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Us Vs. Them
"Nature uses only the longest threads to weave her patterns,
so each small piece of her fabric reveals the organization
of the entire tapestry."
Richard Feynman
White blood cells in the immune system function as soldiers on
patrol. They are constantly scouring the corridors of the body,
prowling for intruders. As they move through the veins and
capillaries, they encounter billions of friendly cells and myriad scraps
of flotsam and jetsam that belong to the body itself. Should they make
a mistake and attack these compatriots, the body would be in severe
trouble.
How does the immune system manage to avoid cases of
mistaken identity? The cells of the body have the equivalent of a
uniform--a chemical combination as unique as a human face or a
fingerprint. What's more, invading viruses also have a distinctive
chemical costume. When a white blood cell detects the markings of the
virus, it goes on the attack and sends out signals summoning its legion
of confederates to the assault.1
Uniforms are necessary on the cellular level. They also prove
indispensable to human society. Margaret Mead says every human
group makes a simple rule: thou shalt not kill members of our gang,
but everyone else is fair game. According to Mead, each group says
that all humans are brothers, and declares that murdering humans is
out of the question. But most groups have very strange means of
defining who is human.
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