Healthy People in Modern Cities

Science and technology have always been and will continue to be the driving forces of developments in societies, especially those that address the questions of where and how we live. The modern cities of today, as well as their architecture and infrastructures, are the most visible examples of scientific and technological progress.

Medicine is no exception to this progress, especially in light of the advances made in the fields of genetics and genomics. About ten years ago, an international effort to sequence the human genome allowed the first insights into our hereditary set up – and the cost of this international project was enormous. Now, with new-generation sequencing methodologies, genome sequencing has become a routine laboratory technique, and at a relatively low cost.

New scientific fields, namely ‘genomic and molecular evolution’ and ‘evolutionary medicine’ (also known as Darwinian medicine), have been made possible by modern sequencing technologies, and are opening up new vistas in science and medicine. Today all model organisms and important steps in the path of evolution have been sequenced or are available for detailed molecular analysis. We can now start to answer questions about how life emerged 3.5 billion years ago and where we, homo sapiens, come from. We can begin to understand our genomic history, and know more about the appearance of modern man in Africa and how he colonised the world over the last 100,000 years. It is evident from this research that our genes and important functions have been conserved throughout billions of years of evolution. We know that the human body is a living archive of the origins of life. The more important specific genes are for biological functions, the better and longer they have been conserved in evolution.
Modern genome research and the new concept of evolutionary medicine open up completely new avenues to a better understanding of the basis of health and disease. In addition to asking proximate questions about how biological mechanisms of a disease are best understood, diagnosed and treated, we can also now investigate the ultimate question, namely: why do we get sick?

With our evolutionary ‘old’ biology we are living in a completely new and fast-changing (mostly artificial) human-made environment: the city. No longer are we labouring hard to harvest a scarce living like in the stone age. No longer are we running away from big animals to avoid being killed, or chasing smaller animals in order to provide food for our families. Much of modern urbanised society is now dependent on industrially manufactured food, ordered by smart phone from the department store and delivered straight to our door. We eat too much, and consume foods that are too salty, sweet and full of fat. Some of us lead sedentary lives, and make a living by sitting in front of a computer all day and moving knowledge electronically to far distances around the world. Energy is provided from the plug and no longer burnt by exercising one’s musculoskeletal system.

Diseases of civilisation

We are thus facing a new challenge. In urbanised life, and in industrialised countries, new common diseases are emerging: obesity, diabetes, cardiovascular diseases, hypertension, musculoskeletal diseases, osteoporosis, mental health problems, depression and so on. The underlying cause of these ‘diseases of civilisation’ is that our modern lifestyles, which are manifest in our cities, are not in tune with our biological heritage.

For the well-off in our globalised world, constantly sitting around became an attribute of an existence where physical work was no longer necessary, a result of the technical progress and affordable motorised mobility for a broad sector of the population, a development which first emerged in the twentieth century. This century was one characterised by reduced physical work and physical mobility – facilitated by high-tech cars and public transportation for the masses, as well as by more mundane innovations such as electric corkscrews and battery-powered pepper mills, for example. This is historically comprehensible since, until recently, relatively hard physical work was the standard, and the aspiration to afford some comfort in daily life was obvious and wide-spread.

Meanwhile it has become clear that such comfort, which some can afford due to technical progress and unequal economic growth, can have negative consequences for our health. Hundreds of millions of humans no longer challenge their bodies physically and this, in turn, leads to functional impairment. Thinner, weaker muscles, whose abilities to burn carbohydrates and fat is lessened, as well as fragile bones, increased resistance to insulin and an increase in heart disease, are threatening those who lead an idle existence. From an evolutionary perspective the bodies of physically inactive humans are in a highly exceptional state. But, because of our urbanised lifestyles and physical inactivity, it is not our external stature that will be affected so much as our inner well-being and health, and these stresses will frequently go unnoticed.

Therefore the discrepancy between our biological heritage and modern lifestyles makes us ill. The gap between evolutionary ‘old’ body functions, on the one hand, and modern lifestyles in new urban societies, on the other, results in the above mentioned ‘diseases of civilisation’. They are the biggest burden on health care systems within modern knowledge-based societies. Evolutionary medicine makes use of these new insights for the research, diagnosis, treatment and, most importantly, prevention of diseases.

