companies because of the regulatory hurdles to be overcome. It is much easier to take
a product to market as a food supplement.
18.3.3.1 Non-specific Beneficial Effects of Vaccines
We can also regard the overwhelming evidence for the non-specific beneficial effects
of vaccines as further evidence for the usefulness of parenteral exposure to microorganisms. Many vaccines increase overall survival for reasons that are independent
of the target infection. For example, BCG vaccine saves lives via mechanisms that in
some ways have nothing to do with tuberculosis (Aaby and Benn 2020). Mechanisms are discussed later.
18.3.3.2 The Microbiota of Sweat
We should also consider the natural skin microbiota that our ancestors would have
carried. These would have included ammonia oxidising bacteria (AOB) that are
exquisitely sensitive to alkylbenzene sulfonate detergents, and so are rare on modern
skin. But AOB convert the ammonia in sweat into nitrite and nitric oxide, which are
readily absorbed, and relevant to many physiological pathways (Whitlock and
Feelisch 2009). Interestingly butyrate, which is an important component of body
odour, is a product of lipases from Corynebacteria, Staphylococci, and Micrococci
acting on lipids secreted by sebaceous glands on the skin (Stilling et al. 2016). Was
this also a significant role of our ancestors’ skin microbiota?
18.4 Mechanisms of Benefit from a Green Environment
It is therefore inevitable that we will encounter the microbiota of the natural
environment, and as outlined earlier there are epidemiological indications that
exposure to this microbiota correlates with a reduced incidence of a wide variety
of medical conditions. But why is this so, and are there data that go beyond
epidemiological associations and that offer clear mechanisms to consolidate the
hypothesis? I discuss below the many mechanisms that we can now identify.
18.4.1 Data for the Developing Adaptive Immune System
As already explained when discussing the evolution of the adaptive immune system,
it is a learning system that requires inputs of data to enable selection and expansion
of relevant lymphocyte clones that recognise organisms present in the world into
which the individual is born (Fig. 18.2). Thus, each individual develops and expands
18 Darwinian Medicine: We Evolved to Require Continuing Contact with the. . .
337
a product to market as a food supplement.
18.3.3.1 Non-specific Beneficial Effects of Vaccines
We can also regard the overwhelming evidence for the non-specific beneficial effects
of vaccines as further evidence for the usefulness of parenteral exposure to microorganisms. Many vaccines increase overall survival for reasons that are independent
of the target infection. For example, BCG vaccine saves lives via mechanisms that in
some ways have nothing to do with tuberculosis (Aaby and Benn 2020). Mechanisms are discussed later.
18.3.3.2 The Microbiota of Sweat
We should also consider the natural skin microbiota that our ancestors would have
carried. These would have included ammonia oxidising bacteria (AOB) that are
exquisitely sensitive to alkylbenzene sulfonate detergents, and so are rare on modern
skin. But AOB convert the ammonia in sweat into nitrite and nitric oxide, which are
readily absorbed, and relevant to many physiological pathways (Whitlock and
Feelisch 2009). Interestingly butyrate, which is an important component of body
odour, is a product of lipases from Corynebacteria, Staphylococci, and Micrococci
acting on lipids secreted by sebaceous glands on the skin (Stilling et al. 2016). Was
this also a significant role of our ancestors’ skin microbiota?
18.4 Mechanisms of Benefit from a Green Environment
It is therefore inevitable that we will encounter the microbiota of the natural
environment, and as outlined earlier there are epidemiological indications that
exposure to this microbiota correlates with a reduced incidence of a wide variety
of medical conditions. But why is this so, and are there data that go beyond
epidemiological associations and that offer clear mechanisms to consolidate the
hypothesis? I discuss below the many mechanisms that we can now identify.
18.4.1 Data for the Developing Adaptive Immune System
As already explained when discussing the evolution of the adaptive immune system,
it is a learning system that requires inputs of data to enable selection and expansion
of relevant lymphocyte clones that recognise organisms present in the world into
which the individual is born (Fig. 18.2). Thus, each individual develops and expands
18 Darwinian Medicine: We Evolved to Require Continuing Contact with the. . .
337