While literally naval-gazing, one of the interesting things I've been mulling over is that human bodies are made up of a multitude of creatures, working symbiotically together.
This idea has fascinated me for a long time, and was the impetus for my Symbiosis painting, recently featured on The Eloquent Atheist. Only recently did I come across an explanation for where the microflora largely come from.
Most of the symbiotic bacteria are transferred to infants from the mother, mainly during birth, and from the breast-feeding and foodstuffs to follow. I thought this topic would be an interesting counterpoint to these life drawings I did of a model at the Toronto School of Art last spring. Less so simply because the model was female; moreso because of every move, every pose we all make every day, we are a multitude of organisms working together, resting together and just being together.
While reading Daniel Dennett's Breaking The Spell, he makes another arresting point. Not only do you have an entire ecosystem of bacteria in your body, on your skin, "your body is composed of perhaps a hundred trillion cells, and nine out of ten of them are not human cells! (p.86)" The important point is that they are not transmitted genetically.
Some people say we are really all alone trapped inside our own minds and bodies. We seldom think of what organisms we share our bodies with, and that our whole lives, the ecosystem living within us and on us, is still evolving.
Bacteria can evolve at a prodigious rate; and for men, we carry them around, populations evolving as we subject their environments to espresso and fine cheeses, beer and pizza, until our whole system collapses. For women, it goes further. Women pass on their evolved-since-birth microflora to their children, when they give birth. As Dennett points out (p.86 again), since it is not a genetic inheritance, and so a surrogate-mother still gives her infant a large portion of its future health during the minutes of birth.
In an interesting turn in one of my favourite sci-fi series, a few characters in David Brin's Heaven's Reach , part of the Uplift Storm trilogy, find themselves becoming symbiotically entangled not only with other similar, oxygen-breathing aliens, but also with the mysterious hydrogen breathers that live inside gas giants. All of them are swallowed up, to transcend into being part of a new organism known as 'Mother'.
There are more interesting things to learn about this subject. Check out the Wikipedia entry, and more at ScienceBlogs.
Amazing. No person is an island; but we are all ecosystems.