Fur, the love of microbes

Without the Sahara desert, the Amazon rain forest could not exist. Surprised? Apparently, it’s true.

The answer, my friend, is blowing in the wind.

Dust.

Mighty desert winds sweep mineral-laden sand into the upper layers of the atmosphere. This dust gently settles over the Amazon basin, supplying important nutrients (especially phosphorous) to the poor soils of the Amazon.

The Sahara has the minerals, but lacks the microbes.

The Amazon has the microbes, but lacks the minerals.

And why, pray tell, does the Amazon have the microbes?

Water.

Microbes need water to survive and procreate. The Amazon has lots of it.

Let’s bring this much, much closer to home – your body.

Imagine the human body as a pipe. The hollow inside of the pipe represents the alimentary canal. The outside of the pipe represents the skin. The pipe itself is made up of muscles, bones and a couple of really useful organs.

The one end of the pipe represents the mouth. The other end is connected to that part of the anatomy your boss will kick when she catches you reading this email during work time.

Note that the inside and the outside of the pipe are connected via both ends. In other words, microbes can freely migrate from the gut to the skin and vice versa. In the middle of the gut, we find a pool of acid – the stomach. This is the most extreme defence we have against organisms entering the body via the mouth. Almost no microbes pass this barrier alive. The few that do, are mostly easily overcome by the Amazon rain forest of microbes waiting for them on the other side of the stomach.

But what about the skin?

Skin is more like the Sahara than the Amazon. Allow me to step back a bit. Biologists separate vertebrate life into five classes: Fish, Amphibian, Reptile, Bird and Mammal. Of these, the first three are covered in scales or naked skin, while birds and mammals have feathers and hair, respectively.

Fishes, amphibians and reptiles live close to water or soil, which are full of microbes – many of them unwelcome. This means the guts of these animals are far less welcoming to microbes. As we’ve seen, microbes are essential to digesting plants and absorbing minerals. Thus fishes, amphibians and reptiles either have to eat animals (since fats and proteins can be digested via enzymes, without microbes) or eat micro- plants (such as algae, which are digestible without microbe action).

Some reptiles escape this bondage to meat-eating by raising their heads high from the microbe-laden ground (think iguanas and tortoises). The rest have to “eat dirt” and meat.

Birds and mammals keep their heads in the microbe-poor air. This means selected microbes can be allowed to enter the gut to assist in the digestion of plants. Despite this advantage, most birds are still seed- or meat-eaters (assuming insects are “meat”, of course). Only once we look at mammals do we find large numbers of plant-eating species. Some, like humans, are omnivorous, which is a most remarkable feat of biological alchemy.

How come mammals manage this dietary switch?

They sweat and they have hair.

Hair traps moisture produced by sweat, which enables microbe cultures to survive on the harsh skin surface. Think of hair as an oasis in the desert.

What is more, certain important skin areas are extra moist, wrinkly and (dare I say it) hairy. Examples are the lips, armpits, areola and groin area. And don’t forget the parts men like to scratch absent-mindedly. Talking of men… By nature the human male is extra hairy at either end of that imaginary pipe we discussed earlier on. Now you know why. Think of men as microbe-rich reservoirs for the human species (but you already suspected that, didn’t you?).

Each of these special skin areas is a mini-rain forest in the middle of the Sahara. Here the right microbes are cultivated and kept in reserve.

All of this wrinkly stuff enables certain gut flora to survive – even flourish – on the skin. This allows microbes to spread between persons (let your imagination run wild), but also – more importantly – to spread from one generation to the next.

All of this to allow you (and your children) to digest SPINACH? CABBAGE? KALE (the four- letter word in superfoods)? You gotta be kidding me.

Here’s the thing: The ability to digest plants helps with food security and survival, especially in dry or cold times. Land cannot support many large carnivores, but it can support massive herds of herbivores. But they need to keep their microbe colonies healthy. One aspect of this is to use hair to “spread the love” within the herd.

But wait, it gets more hairy than this. Check out my next post …

Keep that fur shiny!

Doc Frank