Why are we more afraid of snakes than of cars? Of back-alley murder than diabetes? It's evolution. Evolution shapes bodies. It sharpens teeth and reflexes, produces natural camouflage and intimidating plumage. It also shapes minds. Just as the tick is naturally attracted to the smell of mammalian sweat, humans are born with a set of emotional orientations formed over millions of years to help us pass on our genes.

But with such rapid industrial and technological advances, our evolutionary feels haven't had the chance to catch up. Humankind did most of its evolving in primeval grasslands. Our current environment and circumstances are quite different, so our instinctive fears are not especially well-attuned to the things that actually pose the greatest threats. Gordon Orians is a professor emeritus of biology at the University of Washington and author of Snakes, Sunrises, and Shakespeare. We reached out to him to find out how modern humans inherited an innate sense of fear that is deeply shaped by the things that commonly killed our ancestors and to compare those threats to the things that are much more likely to actually kill us now.

Evolving fear

If something kills you over and over again for thousands of generations, evolution will select for any instinct or behaviour that motivates you to spot and avoid that thing.

Take the example of snakes. Snakes are primates' oldest predators. They've been killing people since before people were people. And this long and unpleasant experience has yielded long-lasting changes to our genes. Our vision has evolved to spot their shape and patterns against even before we're consciously aware of them and our neurons activate a fearful reaction. Startling at the sight of a snake, is a nearly universal human response seen even in even babies. And we're not alone in this. In his book, Orians explains that both lab-raised primates and North American ground squirrels with no previous exposure to snakes nonetheless react very strongly to them. Of course, these legless reptiles aren't our only innate fear. We've inherited a deep emotional connection to a lot of the main causes of death of our ancestors.

Here's a short list of some things that evolution has made us afraid of along with some things that, empirically speaking, are more likely to finish us off.

What evolution makes you scared of versus what might actually kill you

Evolution makes you scared of: Animals. We're naturally attuned to the dangers posed by animals, especially our natural predators. Snakes are a major one, but humans are also instinctively afraid of spiders, hunting cats, and herbivorous animals that may have posed a danger. Just trying to avoid getting hurt by these animals has shaped our instincts and physical senses.

What actually kills you: Cars. There were 300 reported snake bites in Canada last year, with zero resulting deaths. By comparison, there were about 160 000 traffic accidents in Canada in 2016, killing nearly 2000 people. Yet we board these death traps with blithe confidence. Orians himself has tried and failed to emotionally assimilate the danger posed by auto travel: "Probably the most dangerous thing I've done in my life is drive a car. And I've tried, when I get behind the wheel, to make myself aware of that and I just can't do it. I get into the car, turn on the ignition, and I'm emotionally on a power trip, not afraid."

Evolution makes you scared of: Pus, corpses. Disease was a major killer of our ancestors and this led, says Orians, to the evolution of a kind of "intuitive microbiology" that makes humans naturally averse to likely sources of infection. A revulsion or fear of pus and rotting flesh seem to be hard-wired in us.

What actually kills you: Sugar, alcohol, cigarettes. In Canada, you're highly unlikely to get enough corpse-exposure to catch anything from one, and if you do, whatever you get will probably be treatable. However, illnesses related to long-term choices in diet and consumption are leading causes of Canadian death. A can of pop may not look as scary as a dead body, but it's far more likely to shorten your life.

Evolution makes you scared of: Strangers. Humans have a deep-seated sense of stranger danger. In Snakes, Sunsets, and Shakespeare, Orians writes "Throughout human history, we have distrusted people outside our clan, our tribe. … we believe strangers will do us harm. Why? In deep time, hominids outside the family group were likely to be a raiding party." Today, in Canada, homicide accounts for only 0.2% of all deaths. Yet our brains are obsessed with it. As a culture, we gobble up stories about dangerous strangers, from real-life serial killers, to horror-flick fictions. In doing so, we're enjoying in an emotional charge built up by the murder of generations of our ancestors.

What actually kills you: Your friends, your family, you. Suicides are the cause of ten times more deaths than homicide in Canada, in some cases pointing to problems with mental health as the danger to pay attention to. And in the rare event that we do murder each other, it's generally someone we know. Around 86% of Canadian murders are committed by someone known to the victim, often a family member or intimate partner. Stranger-murder is comparatively rare, so worry less walking home through the alley, and more about what happens when you get there.

Evolution makes you scared of: Immediate short-term threats. Orians told us that "our nervous system, evolved in the African savannah, deals magnificently with things that are short-term and small-scale." Human fear is stronger to the extent that the danger is nearer. We're neurologically wired to escape snake attacks, and can even adapt our behaviours to account for changes in season. Unfortunately, the more distant the threat in time, the less it pulls our emotional triggers.

What actually kills you: Climate change (and other long-term threats). According to Orians, the biggest threats facing humanity are environmental ones. Threats to our environment are so dangerous because of their enormous consequences and because they're likely to slip by our natural detection system. "It's easy to say we have a global problem and have to think globally, but that doesn't really affect the nervous system." Long-term threats can be enormously dangerous but don't have any purchase on our evolved emotions. He believes that the best way to motivate people to act on climate change is to link it somehow to local actions with visible tangible results.

Clifton Mark is a former academic with more interests than make sense in academia. He writes about philosophy, psychology, politics, and pastimes. If it matters to you, his PhD is in political theory. Find him @Clifton_Mark on Twitter.