Thinking Beyond Science

In the popular imagination, global warming spells doom for cold-loving species—and for good reason. The Arctic’s perennial sea ice now covers just half the area it did thirty years ago, and it could vanish entirely in another thirty. Animals like ringed seals and polar bears, utterly dependent on that ice, face a dire future as it melts away.

But here’s the twist: the real biodiversity hotspot—the tropics—might be more resilient than we think. Why do more species thrive there? One theory says the evolutionary clock ticks faster in the heat. Just as farmers harvest more crops per year in lower latitudes, tropical organisms churn out more generations. More generations mean more genetic mutations, boosting the odds of new species emerging.

A second idea points to tropical species’ pickiness. Temperatures there stay remarkably stable, so these creatures evolve narrow thermal tolerances. Even tiny climate shifts—like those from a nearby hill or valley—become impassable barriers, splintering populations into isolated, diverse groups.

Time plays a role too. The Amazon rainforest, or something like it, has endured for millions of years—predating the river itself. Diversity has had eons to pile up. Contrast that with Canada or New England: just 20,000 years ago, ice a mile thick smothered them. Every tree in Nova Scotia, Ontario, Vermont, or New Hampshire today is a recent migrant. Alfred Russel Wallace, Darwin’s rival and co-discoverer of natural selection, nailed it: in the tropics, “evolution has had a fair chance,” while glaciated zones faced “countless difficulties.”

Species That Can’t Hack Temperature Swings? They’re Already Extinct

No species survives without coping with fluctuations. Day-to-night shifts, seasonal changes—even tropics see rainy-dry season swings. Life adapts: hibernation, estivation, migration; panting to cool off or thicker fur to conserve heat. Honeybees contract thorax muscles for warmth; wood storks defecate on their legs to chill.

Over a species’ million-year lifespan, bigger climate shifts kick in. Earth has cooled for 40 million years, possibly from Himalayan uplift exposing rock to chemical weathering, sucking CO2 from the air. In the late Eocene, the planet was ice-free and sweltering. By 35 million years ago, Antarctica glaciated. Three million years back, the Arctic followed. Then, 2.5 million years ago, the Pleistocene began: recurring ice ages driven by orbital wobbles from Jupiter and Saturn’s gravity.

These tweaks redistribute summer sunlight to northern latitudes. Less light means snow buildup, triggering a feedback loop—CO2 drops, temps plunge, ice grows. Eventually, orbits shift, ice melts, CO2 rises, and thaw accelerates. Pleistocene saw this ~20 times; sea levels crashed 100 meters, crustal plates buckled under ice weight.

We’re All Cold-Adapted—And That’s the Key to Warming’s Impact

Every species alive today is cold-adapted. Golden tanagers, cock-of-the-rocks, blue jays, cardinals, barn swallows—they endured the last ice age, and their kin survived the 20 before, back 2.5 million years. Glacials dominated (lasting longer than interglacials), so evolution favored winter hardiness. For 2.5 million years, no premium on heat tolerance—temps never spiked much beyond today’s.

We’re at an interglacial peak now. Polar icons grab headlines, but tropical and temperate survivors have ice age pedigrees. Global warming tests heat coping, but history suggests most will manage—unlike those brittle ice-dependent holdouts.

Source : The Sixth Extinction: An Unnatural History by Elizabeth Kolbert

Goodreads : https://www.goodreads.com/book/show/17910054-the-sixth-extinction

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