If you hang out up high with rock climbers, or anything involving naked exposure to dizzying altitude, sooner rather than later most novices will experience complete, total paralyzing fear. Climbers call it being gripped. And soon after being gripped, maybe while sheepishly checking your clothes for stains on the ground, a kindly veteran climber may comfort you with "the apes that were afraid of heights learned how to walk." After a few climbs, fear turns into exhilaration. Pretty soon, you're up high looking down, and instead of nervous you feel safe up there, downright privileged in fact. Like "neener neener neener, you can't get me!" I often wondered if that wasn't an even more ancient evolutionary hangover, an echo from an earlier life, before we learned to walk, a life high in the canopy. Thanks to present day habits, our descendents may quickly discover, or rediscover, if that's the case. Let's explore below the fold.
The Miocene was cool time for a warm epoch. Cool in the sense that it was really neat. Much of Eurasia and Africa was covered in vast, steamy rain forests, the archtypical jungle. It was warm in the beginning even near the poles, there were no big, permanent ice-caps like we see today. The Miocene lasted for almost 20 million years, right up until a few million years ago, and it was a prosperous time. Sea levels were higher, early whales reached their greatest diversity, same for many land-based orders and genera, all across a land teeming with life and rarely troubled by glaciers.
Our own ancestors were no exception, they boomed with the land. Sadly, dense jungle isn't the greatest enviroment for fossilization. The soil is acidic, insect armies patrol the dimly lit floor, and if something falls from the trees it doesn't last long. But we've found a few hardy remnants. They speak of a rich tapestry of primates including the first apes, from the tiny to the largest known. Based on a handful of diverse teeth, a few jawbones, and scattered bits of skull, it is inferred there were so many living in the Miocene that the period is sometimes nick-named the age of the apes.
On the large side was Gigantopithicus, where one variety is estimated to have reached ten feet tall! It's debatable if such a creature actually spent any time in the canopy. But the ancient forest was robust, full of mature trees. Still, some modern day apes are sizable and still move through the highest tree tops with astonishing ease. Either way, the trees would probably have worked well for younger gigantos. The smallest apes we know of were about the size of a house cat. Micropithecus has been compared to a miniature gibbon. If they were anything like a modern day gibbon, these little guys probably raced through the trees in a blur.
In between those two extremes were all kinds of apes we know very little about. Sivapithecus, Dryopithecus, Heliopithecus, Oreopithecus, and more, something like 30 to 100 species depending if the anthropologist you're asking is a lumper or a splitter. The debate rages over which Miocene ape might have been ancestral to what modern clade, especially humans, but without better fossils—and lots of them—that debate will probably never be settled.
The days of the Miocene were numbered, just like any other time. It was doomed by the fate of Antarctica. At the start of the Miocene, Antarctica was probably unrecognizable compared to today, lush and green and full of life. But early in the Miocene, the land bridge connecting South America and Antarctica finally disappeared. Over the next ten million years Antarctica was thermally isolated by the rise of the great southern circumpolar current that still rings the icy land today. Rain or snow falling in the newly exiled continent was stuck as ice. The ice built up and up and up ... Until it was thousands of feet thick, until it flowed under its own weight over the frozen ground like cold molasses. One giant glacier flowed east, the other west, split by the buried continental divide, grinding up the rock and soil on the surface, eventually dropping the deposits into the southern ocean along with who knows what priceless fossil treasures. The earth dried out and cooled. That was the end of the Miocene. Which was good, for us.
As idyllic as a jungle paradise might sound, it's not our world. As the ice caps formed, Earth slipped into a metastability governed by orbital mechanics and a subtle interplay of atmospheric gasses. The great forests faded away, great plains formed instead, wooded river bottoms surrounded by savanna popped up, some of the old rain forests and plains eventually turned into the largest deserts on earth. Some apes continued to get by staying in trees and do to this day—as long as the trees remain. Gibbons and orangutans flourished in hunks of left-over rainforest. Others, much like chimps and gorillas, probably became increasingly terrestrial, able to get by on the ground for long periods of time, but still able to retreat into the canopy for safety. Our ancestors include the few species of late Miocene ape that learned to scamper about like that. One of them developed the abilty to walk quite well, for long distances, and that one eventually gave rise over several million years to a whole new clade of bipedal ape well adapted for grasslands. Of those apes that habitually walked on two legs and highly specialized feet in the African savana for millions of years, we are the sole extant survivor.
Technically, the earth might still be called a planet of the apes since we're so numerous and successful for now. Humans are so geographically dispersed and so clever it is likely at least some of us could survive a truly terrible event. Enough could live through a K-T level impact or a full nuclear strike, in hidden shelters with stored provision or out of sheer luck, that we would probably be preserved as a species for at least a few generations. But what then? How much can we weather and for how long? What is the long-term survival going to be like for our distant descendants?
That's a good question in light of recent climate data. We don't know how far climate change will go. But the benchmark of 400 ppm of CO2 has been reached, and 400 ppm rivals Miocene conditions. And while geologic epochs may seem to move quickly when examining the fossil record, we are changing the climate orders of magnitude faster than anything we know of in the past, outside of a big meteor, and there is no end to our fossil fuel emissions in sight. We're going to heat things up, a lot. It's already baked in. If we don't stop soon we could add perhaps a full 10 degrees or more to the global temperatre average within a century or two. Enough to melt every significant patch of ice and threaten every biome on the planet.
Prior periods in which the temperature jumped dramatically, globally, and quickly include the Paleocene-Eocene Thermal Maximum about 55 million years ago and the Permian-Triassic Extinction about 250 mya. By quickly, paleobiolgoists and paleoclimatalogists mean the change happened over a minimum of 20,000 years, if not longer. In the most rapid scenario during the PETM the temperature changed by about 0.0003 °C (.00055 °F)/year. It's doubtful you'd even notice that over the course of a human lifetime unless you happened to be the lucky ducky around for a big tipping point. We have the potential to change global climate a thousand times faster, ten degrees or more in a few hundred years. A blink in geologic time. That's unprecedented, utterly unpredictable, and that's why it's the most important long term issue we face as a nation and a planet.
Maybe we'll initially survive that climate catastrophe only to go extinct in the new growing deserts. Or barely cling on here and there in some patches of struggling forests and grasslands. The climate will be chaotic for a long time, millennia. But it will eventually stabilize in some fashion. When that happens it seems possible the great Miocene jungles may bloom again. And if our DNA is still alive and kicking, we could be right back where we started, only the apes that aren't afraid of heights will be the ones better suited to survive. Or maybe, just maybe, we can get on top of this and spare ourselves a lot of bother.