You, Plus Your Closest 100 Trillion Bacterial Friends

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"You" isn't just you. It's actually you plus ... oh, about 100 trillion bacteria living in and on your body. Actually, there's about 10 bacteria for every human cell, so technically, we are all mostly bugs.

The Human Microbiome Project aims to sequence the genetic material of a thousand or so different kinds of bacteria that call your body home:

Humans, he said, in some sense are made mostly of microbes. From the standpoint of our microbiome, he added, “we may just serve as packaging.”

The microbiome starts to grow at birth, said Lita Proctor, program director for the Human Microbiome Project. As babies pass through the birth canal, they pick up bacteria from the mother’s vaginal microbiome.

“Babies are microbe magnets,” Dr. Proctor said. Over the next two to three years, the babies’ microbiomes mature and grow while their immune systems develop in concert, learning not to attack the bacteria, recognizing them as friendly.