The world is dominated by single celled organisms.
Whether one is talking about total biomass or number of unique species, single celled organisms rule!
This is not necessarily obvious as most of the living organisms that we encounter - trees, people, dogs, and such - are large and multicellular. This biases us into thinking that most of life is the same way.
But the 100,000 or so bacteria that are living on each square centimetre of your skin would beg to differ. They and their cousins are everywhere. They are just hard to see.
Stephen Jay Gould once argued, in one of his science columns, that despite the fact that there are nearly one million species of multicellular organisms named (and 80 per cent of those are arthropods), there are a great many more that are not multicellular. Some scientists have gone so far as to claim that 90 per cent of all species on this planet are bacteria.
We live in the Age of Bacteria and always have.
For much of the past 200 years, we have associated bacteria with disease, and rightly so. Some of the deadliest toxins known to science are produced by bacteria. One tenth of a microgram of botulism toxin - produced by the bacterium Clostridium botulinum and related species - is enough to kill an adult.
Other bacteria are responsible for pneumonia, meningitis, and necrotizing fasciitis or flesh eating disease along with numerous other diseases. Indeed, the common flu is most often simply a case of mild food poisoning induced by bacteria.
Our war with bacteria dates backs to the mid-19th century and Louis Pasteur. The realization that proper hygiene, pasteurization of food products, proper care and treatment of water and sewage, isolation of the ill, and a host of other practices drastically reduced the levels of disease in the general population.
We learned to sterilize our immediate environment as much as possible. Indeed, we have become to some extent germ-o-phobic.
But we also need bacteria and not just the ones living on our skins. We need bacteria living in our guts.
It is called the human microbiome and it plays a critical role in digestion of our food and immunity to disease. A healthy microbiome has been linked to reduced levels of cancer, obesity, and a number of other health related issues in our modern age.
Unfortunately, no one is exactly sure what constitutes a healthy microbiome. Indeed, the bacteria which live in our digestive tract in a symbiotic relationship are not inherently good. They can be helpful in our gut but deadly in other parts of the body.
Furthermore, research on the human microbiome has been biased towards Western societies, based heavily in Europe and North America. Perhaps not surprisingly, in other parts of the world, the microbiome is significantly different.
In particular, scientists have studied the microbes found in hunter-gatherers from around the world and found they differ significantly from the Western guts. They are generally more diverse.
This does not necessarily mean healthier. The microbiomes of the Hadza, hunter-gatherers from Tanzania, contain almost no Bifidobacteria, which is a strain generally viewed as healthy by most researchers. It constitutes about 10 per cent of the organisms found in a typical Western intestine.
They also found more Treponema, which is a strain associated with syphilis and yaws.
However, recent results on Peruvian hunter-gatherers who lead traditional lifestyles also showed higher levels of Treponema but, in this case, the strains were significantly different from those which cause disease.
These microbes are more closely related to the bacteria that allow animals to digest carbohydrates.
These are the same strains found in the Hadza and some non-human primates. They are totally absent from most industrialized populations. They are part of the lost microbiomes and no one is exactly sure what the consequences have been.
Having intestinal bacteria capable of breaking down or digesting carbohydrates may have helped our ancestors deal with a diet rich in carbohydrates. Losing this ability might be part of the picture when it comes to dealing with obesity. Then again, there could be all sorts of other factors at play.
Ideally, to understand all of the important factors you would need to study a large number of groups of people leading traditional lifestyles. Elise Morton and co-workers from the University of Minnesota, for example, have been studying the microbiomes of four groups in Cameroon. Their results indicate substantial differences in the guts for each group.
In particular, they found high levels of a parasitic amoeba leading to questions about the influence other organisms have on the communities we have in our intestines. But no one knows exactly how these relationships work.
Whether they are good or bad is still up in the air.
The only thing that is really clear is that there is still much more to learn about the dominant life forms on Earth.
