Modern Humans Evolved During Glacial & Interglacial Periods - Earth Had Ice For Only 13% Of Past 485 Million Years

[hatrack]

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Using fossil evidence to help reconstruct the past 485 million years, scientists found that Earth contained ice only 13 percent of the time — including the ice age that humans are accustomed to today. The rest of the time, it was iceless and often with much higher temperatures than what is the norm today. Importantly, researchers found that high carbon dioxide levels were linked with periods known as “greenhouse” Earth — when conditions were iceless and much hotter. Levels fell during the colder periods and brought icy patches called an “icehouse” Earth.

“Carbon dioxide is kind of the main driver, because the relationship between our record of carbon dioxide and our record of Earth’s temperature is very close throughout the Phanerozoic,” said Jessica Tierney, a paleoclimatologist who helped parse out Earth’s temperature history. But what caused carbon dioxide to fall and make an iceman cometh? And, as we veer away from widespread ice, scientists weigh if humans have an evolutionary advantage to live through warmer temperatures than life before us.

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While an icy Earth is uncommon, it is all that modern humans have known. But these icehouse conditions may have provided a beneficial push for human evolution across our planet. The actual ice throughout human history wasn’t important for evolution, paleoanthropologist Rick Potts said. But the climate and weather variations on our planet — brought on by cold poles and a warm equator — drove us to become a highly adaptable species.

“We are part of an evolutionary tree with a lot of examples of extinction,” said Potts, head of the Smithsonian’s Human Origins Program. “We are the last two-legged creature standing out of our evolutionary tree. We’re very, very adaptable.” It’s natural selection in a nutshell, he said. But it serves as an important reminder that natural selection isn’t just an adaptation to a single type of environment but adjustments when that environment or other factors change.

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https://www.washingtonpost.com/climate-environment/2025/02/20/ice-caps-rare-earth-history-human-survival/

[eppur_se_muova]

1. Natural ice provides a way of preserving meat through the Winter -- a big boon to pre-mechanical populations.

Much of Earth's human population, for much of history, was never too far from at least seasonal ice. Those who lived closer to the equator had to rely on fresh fish and game year-round. Not possible everywhere, which somewhat limited human expansion.

[hatrack]

2. Also, the colder, the bigger . . .

In the context of the biological rule that the closer you get to the poles, the bigger the animal, which is handy if you're hunting - in today's terms, deer and black bear (temperate) vs. caribou and polar bear (arctic).

More meat per successful hunt (plus ice for storage!) improves the tribe's odds of survival.