A large part of our modern civilisation depends on the close collaboration and exchange of ideas between peoples, a necessity enhanced by our fast-urbanising globe. Moving back to the countryside, as some romantic ecologists propose, is not a realistic solution for solving today’s health problems. The great achievement that makes humans unique and which explains our special path in the animal kingdom beyond biological evolution is not only our coexistence in dynamic societies but also, and primarily, our creative cooperation based on a division of labour.

New infectious diseases

The city is a stimulus and source of continuous progress and development of new technologies. The city is the place where humans can realise cooperative and collaborative lifestyles. But history also shows us that the development of new settlements and cities was followed closely by the rise of new diseases. At the end of the last ice age, around 10,000 years ago, the world flourished. Humans changed from being hunter-gatherers to building and settling down in villages and towns and developing farming and cattle-breeding technologies. They exploited new food sources, they domesticated the first plants and animals, and the number of the people on the planet increased. By actively planning their environment at an ever-increasing rate not only did human behaviour change but also, without us being aware of it, the behaviour and opportunities of micro-organisms. This is the moment when infectious diseases were born in evolution.

All kinds of animals, from mosquitos to rats, were attracted by the fields, grain stocks, waste and faeces that were mounting in permanently growing settlements, villages and cities. Infectious microbes and their carriers, bigger animals, including mice, rats and humans, found their paradise: protection from predators in the city and a wide range of ‘food’. Along with them came many pathogens, which discovered humans as a new host. As this host reproduced more rapidly, their future was secured. Before major human settlements and urbanisation, there were simply too few people living together to keep an infectious agent alive. People lived in quite small units and continually moved from one place to another. If there was a pathogen that developed and survived by transfer from human to human, the whole group would eventually be wiped out and the pathogen itself reached, literally, a dead end. Or natural selection ensured that only a few very resistant individuals survived, and that this resistance was passed down to their offspring and gave the microbe no further chance to reproduce.

The success of deadly epidemics caused by viruses or bacteria that decimated the population periodically in history was only possible under the condition of settlements and the development of larger stable communities. With the development of urban civilisation, infectious and virulent microbes no longer meet dead ends, but move from host to host, surviving and multiplying happily. In cities, even the most deadly viruses and microbes can survive, since in these large, densely packed populations, there is always a new host to infect. With humans now travelling as much as they do, the whole world population is a potential host for infectious agents, and thereby the pool of pathogen carriers is ever-increasing.

Modern medicine has developed strategies to counteract these new and unique threats brought about by urbanisation: standards of hygienic and other implementations, for example, which aim to control major infectious diseases. Aside from vaccines and antibiotics, modern water and wastewater management systems are crucial for survival in the city and for the fending off of diseases. These same systems, however, lead to extreme vulnerability in humans if they become contaminated by disease. Major epidemics, such as SARS, EHEC and Bird flu, and the attention paid to them internationally, attest to the reality of the threats and the possible social and economic costs to humans. If concepts for healthier cities are going to hold ground, they need to take account of these new insights from evolutionary medicine.

Disease prevention is the name of the game

In many instances we know why we get sick and how to avoid becoming sick. It is more effective and cheaper to prevent a disease than to treat it, which is why architects, city planners, politicians and medical practitioners will have to collaborate more effectively if they want to learn from each other and build better and healthier cities. Cities are places of collaboration and cooperation. We have to make better use of them if we want to improve our future.

The help of Thilo Spahl, Berlin, in preparing and reviewing the manuscript is gratefully acknowledged.

The help of Thilo Spahl, Berlin, in preparing and reviewing the manuscript is gratefully acknowledged.

Detlev Ganten is President of the World Health Summit and Chairman of the Foundation Board of the Charité Foundation Berlin, the Board of Trustees of the Max Planck Institute of Colloids and Interfaces as well as the Max Planck Institute of Molecular Plant Physiology.