When I wrote that book I wrote about sex, I did a lot of thinking about our species’ tendency to think we’re on an upward climb toward perfection. More than that: We tend to think we’ve just about reached it. Humans love gazing down the proverbial slope of time to pity and mock any ancestors stuck at a lower elevation. We tell ourselves stories of previous generations that solidify their ignorance and our cleverness (while also, naturally, wringing our hands over the worrying behavior of wayward youths destined to supplant us).
When things are good, we believe we can thank the great machine of society for hoisting us higher up the mountain of progress. When things are bad, we are certain we must be living in the end times; we are sliding down a slippery slope, and soon all will be lost.
Darwin added the omnipotent hand of natural selection to our climbing rig, and the genomic age has given us another metric to point at; we now have a record of the changes that helped our lineage rise above the ones that didn’t make it. Even as these investigations actively destroy old narratives of supremacy—like the belief that our species bested Neanderthals into oblivion—we cling to the idea that we’re moving toward something. Sure, we screwed Neanderthals instead of killing them, but that means only their best genes survived within us.
But there’s no such thing as a good gene. There are genetic quirks that can help or hurt us in equal measure, depending on what configuration we get them in and where and when the randomness of the universe spits us out to live our lives. We carry the scars of our ancestors’ traumas and triumphs in our DNA, but that doesn’t mean we carry the best of them—or that their best will do us any good in 2022.
A few weeks ago, researchers published the most extensive study to-date on how the Black Death, which may have killed as much as half of Europe’s population during the 1300s, impacted the genes of humans alive today. They extracted DNA from the remains of a mass grave known, apparently, as “the lasagna of Black Death”—so dubbed for the care and precision with which so many dead were laid to rest there during 1348 and 1349, when the plague caused by Yersinia pestis was at its peak. In comparing those genomes to humans who died a bit before and to those who died a generation or two after, they were able to identify genes that seem to have protected Europeans from the ravages of plague.
For one gene in particular, the group went so far as to test how the presence or absence of the plague-related variant could change a body’s reaction to Yersinia pestis. With two copies of the mutation, they showed, resistance to plague bacteria was significantly increased.
But evolution is not linear, and humans did not overcome the Black Death by taking one step closer to genetic perfection. The mutation, which works by doing the equivalent of putting your enemy’s head on a spike so the townspeople know to lose their shit if his twin brother ever shows up, is also associated with an increase in autoimmune conditions. This makes sense: Despite the many headlines and influencer posts promising to “boost” your immune system, a hyper-vigilant biological defense system is prone to cause its own host of horrors. A lot of random guys can look pretty similar to a bloated head on a spike, especially when tensions are high.
These things happen. Sickle cell trait is a brilliant evolutionary tactic against malaria, while sickle cell anemia causes excruciating pain and life-threatening complications. Our brains are so big that our births are gruesome and our psyches are fragile. Evolution doesn’t take requests. It doesn’t strive for perfection.
We’re not heading for the top of a mountain. We’re walking through a world full of hills and valleys.
The Black Death must have felt like the end of the world. How do you recover from watching a third of your neighbors die brutally? We must imagine that many of our ancestors simply did not, but survived anyhow. And the world kept turning, and one day researchers would casually offer the hypothesis that this apocalypse had made our species stronger by weeding out so many of the “frail.” It’s a sentiment not dissimilar from many of the governmental and personal reactions to COVID, with many decisions seeming to hinge on the question of which people it is good and right to keep alive.
We’ve indisputably made progress since the Black Death in at least one regard: We have much more power than our 14th-century ancestors did in determining who gets to survive the end of the world. We also have unprecedented control over how humans will live in 700 years. But we can really only be sure of two things: First, that our distant progeny won’t be any closer to perfect than we are. And second? They’ll think we were a bunch of foolish, backwards apes—and they’ll probably hate us for leaving them stuck with whatever the 28th-century equivalent of Lupus is.