Day 17

First of all, you are not alone. Right now, whether you’re lying in bed or sitting on the beach, you’re in the company of thousands of living organisms—bacteria, insects, fungi, and who knows what else. Some of them are inside you—your digestive system is filled with millions of bacteria that provide crucial assistance in digesting food. Constant company is pretty much the status quo for every form of life outside a laboratory. And a lot of that life is interacting as organisms affect one another—sometimes helpfully, sometimes harmfully, sometimes both.

Which leads to the second point—evolution doesn’t occur on its own. The world is filled with a stunning collection of life. And every single living thing—from the simplest (like the schoolbook favorite, the amoeba) to arguably the most complex (that would be us)—is hardwired with the same two command lines: survive and reproduce. Evolution occurs as organisms try to improve the odds for survival and reproduction. And because, sometimes, one organism’s survival is another organism’s death sentence, evolution in any one species can create pressure for evolution in hundreds or thousands of other species. And that, when it happens, will create evolutionary pressure in hundreds or thousands of other species.
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Outbreaks and pandemics are thought to be caused by antigenic drift, when a mutation occurs in the DNA of a virus, or antigenic shift, when a virus acquires new genes from a related strain. When the antigenic drift or shift in a virus is significant enough, our bodies don’t recognize it and have no antibodies to fight it—and that spells trouble. It’s like a criminal on the run taking on a whole new identity so his pursuers can’t recognize him. What causes antigenic drift? Mutations, which can be caused by radiation. Which is what the sun spews forth in significantly greater than normal amounts every eleven years.

The potential for evolution begins when a mutation occurs during the reproductive process of a given organism. In most cases, that mutation will have a harmful effect or no effect at all. Rarely, a random mutation will confer an advantage on its carrier, giving it a better chance to survive, thrive, and reproduce. In those cases, natural selection comes into play, the mutation spreads throughout the population through successive generations, and you have evolution. Adaptations that confer truly significant benefit to a species will eventually spread across an entire species, as when a strain of the flu virus acquires the new characteristic to go pandemic. But organisms, so the collective wisdom went, only happen upon helpful mutations by chance.

~~Survival of the Sickest--Dr.Sharon Moalem