Stacks Image 181
Stacks Image 1964

IMPORTANT new paper on health, microbiota and the natural environment :-

Flandroy L, Poutahidis T, Berg G, Clarke G, Dao M-C, Decaestecker E, Furman E, Haahtela T, Massart S, Plovier H, Sanz Y, Rook G.

The impact of human activities and lifestyles on the interlinked microbiota and health of humans and of ecosystems.

Science of the Total Environment. 2018;627:1018-38.
Stacks Image 1973

New LANCET paper on evolution and microbiota.

Rook G, Bäckhed F, Levin BR, McFall-Ngai MJ, McLean AR.

"Evolution, human-microbe interactions, and life history plasticity."
. (2017), Jul 29 390(10093):521-530. doi: 10.1016/S0140-6736(17)30566-4. Epub 2017 Jul 27.

Abstract. A bacterium was once a component of the ancestor of all eukaryotic cells, and much of the human genome originated in microorganisms. Today, all vertebrates harbour large communities of microorganisms (microbiota), particularly in the gut, and at least 20% of the small molecules in human blood are products of the microbiota. Changing human lifestyles and medical practices are disturbing the content and diversity of the microbiota, while simultaneously reducing our exposures to the so-called old infections and to organisms from the natural environment with which human beings co-evolved. Meanwhile, population growth is increasing the exposure of human beings to novel pathogens, particularly the crowd infections that were not part of our evolutionary history. Thus some microbes have co-evolved with human beings and play crucial roles in our physiology and metabolism, whereas others are entirely intrusive. Human metabolism is therefore a tug-of-war between managing beneficial microbes, excluding detrimental ones, and channelling as much energy as is available into other essential functions (eg, growth, maintenance, reproduction). This tug-of-war shapes the passage of each individual through life history decision nodes (eg, how fast to grow, when to mature, and how long to live).

Is the term “Hygiene hypothesis” now obsolete?

Domestic hygiene is not causing the poor regulation of our immune systems.
Other lifestyle changes described in these pages are to blame.

Click here to download a new paper reviewing this topic.

New review paper on the Psychiatry page. “The Microbiota, Immunoregulation, and Mental Health: Implications for Public Health”. Curr Envir Health Rpt (2016) 3:270–286. Download here or from psychiatry page.
New material and papers in the Green Space and Interviews pages, and a new Microbial Biodiversity page
New PNAS paper in the PSYCHIATRY page: immunising with an organism from the environment can oppose effects of stress.

This site provides rapid access to our latest thinking on the "Old Friends mechanism", a reformulation of the hygiene hypothesis as a crucial branch of "Darwinian" or "Evolutionary" medicine.

The pages that follow contain mostly recent publications, together with their abstracts, and links that will enable most of them to be downloaded.... when that is not possible, email me and I will send a copy if I can.

We discuss the evolutionary theory and immunological mechanisms behind the Old Friends mechanism, and point out the implications for human health and wellbeing in rich developed countries.

The current emphasis is on reduced stress resilience and the increased prevalence of depression in modern city-dwellers. We argue that this is at least partly secondary to defective immunoregulation attributable to the "Old Friends" mechanism.

A new extension of the Old Friends mechanism considers its role in the beneficial effects of living close to Green Spaces. See my recent review of this topic in Proc Natl Acad Sci USA (PNAS).... go to the Green Spaces page

There is also a new link to BBC Active. They offer educational BBC television programmes for use by Schools and universities. I took part in a programme in the BBC’s Horizon series with the title “Allergies- Modern Life and Me”. See more about this on the “Interviews” page of this site.



The pages first describe the "Old Friends" mechanism, and why this Darwinian concept usefully expands and corrects the original hygiene hypothesis, and increases its explanatory power in several clinical domains.

Then the site deals with the implications of faulty immunoregulation for psychiatry, and in particular for depression and stress resilience. It is postulated that one reason that depression is increasing is a reduction stress resilience in rich countries that has an immunological basis

Several of the papers refer to autoimmunity, but this page shows one that deals almost exclusively with this topic, and attempts to reconcile the many hypotheses about the recent increases in autoimmune disorders.

A failure of immunoregulation can lead to cancer, and also drive the cancer after it has developed. Inflammation drives mutation and provides angiogenenic factors, and tumour growth factors. The increase in the incidence of some cancers (such as prostate) parallels the increases in other chronic inflammatory disorders.

Exposure to green spaces improves physical and psychological health. The Old Friends mechanism provides a mechanism that can be documented by physiological measures relating directly to the disorders from which green spaces protect us. We may have evolved to need psychological input from the natural environment. But just as important, our immune systems have evolved to require inputs from biodiversity of the natural environment.

There are several recent interviews, all on the topic of the "Old Friends" mechanism and its clinical implications

The book "The Hygiene Hypothesis and Darwinian Medicine" gathered together experts in different fields, to discuss the potential role of failing immunoregulation in the aetiology of chronic inflammatory diseases of different organ systems.


Meanwhile, here is a link to those of my publications that are listed in PUBMED. Many of them can be downloaded free of charge by anyone.

This link goes to the UCL site

Prof Graham A.W. Rook, BA, MB, BChir, MD.
Centre for Clinical Microbiology
UCL (University College London)