Atop a mountain this past summer, backcountry camping for three nights an eight hour hike from civilization, I spent an hour each day keeping up my writing by scribbling narratives of our daily advenutres into my smartphone. This is one of my entries.
day two
Anyone in search of an example of modern evolutionary pressure look no further than the common fly.
Back in the city, like up high in the mountains, flies are ubiquitous.
But unlike the mountains, the cities are filled streets, buildings, parks and coffee shops full of people.
City flies need to be smart and fast. Any fly that is not keenly aware of its surroundings and has not the instinctual inclination to leap into the air and off into the safety of flight is doomed to be swatted by any of a million people. Flies are not be dullards, and any fly born without the inbuilt drive to flee is unlikely to survive long enough to pass on its disadvantageous genome to a future generation.
We will have spent nearly three days up high in the backcountry camping in the mountains where a million variety of insects thrive. In fact even high up above the tree line where even in mid-August patches of snow remain in the share of large rocks, there are so many flies that an adventure-seeker is bound to spend as much time swatting away bugs as admiring the views. And it struck me as curious—though probably less so for the fly which I smacked dead upon my bare forearm—that there must be significantly less pressure, evolutionarily speaking of course, for mountaintop flies to carry a genome that knows better than to get smacked by a human—which a fly may rarely, if ever, see in its short life on the side of a mountain—than for one of its city cousins who encounter humans as a matter of course and have no such luxury as to leisurely investigate a bare forearm on a Friday afternoon.
Nearly every fly I encountered up on that mountain was indifferent to the risk of sudden death carried by my swiftly moving hand. Nearly every fly sat patiently and still as I reached over and snuffed it away.
Smacking a city fly requires speed and agility on the part of a human, but one feels superhuman atop a mountain as the dull flies understand too little what awaits the looming shape and shadow of a hand moving towards them.
Evolution at work.
