A healthy environment is beneficial for us because of things like improved air quality, which reduces respiratory disease. Noise and air pollution also have demonstrated links with diseases like Alzheimer's. Climate change has a whole range of physical impacts on people, from heat stress to extreme weather events. There's even recent research which suggests that microbes in plants and fungi are beneficial to our health because they can help boost our immune system.

But the lesser-known impacts are the ones on our mental health and wellbeing. For example, levels of cortisol – a hormone linked with stress – decrease when people spend time outdoors. 

 

It's interesting that, from an evolutionary perspective, humans have spent 99 per cent of their history in nature as hunter-gatherers. Basically, it's the last 10,000 years out of a million (give or take) that we've been living in structured, urbanised environments.

There are two researchers, Orians and Heerwargen, who published a study in 1992 called 'Evolved responses to landscapes'. They outline the 'savanna hypothesis', which describes the wonderful idea that the innate need for a relationship with nature is driven by the evolutionary ‘ghost’ of the environment we evolved from in our brains. 

 

In other words, from an evolutionary perspective, we spent so long in the African savanna that it's part of who we are. We need those natural environments to give us a sense of mental calm. We aren't fully equipped to manage the levels of overstimulation we subject ourselves to in the modern city environment. 

Interestingly, this is not unlike another theory pioneered by two environmental psychologists – Rachel and Stephen Kaplan – in the 1980s. 'Attention restoration theory' argues that natural environments – pure, unthreatening landscapes – are something we can pay 'indirect attention' to. This form of attention, in turn, has a soothing effect on the brain. 

 

If you think of the Australian bush, it’s peaceful and harmonious – you don't need to devote a lot of mental energy to be among it. From an evolutionary perspective, this is ideal. In the urban world, our brain needs to work incredibly hard to process all the stimuli we're surrounded with. Again, evolutionarily speaking, this isn't a good thing – because the brain is constantly searching for danger. Our natural state is to be using indirect attention, absorbing the environment around us. 

 

All this is to say something you likely already know to be true: we feel good, mentally and physically, when we are immersed in nature. I spend a lot of time planting trees and pulling weeds, repetitive tasks in a natural space, and I feel it allows me to access a deeper cycle of thinking. It's funny; we all understand that a computer needs a bit of time to process complex information – yet we don't apply this logic to ourselves. We've got the most effective supercomputer ever created sitting between our shoulders.

From a government level down, we need to quantify the mental benefits that nature provides us. We need to frame these benefits as clearly as we do the physical ones of activities like, say, bushwalking or surfing (or maybe even a polar expedition). 

 

Policy decisions around urban environments need to be informed by the innate human need for nature. Around one million Australians will experience depression in any one year and another two million will experience anxiety. There’s demonstrated evidence that access to natural environments can, in part, alleviate some of this mental health burden. If we can't bring people to green spaces, we need to bring these spaces to them. 

Previously, I’ve worked with urban planners and developers – and they often talk about designing cities for kids. There’s a real cleverness to this insight. Children can't drive cars: in a city for kids, you need to travel from point A to point B by bicycle or foot without crossing busy roads.

 

A city designed in this way will prioritise shared natural spaces that are accessible without the need for people to seek them out. Humans are creatures of habit, and even with access to wild nature within an hour’s drive of many of Australia’s cities – people will still opt to stay within the urban environment.

Unfortunately, we tend to regard flora – all the plants, trees and grasses we share the planet with – as second-class citizens. But they’re the oxygen fixers and nutrient providers for the rest of us. Without flora, there is nothing. 

 

It’s a folly to think of ourselves as separate or distinct from the natural world. Just because we can build environments removed from nature, we don’t escape the need for it. It’s plants – green spaces – that provide us with what we need to survive.