A little over 200 years ago, Thomas Malthus, a Cambridge academic and Anglican priest, wrote a highly influential text that made Malthus an "ism" in his own life time. Its key ideas still resonate strongly today.
The central argument of Malthusianism proposes that population growth - if left unchecked - will always outstrip natural resources, leading inevitably to poverty, pestilence and famine. For Malthus this was just Mother Nature being cruel to be kind, tough-love at the population level.
Since Malthus's time, technological advances in areas such as agriculture and health have enabled us to attain and sustain ever larger and denser human populations. And rather than famine many nations presently suffer the opposite problem, namely overnutrition.
There are of course downsides to our increasingly dense populations; one issue I'm particularly interested in is the apparent link between dense populations and mental illness.
There's been a lot of research looking at this relationship between population density (number of people per square kilometre) and mental health. Possibly the most convincing study to date was published in the British Journal of Psychiatry in 2004.
This particular study followed the entire Swedish population (4.4 million people aged 25 to 64) over a four-year period. The study found that in localities where population density increased, so too did the incidence rates for psychosis and depression. Those living in the most densely populated areas had a 68 per cent greater risk of developing psychosis - and a 20 per cent greater risk of major depression - than those living in the least densely populated areas.
Closer to home, a study undertaken by researchers at United Arab Emirates University (UAEU), published in the International Journal of Geriatric Psychiatry, set out to obtain baseline data on the mental health of the UAE's elderly population.
This study used a random sample of 843 households across Al Ain, Ras Al Khaimah and Dubai. Overall the finding suggested rates of depression and anxiety comparable with other international studies which, by itself, is pretty unremarkable.
What is interesting however, is that when the researchers looked more closely at the data they found that the prevalence of depression for Dubai was 29 per cent, which was significantly higher than that for Al Ain (11 per cent) and RAK (12 per cent).
As in the Swedish study, the researchers took into consideration important demographic variables. But even after controlling for these the Dubai residents still showed significantly higher rates of depression. Population density is one possible explanation for this finding; Dubai is far more urbanised than either RAK or Al Ain.
As part of our own emotion-focused research programme at Zayed University, called Arabia Felix, we decided to undertake a small study to further explore the population density hypothesis here in the UAE. Dr Mouza Mohammed Al Yahed and I set out to study depressive symptoms amongst two distinct communities in RAK.
One group were urban city-centre dwellers, the other group resided in the less populated Al Humrania district. All participants were adult Emiratis attending primary healthcare clinics, and both groups were roughly matched for age, gender and marital status. And as we predicted, rural dwelling Al Humrania residents had significantly lower levels of depressive symptoms than their urban compatriots.
Why is this? One possible explanation concerns the levels of stress and social support people experience in population-dense urban environments. Compared to rural residents, research suggests people in cities experience more stress and less social support. Paradoxically, our biggest, most population-dense cities can be the loneliest places on the planet.
Perhaps future advances in technology will address the psychological aspects of our mass living arrangements. By 2030 the Earth's population is expected to reach 8 billion, the same year depression is projected to become the world's second leading burden of illness, and No. 1 for women. Our technological triumphs have undoubtedly helped us sustain huge populations, but so far they have contributed very little to our psychological well-being.
Justin Thomas is an assistant professor of psychology at Zayed University