Editors note: I understand that the title to this blog is a bit sensationalist, but if ever a microbiome paper called for a sensationalist headline, this is the one.
Microbiome scientist Marty Blaser (and member of our scientific advisory board) and mathematician Glenn Webb published a remarkable hypothesis last week in Mbio . The hypothesis states that the microbiome is ‘programmed’ to protect us in our youth and reproductive ages, and then kill us in our old age.
First we must consider the enormous influence the microbiome has on our health, both positive and negative, and that we have only explored the tip of the iceberg as to the true impact the microbiome has. Then, we must remember that the microbiome has evolved with us for hundreds of millions of years, from mother to child, and that from the microbiome’s perspective, humans are just a vehicle for reproduction. Finally, we must acknowledge that the microbiome is subject to the same evolutionary principles as any organism or community, and that the laws of nature dictate that it attempts to fundamentally organize itself so as to optimize its population. Once we accept these three things we can investigate how the microbiome could exert its influence on humans so as to improve its population.
A mathematical analysis was performed that showed the most prospering populations of humans, and by extent our microbiomes, occur when young children survive through reproductive ages, but then die shortly after reproductive age. Long lasting, post-reproductive humans can actually diminish the overall population because they drain certain resources. With that in mind it is not a stretch to consider that the microbiome may be dictating this type of population structure. That is, the microbiome prospers when it kills its host (us) shortly after reproductive age, and that it is evolutionarily ‘programmed’ to do just that. This type of population structure occurs in other animals, and the human age structure is unique in the animal kingdom. Humans are pre-reproductive (pre-pubescent) for a longer time than most animals, and then are post-reproductive (senescent) for a much longer time than other animals.
The authors go on to give examples of how bacteria may be dictating the ideal age structure (protecting children and killing senescent humans). We know of many bacteria that exist in children that are protective but then decrease in population into adulthood. In addition there are examples of bacteria, like Helicobacter pylori, that confer protection early in life, but then the very same bacteria can become pathogenic and cause disease later in life. Other bacteria which cause acute infections that kill their host seem only to strike older adults. Finally, the inflammation caused by the microbiome gets worse into old age. In fact, many of the frailties associated with old age can be traced to the microbiome.
It is an interesting hypothesis, and one that the reader should ponder. While it likely can’t ever be proven, this hypothesis supports the idea that it’s a bacterial world, and we are just living in it.