Looking at Evolution through Germs part: III

Or, screwed, screwed, we are all screwed…Part III

For a second, imagine you’re living in 14th century Southern France, around 1349 AD. This is not only a world without lolcats and gangsta rap, but also one without cotton clothing, chocolate, and a knowledge of how germs are spread.

The last one is particularly important, as a plague called the Black Death is currently sweeping through your town, killing, using the best evidence, about every one in three people. Named because of the blackish color the lymph nodes take when infected with the disease, it spread when rats infected with the disease were bitten by fleas, which then carried it to humans. This was a nasty, nasty way to go.

"Doctor Beak of Rome" an 1656 engraving by Paul Furst. This was the typical uniform of a plague doctor at the time, a sort of medieval hazmat suit. The bird mask holds sweet smelling herbs in the bill in order to keep the smell of death at bay. Seeing as these men were unsuccessful at stopping the plague, it is thought the mask is what gives us the word "quack" to describe unprofessional doctors.

The real question is, why didn’t all of Europe succumb to the plague? The answer again lies in evolutionary biology. Some Europeans had a genetic mutation that made them less likely to get the plague. It is thought that the Yersinia pestis bacterium latched on to a protein found on some people’s cells. Those who had a mutation deleting this protein were much more likely to survive. Six and a half centuries later, a good ten percent of European ancestored people still lack this protein. A cool side effect of this is that HIV uses the same protein, making those with the mutation more adept at resisting AIDS.*

Interestingly enough, evolution and epidemics go hand in hand.

Diseases like smallpox nearly wiped out the Indian tribes when Europeans first set foot on the New World. The reason for this (as well as the reason why the Europeans weren’t wiped out as well) has to do with natural selection. Smallpox had been common to the old world for millennia. Europeans who had genes adept at avoiding smallpox infections were more likely to survive and have children with the same genes. Those who didn’t, died.

Across the pond, the genes responsible for smallpox immunity would have been useless, and therefore not as common. When Smallpox first hit America, as many as 50 million lives were lost. The few Indians that survived were likely carriers of a resistance gene.A scene describing the Smallpox virus racing through the Aztec population. This comes from the Florentine Codex, a story written by unknown native students of Bernardino de Sahagún.

It is thought that germs, not guns or better technology are why we aren’t speaking Aztec.

So the bad news is that germs have been around forever, and some are waiting for a good time to kill millions of us. The good news is that germs aren’t the only things evolving. Humans’ immune systems are constantly evolving new ways to protect us from all sorts of nasty things. This is called the evolutionary arms race, and is a topic for next time.

*The author is saying this is a cool legacy of a long gone epidemic event, not condoning sharing needles or unsafe sex. Don’t be stupid, people.