Why isn’t evolution erasing roadkill?

I live in the suburbs, so dodging roadkill on the way to work is a daily fact of life.  I’m also an unbridled dork, so I can’t help but wonder when I pass the poor victims when evolution is going to kick in and give these guys the sense to stand back from the highway, or come up with some other novel deterrent.  Then I put my reasoning cap back on and remember that evolution is a slow and gradual process, grinding out over vast stretches of geologic time, and that even beneficial changes can be diluted in a large population and not take hold. Maybe our vehicular death dealers are just too new on the scene to have yet prodded any progress.

But it’s not like we haven’t observed selection in action, often times resulting from our own deeds.  The easiest example is the adaptation of bacteria to resist certain antibiotics, a topic discussed at length here on WDTM?  Bombing a bug with drugs is really no different than any other environmental pressure, and those bacteria that just happen to be better equipped to weather the medicinal storm are the ones that live to repopulate the world with more robust beasties.  Bacteria aren’t the only creepy crawlies to get a boost from our well-intentioned eradication efforts, as the recent bedbug plagues in New York City and elsewhere demonstrate.  A March study in Scientific Reports observes that 14 protein-coding genes were “overexpressed” in the heartiest populations, preventing or slowing the absorption of pyrethroid, the most common pesticide used against them.

On a macroscopic level, a group of common mice in Germany have become resistant to the poison warfarin as a result of a horizontal gene transfer from the non-native, human-introduced Algerian mouse.  The unintentional poisoning of the Atlantic tomcod thanks to General Electric’s decades of inconsiderate PCB-dumping into the Hudson River has caused the feisty fish to develop a way to keep the chemical from binding to its cells.  And don’t forget the textbook peppered moth example which, despite flaws in the original methodology that have been corrected in later experiments, continues to show that the darkening of tree bark by industrial soot helped the varieties with more melanin blend in better and avoid the notice of predators, drastically decreasing the population of the their lighter colored brethren.


So what gives, guys?  I know there isn’t camouflage that would conceal certain raccoons from cars, but knowing that major changes can take place within a few generations thanks to our (often unhealthy) influence, where’s the roadkill resistance?  Charles Brown of the University of Tulsa may have found an example!  He describes in a Current Biology paper how his taxidermy hobby led him to notice that fewer and fewer cliff swallows were being hit by cars over the past 30 years, and further research showed that the ones who do meet their untimely ends have longer wingspans, on average, than the rest of the populations.  It might be that shorter wings make the birds more maneuverable, or maybe they’re just smartening up and staying away.

Evasive maneuvers!  From wired.com

In either case, that’s a system working and more evidence that some organisms can adapt rapidly to selective pressure, even when it’s unnaturally introduced by us.  That’s not a reason to continue our bad behavior, though.  For example, the buffed up Atlantic tomcod may be resistant to its surrounding toxins, but the things that eat it (like HUMANS) aren’t and can subsequently still get sick.  Plenty of other fish species in the Hudson have suffered.  Pest resistance obviously isn’t something we want to encourage, either.

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