly consistent, with 18 out of 19 tests being in line with the “life history” hypothesis. Other studies also reveal a similar relationship between life expectancy and life choices: Bulled and Sosis (2010) observed in a comparison across nation-states that life expectancy was positively associated with educational investment and negatively with adolescent birth rates. Similarly, a study by Nettle (2011) carried out across English neighbourhoods saw that the age at which women had their first child increased with female life expectancy. Dr. Krupp says that these results “suggest that perceptions of life expectancy are important to human decision-making processes. Accordingly, future research should attempt to describe the psychological mechanisms involved in the perception of and response to life expectancy cues.”  Krupp goes onto suggest that such cues may include how individuals asses their own health, the predictability of resource availability in their environment, or the survival and longevity of their relatives and neighbours. Traumatic or chronically threatening events, as well as stressful environments are posited to likely affect a person’s perception of life expectancy.

However, a conscious evaluation of life expectancy may not be necessary for it to affect reproductive decision making. Many species which are not likely to have consciousness, such as wasps and scorpion-flies, are capable of altering their reproductive behaviour in response to cues of foreshortened time horizons. Thus, conscious input may not be required. Our environments and subliminally perceived longevity may be having a huge impact on our life decisions without us even realising.


Hilary Boden


Image by ell brown