We Don’t Have Infinite Time

by Sean Kane

Although recreational running can feel like a chore, our species is built for insane endurance. Plenty of land animals are faster in short distances, but nothing can move at a slow, easy run for longer than humans.

This allowed prehistoric humans to excel at hunting. We’d jog after large prey under the midday sun until they died from exhaustion.

Once our weapons got better and we learned to carry water in containers, our already impressive endurance only improved, readying humans to spread across the globe.

Our ability to regulate body temperature further helped our crazy endurance abilities. Humans can really take the heat.

Many animals sweat, but few use it for evaporative cooling, like humans (and horses) do. We’re also able to breath through our mouths when we run, taking in more oxygen as well as further dissipating heat.

Other animals dump heat by panting, which is impossible to do in a gallop. This meant hunters could chase animals at their slowest galloping speed until they overheated

Another huge evolutionary advantage came from our ability to stand upright — though creaky knees and back pain are certainly a tradeoff.

Standing on two legs kept more of our hairless skin out of the harsh savanna sun and, even more importantly, freed up our hands to wield tools and to throw weapons.

Though other primates have the ability to understand the trajectories of thrown objects (allowing them to dodge), no animals can aim and throw with the power and precision of a human.

We’ve also got better hearing than our other primate brethren, and we can hear a wider range of sounds, especially between 1.0-6.0 kHz — where most human speech occurs.

Around 70,000 years ago, humanity’s global population dropped down to only a few thousand individuals, and it had major effects on our species.

It’s called the Toba catastrophe. A massive supervolcano in Indonesia erupted, blackening the sky with ash, plunging earth into an ice age, and killing off all but the hardiest humans.

The enormous supervolcano eruption occurred around the same time as humanity’s biggest bottleneck. Research from the late 1990s and early 2000s suggested that this eruption, on Sumatra in Indonesia, blocked the sun across much of Asia, causing a harsh volcanic winter and a 1,000-year-long cooling period on earth.

But archaeological evidence shows that human hunter-gatherer settlements in India weren’t too affected by the eruption and quickly recovered. Temperature data embedded in the geology of Lake Malawi, in East Africa, also suggests that the region didn’t cool off that drastically.

But worldwide the population declined rapidly.

Almost getting wiped out put a lot more pressure on our ancestors and caused a genetic bottleneck, which greatly decreases the genetic variation in a population.
Small populations are much more susceptible to disease and environmental disasters, and unfavorable genetic traits can rapidly accumulate. Bottlenecks also slow evolutionary change, since fewer members of a species are around to pick up potentially favorable genetic mutations.

However, any rare beneficial mutations that do occur get amplified: Genes get passed around quickly in a tiny community.

Genetic bottlenecks can cause what is known as the founder effect, where small, isolated populations drastically diverge from the original population.

As humans spread across the planet, our population experienced multiple bottlenecks and, as a result, a serial-founder effect kicked in to create the diversity we currently see in the human race today.

Scientists have mapped these events to geographic choke points around the world, based on decreasing genetic diversity as we migrated.

One bottleneck occurred when a small group of humans left Africa.

Another happened when this group split up in the Middle East, with some of us heading to Europe and others to Asia.

Others occurred when we left Southeast Asia for Austronesia, crossed the Beringia land bridge into Alaska, and spread into South America through what is now Panama.

This is why African populations tend to have far more genetic diversity in their DNA than populations native to the Americas.

It’s also why, when you compare humans to other species, human DNA is not very diverse when you consider our globe-spanning range.

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