A great poet once said that no man is an island. He was more right than he could possibly have known. Each one of us is not an island, but a community, an ecosystem, if you will. Each one of us has a number of creatures who depend on us for a meal, or a place to live. Most people despise these dependants who live off us as disease carrying parasites and seek to get rid of them at any cost. Roger M. Knutson might disagree. Roger Knutson is a biologist who has written Furtive Fauna, a field guide to the creatures that live on us or near us. Knutson asserts that our dependants are more to be pitied, even respected, than hated. After all, the human body is not exactly an easy environment to live on.
In Furtive Fauna, Professor Knutson catalogs the many creatures that live with us. He starts with the occasional visitors, like ticks, flies and mosquitoes who like to drop by for a quick snack. He then moves on to some of our neighbors, bedbugs, fleas, and others who live in our clothes and bedding. These neighbors, like any good neighbor, often visit us, and like good hosts, we provide them with food and shelter. Then, there are our friends and companions; lice and mites, who like to live with us and keep us company. You can never feel lonely as long as you know you have mites living on you. Finally, we have the friends that are too small to see, like bacteria. They are everywhere and we could not live without them.
Roger Knutson’s descriptions of the various furtive fauna are brief, humorous, and fun to read. You may never come to love the little beasts that live off you, but after reading Furtive Fauna, you will never think of them in quite the same way.
No man is an island entire of itself; every man is a piece of the continent, a part of the main; if a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as any manner of thy friends or of thine own were; any man’s death diminishes me, because I am involved in mankind. And therefore never send to know for whom the bell tolls; it tolls for thee.
Though he had it slightly wrong. If the latest research in biology is any indication, we are, each one of us, a continent, perhaps even a world in ourselves. That is the impression I got when I read this article in The Economist.
The traditional view is that a human body is a collection of 10 trillion cells which are themselves the products of 23,000 genes. If the revolutionaries are correct, these numbers radically underestimate the truth. For in the nooks and crannies of every human being, and especially in his or her guts, dwells the microbiome: 100 trillion bacteria of several hundred species bearing 3m non-human genes. The biological Robespierres believe these should count, too; that humans are not single organisms, but superorganisms made up of lots of smaller organisms working together.
It might sound perverse to claim bacterial cells and genes as part of the body, but the revolutionary case is a good one. For the bugs are neither parasites nor passengers. They are, rather, fully paid-up members of a community of which the human “host” is but a single (if dominating) member. This view is increasingly popular: the world’s leading scientific journals, Nature and Science, have both reviewed it extensively in recent months. It is also important: it will help the science and practice of medicine
The microbiome does many jobs in exchange for the raw materials and shelter its host provides. One is to feed people more than 10% of their daily calories. These are derived from plant carbohydrates that human enzymes are unable to break down. And not just plant carbohydrates. Mother’s milk contains carbohydrates called glycans which human enzymes cannot digest, but bacterial ones can.
This alone shows how closely host and microbiome have co-evolved over the years. But digestion is not the only nutritional service provided. The microbiome also makes vitamins, notably B2, B12 and folic acid. It is, moreover, capable of adjusting its output to its host’s needs and diet. The microbiomes of babies make more folic acid than do those of adults. And microbiomes in vitamin-hungry places like Malawi and rural Venezuela turn out more of these chemicals than do those in the guts of North Americans.
The microbiome also maintains the host’s health by keeping hostile interlopers at bay. An alien bug that causes diarrhoea, for instance, is as much an enemy of the microbiome as of the host. Both have an interest in zapping it. And both contribute to the task. Host and microbiome, then, are allies. But there is more to it than that. For the latest research shows their physiologies are linked in ways which make the idea of a human superorganism more than just a rhetorical flourish.
So, each one of us is not just a single entity, but a whole community of microbes. I’ll never feel lonely again. Meanwhile, we should all be good to our bacteria, they are our closest friends.
Every biology textbook that I have ever read stated that women are born with all the eggs they will ever have and their ovaries do not produce any more. It turns out that every biology textbook that I have ever read is wrong. From Scientific American.
A study led by Jonathan Tilly of the Massachusetts General Hospital overturns the decades-long idea that women are born with all the eggs they will ever have. It reports that women of reproductive age carry ovarian stem cells, meaning that they can produce new eggs. Tilly’s team, which made a similar finding in mice in 2004, also discovered that mouse eggs derived from such stem cells can indeed be fertilized.
Our colleagues at Nature Medicine, which is publishing the paper today online, created this four-minute video explaining the results. (Scientific American is part of Nature Publishing Group.)